Indications, complications, and mortality rate following craniotomy or craniectomy in dogs and cats: 165 cases (1995–2016)

Bridget A. Morton Department of Veterinary Clinical Medicine, College of Veterinary Medicine, University of Illinois, Urbana, IL

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Laura E. Selmic Department of Veterinary Clinical Sciences, College of Veterinary Medicine, The Ohio State University, Columbus, OH

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Samantha Vitale Department of Veterinary Clinical Medicine, College of Veterinary Medicine, University of Illinois, Urbana, IL

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Rebecca Packer Department of Clinical Sciences, College of Veterinary Medicine & Biomedical Sciences, Colorado State University, Fort Collins, CO

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Lawrence Santistevan Department of Clinical Sciences, College of Veterinary Medicine & Biomedical Sciences, Colorado State University, Fort Collins, CO

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Beth Boudrieau Department of Small Animal Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, TX

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Whitney Hinson Department of Small Animal Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, TX

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Marc Kent Department of Small Animal Medicine and Surgery, College of Veterinary Medicine, University of Georgia, Athens, GA

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Devon W. Hague Department of Veterinary Clinical Medicine, College of Veterinary Medicine, University of Illinois, Urbana, IL

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Abstract

OBJECTIVE

To determine the most common indications for cranial surgery and identify risk factors associated with the occurrence of complications and death in the perioperative period following cranial surgery.

ANIMALS

150 dogs and 15 cats.

PROCEDURES

For this multi-institutional retrospective case series, medical records of dogs and cats that underwent cranial surgery at any of the 4 participating institutions between 1995 and 2016 were reviewed. Variables were evaluated included species, sex, age, neurolocalization, history of preoperative seizures, surgical approach, histological results, perioperative complications, and outcome. Logistic regression analysis was performed to assess for risk factors for complications.

RESULTS

The most common neurolocalization was the forebrain (110/165 [66.7%]), with 94 (57.0%) animals having had seizures preoperatively. The rostrotentorial (116/165 [70.3%]) and caudotentorial (32/165 [19.4%]) surgical approaches were most commonly reported. The most common indication was the treatment of meningioma (75/142 [52.8%]). Complications arose in 58 of the 165 (35.2%) cases within 24 hours and in 86 (52.1%) cases 1 to 10 days postoperatively. Perioperative complications included hypotension (38/165 [23.0%]) and anemia (27/165 [16.4%]). During the postoperative period, the most common complications were neurologic deficits, seizures, postoperative anemia, and aspiration pneumonia. The mortality rate with death or euthanasia perioperatively or ≤ 10 days postoperatively was 14.5% (24/165). Long-term complications occurred in 65 of the 165 (39.4%) animals, with seizures and neurologic deficits being the most common.

CLINICAL RELEVANCE

Cranial surgery was performed most commonly for the removal of neoplastic lesions in dogs and cats, and most complications were not life-threatening.

Abstract

OBJECTIVE

To determine the most common indications for cranial surgery and identify risk factors associated with the occurrence of complications and death in the perioperative period following cranial surgery.

ANIMALS

150 dogs and 15 cats.

PROCEDURES

For this multi-institutional retrospective case series, medical records of dogs and cats that underwent cranial surgery at any of the 4 participating institutions between 1995 and 2016 were reviewed. Variables were evaluated included species, sex, age, neurolocalization, history of preoperative seizures, surgical approach, histological results, perioperative complications, and outcome. Logistic regression analysis was performed to assess for risk factors for complications.

RESULTS

The most common neurolocalization was the forebrain (110/165 [66.7%]), with 94 (57.0%) animals having had seizures preoperatively. The rostrotentorial (116/165 [70.3%]) and caudotentorial (32/165 [19.4%]) surgical approaches were most commonly reported. The most common indication was the treatment of meningioma (75/142 [52.8%]). Complications arose in 58 of the 165 (35.2%) cases within 24 hours and in 86 (52.1%) cases 1 to 10 days postoperatively. Perioperative complications included hypotension (38/165 [23.0%]) and anemia (27/165 [16.4%]). During the postoperative period, the most common complications were neurologic deficits, seizures, postoperative anemia, and aspiration pneumonia. The mortality rate with death or euthanasia perioperatively or ≤ 10 days postoperatively was 14.5% (24/165). Long-term complications occurred in 65 of the 165 (39.4%) animals, with seizures and neurologic deficits being the most common.

CLINICAL RELEVANCE

Cranial surgery was performed most commonly for the removal of neoplastic lesions in dogs and cats, and most complications were not life-threatening.

Introduction

In dogs and cats, cranial surgery has become more common due to advances in diagnostic imaging and a better understanding of pathophysiology and prognosis. Cranial surgery may be performed for a number of different reasons including traumatic brain injury, neoplasia, malformations, and various intracranial cysts and diverticula.16

Morbidity and death following cranial surgery may be associated with the underlying disease, damage to nervous tissue, or both. Reported complications with cranial surgery include aspiration pneumonia, increased intracranial pressure secondary to the disease or as a consequence of iatrogenic injury or tissue trauma, anemia due to blood loss, and seizures.610 Advances in surgical technique, anesthetic drugs, and systemic monitoring have improved the outcome of the surgical procedure.5,11,12 Publications that evaluate the type and rate of complications and perioperative death associated with cranial surgery including perioperative death and identify risk factors for these problems following cranial surgery are limited. This information has practical value to inform clinical practice and facilitate educated decision-making and informed consent for our clients.

The primary objectives of the study reported here were to determine the most common indications for cranial surgery, investigate perioperative complications and death following cranial surgery, and identify risk factors associated with the occurrence of complications and death following cranial surgery. We hypothesized that animals that underwent surgical approaches located rostral to the tentorium would have lower odds of perioperative complications, compared to those that had approaches located caudal to tentorium. We postulated this rostrotentorial approach may be associated with reduced complications such as hemorrhage and cerebral swelling due to the fact that important vasculature, such as the dorsal sagittal sinus, could be more easily avoided.

Materials and Methods

Case selection criteria

The medical record databases from the veterinary medical teaching hospitals of the University of Illinois at Urbana-Champaign, University of Georgia, Colorado State University, and Texas A&M University were searched for records of dogs and cats that underwent craniotomy or craniectomy between January 1, 1995, and June 1, 2016. Cases were included if they had preoperative cross-sectional imaging with a complete medical record including the surgical approach. Cases were excluded if they did not have a complete medical record. Due to this being a retrospective study, ethical consent for animal use was not requested.

Medical records review

For each dog or cat enrolled in the study, data extracted from the medical record included signalment, body weight, presenting complaint, whether the patient had a history of seizures, results of physical and neurologic examinations, CBC abnormalities, serum biochemical analyses abnormalities, and clinical staging results from thoracic and abdominal imaging. Results of CT and MRI were reviewed, including size and description of the lesion. Surgical approach, histological diagnosis of excised tissue, and whether adjunctive chemotherapy or radiation therapy was added were reviewed. Surgical approaches were determined based on previous descriptions,5,9,13 with approaches being categorized as rostrotentorial, caudal tentorial, or other. Rostrotentorial approaches were considered any surgical approach or combination of approaches that were located rostral to the tentorium, and caudal tentorial approaches were any surgical approach or combination of approaches that were located caudal to the tentorium. Transtentorial approaches and minimally invasive surgical approaches were categorized as other. Perioperative data collected included the size of the craniotomy or craniectomy defect as stated in the surgical report; whether or not cranial reconstruction was performed; the method of reconstruction; whether anticonvulsants were used; whether corticosteroids were used; anesthetics and drugs used before, during, or after surgery; duration of anesthesia and surgery; and the presence of epistaxis, hypotension (mean arterial pressure [MAP] < 70 mm Hg), cardiac arrhythmias, hemorrhage, or aspiration pneumonia.

Postoperative data were collected, which included whether the patient was fed within the first 24 hours, whether or not the patient received fentanyl (or other opioid), and whether the patient received medications for prevention or treatment of gastrointestinal ulceration. The timing of feeding was included to determine how many patients were able to eat within 24 hours and whether this contributed to the risk of complications, in particular aspiration pneumonia. A previous report9 stated that aspiration pneumonia after intracranial surgery typically occurs around 4 days from the time of the anesthetic event. The time period of 24 hours was chosen in this study to determine whether there was any association between feeding immediately versus waiting to feed and risk of complications. Data were collected regarding the occurrence of complications in the perioperative period within 3 different time periods: during surgery and within 24 hours of surgery, between 1 to 10 days following surgery, and > 10 days after surgery. Data were assessed regarding the occurrence of hypotension (MAP < 70 mm Hg), anemia (PCV < 25%), epistaxis, hyperthermia (rectal temperature > 39.7 °C), seizures, neurologic deficits, suspected high intracranial pressure (defined as changes consistent with a Cushing reflex with hypertension [MAP > 90 mm Hg] and bradycardia [HR < 60 beats/min)]), respiratory compromise (defined by hypoventilation and hypoxemia through any cause including aspiration pneumonia), aspiration pneumonia (based off radiographs), bradycardia (< 60 bpm in dogs and < 140 bpm in cats), and surgical site infection confirmed by culture. For each patient, survival up to 10 days as well as > 10 days following surgery was documented. In addition, the reason for death or euthanasia was ascertained. Seizures and neurologic deficits were counted as a complication depending on whether they were present preoperatively or were a new problem given the limitations of retrospective medical record assessment for determining improvement or worsening of specific neurologic deficits.

Statistical analysis

Continuous data were assessed for normality using histograms, skewness, kurtosis, and Shapiro-Wilk tests. These data were described using the mean and SD if normally distributed or median and the range if nonnormally distributed. Frequencies and percentages were used to describe categorical data.

Univariable logistic regression analysis was used to test for associations between variables of interest and complications occurring < 24 hours postoperatively, 1 to 10 days postoperatively, > 10 days postoperatively, or death within 10 days postoperatively to select variables for the multivariable modeling. Variables assessed for associations with complications included species, brachycephalic breed, age, body weight, whether animals had a history of seizures, whether animals had preoperative decreased mentation, preoperative neurolocalization, surgical approach, size of mass if present, duration of anesthesia, if cancer was identified on histopathology, if fentanyl or an opioid was administered in the perioperative period, and whether feeding occurred within 24 hours after surgery. Additional variables assessed for associations with complications occurring within 1 to 10 days postoperatively included whether anticonvulsants were administered postoperatively. Variables assessed for complications occurring at > 10 days postoperatively included whether the animal developed postoperative respiratory compromise. Variables assessed for associations with death occurring within 10 days postoperatively included species, brachycephalic breed, age, body weight, whether the animal had a history of seizures or decreased mentation preoperatively, surgical approach, neurolocalization, size of mass if present, whether cancer was present on histopathology, whether total IV anesthesia with propofol versus inhalation anesthesia was used, duration of anesthesia, presence of intraoperative arrhythmias, whether fentanyl or an opioid was administered perioperatively, the use of an anticonvulsant medication or gastroprotectant postoperatively, postoperative aspiration pneumonia, postoperative respiratory compromise, whether mannitol was administered postoperatively, and whether feeding occurred within 24 hours after surgery.

Multivariable logistic regression modeling was performed for each outcome variable (complications within the first 24 hours, 1 to 10 days, or > 10 days after surgery and death within 10 days after surgery) by use of backward selection, including all variables in the first model that had α < 0.2 in the respective univariable results. Variables were retained in the model if α < 0.05. The statistical analysis was performed with commercially available software packages (SAS version 9.3; SAS Institute Inc; Prism version 6; GraphPad Software), and statistical significance was set at values of P < 0.05.

Results

There were 165 animals (150 [90.9%] dogs and 15 [9.1%] cats) that met the inclusion criteria. Of the 165 animals, 81 (49.1%) were female (78 [47.3%] spayed and 3 [1.8%] sexually intact), and 84 (50.9%) were male (77 [46.7%] castrated and 7 (4.2%) sexually intact). The median age was 9.0 years (range, 0.2 to 15 years). Median body weight was 24.1 kg (range, 1.5 to 58.0 kg). Thirty-seven (22.4%) dogs were of mixed breed, and the most common canine purebreds represented were Labrador Retriever (15 [9.1%]), followed by Golden Retriever (10 [6.1%]), Boston Terrier (9 [5.5%]), Boxer (7 [4.2%]), and German Shepherd Dog (7 [4.2%]). There were 5 (3%) Cavalier King Charles Spaniels, 4 (2.4%) Bichon Frise, 4 (2.4%) French Bulldogs, 3 (1.8%) Australian Shepherds, 3 (1.8%) Chihuahuas, 3 (1.8%) Doberman Pinschers, and 3 (1.8%) Staffordshire Terriers. There were 2 (1.2%) dogs of each of the following breeds: American Pit Bull Terrier, English Setter, English Springer Spaniel, Maltese, Miniature Schnauzer, Shetland Sheepdog, and Weimaraner. There was 1 (0.6%) dog of each of the following breeds: Airedale, Akita, Australian Cattle Dog, Beagle, Border Collie, Cocker Spaniel-Poodle cross, Cocker Spaniel, English Bulldog, Flat-Coated Retriever, German Shorthaired Pointer, Great Dane, Greyhound, Irish Wolfhound, Italian Greyhound, Jack Russell Terrier, Keeshond, Leonberger, Old English Sheepdog, Pomeranian, Samoyed, Schipperke, Shiba Inu, Standard Poodle, Toy Poodle, Vizsla, and Yorkshire Terrier. The 15 cats were reported as domestic longhair (4 [2.4%]), domestic shorthair (5 [3.0%]), calico (1 [0.6%]), Maine Coon (2 [1.2%]), Persian (1 [0.6%]), Ragdoll (1 [0.6%]), and Siamese (1 [0.6%]). Twenty-seven animals were of brachycephalic breeds.

Ninety-four (57.0%) patients had a history of seizures at the time of initial evaluation. Mentation at presentation was primarily noted as bright, alert, and responsive (92 [55.8%]), followed by dull and obtunded (34 [20.6%]); quiet, alert, and responsive (33 [20.0%]); and fractious (6 [3.6%]). Neurologic deficits upon initial evaluation included postural reaction deficits (81 [49.1%]), cranial nerve deficits (61 [37.0%]), ataxia (56 [33.9%]), and vestibular signs such as head tilt and nystagmus or strabismus (42 [25.5%]). Of the total patients with neurologic deficits, 27 (17%) of them had seizures. Neurolocalization was reported as follows: forebrain (110 [66.7%]), not specified (13 [7.9%]), brainstem and central vestibular (20 [12.1%]), cerebellum (9 [5.4%]), normal (5 [3.0%]), and multifocal (6 [4.8%]). The median duration of clinical signs prior to presentation was 4.0 days (range, 0 to 432 days).

The serum biochemistry abnormalities most commonly reported were high alkaline phosphatase activity (64/165 [38.8%]), followed by high alanine aminotransferase activity (47/165 [28.5%]) and hypernatremia (30/165 [18.2%]). Results of CBCs showed neutrophilia 49 of the 165 (29.7%) animals, thrombocytopenia in 17 (10.3%), and thrombocytosis in 6 (3.6%). Reports for thoracic radiography were available for review in 116 of the 165 (70.3%) cases; abnormalities were reported in 21 of these 116 (18.1%) of cases. These abnormalities included bronchial lung pattern (2/165 [1.2%]), alveolar pattern (2/165 [1.2%]), bronchointerstitial pattern (10/165 [ 6.1%]), cardiomegaly (6/165 [3.6%]), or soft tissue pulmonary nodules (1/165 [0.6%]), alone or in combination. Abdominal ultrasonography was performed in 79 of the 165 (47.9%) cases. Abnormalities that were reported included hepatomegaly (12/79 [15.1%]), splenic nodules (9/79 [11.4%]), splenomegaly (9/79 [11.4%]), bilateral adrenomegaly (6/79 [7.5%]), or a liver mass (6, [7.5%]), alone or in combination.

Most animals (145/165 [87.9%]) had a brain MRI performed for diagnostic and surgical planning purposes. Skull CT was performed in 36 of the 165 (21.8%) cases. Cerebrospinal fluid analysis was performed in 22 of the 165 (13.3%) cases, with 11 of these 22 (50.0%) cases having had abnormalities detected and 6 (27.2%) having had clinically normal results documented for CSF analysis. The remaining cases were documented to have CSF sampled, but the reports were not available for review. The most common CSF abnormality was high protein concentration.

Preoperative treatments were performed on some patients. Two of the 165 (1.2%) animals underwent radiation therapy historically for disease processes (1 for nasal sarcoma and 1 granulomatous meningoencephalitis) that occurred prior to the onset of neurologic signs. No animals were treated with chemotherapeutics prior to surgery. Eighty-four (50.9%) patients were receiving prednisone treatment prior to surgery. Eighty-one of the 165 (49.1%) patients were receiving anticonvulsant treatment prior to surgery, with single-agent phenobarbital being the commonly reported agent used (55/165 [33.3%]). Single-agent levetiracetam was the second most commonly reported anticonvulsant agent used (15/165 [9.1%]). Other agents or combinations of anticonvulsant agents that were reported included a combination of phenobarbital and potassium bromide (3/165 [1.8%]), pregabalin (2/165 [1.2%]), diazepam (1/165 [0.6%]), gabapentin (1/165 [0.6%]), a combination of levetiracetam and potassium bromide (1/165 [0.6%]), a combination of phenobarbital and levetiracetam (1/165 [0.6%]), or zonisamide (1/165 [0.6%]). Nineteen of the 165 (11.5%) animals were receiving antimicrobials prior to surgery, 20 (12.1%) were receiving medications for treatment or prevention of gastric ulceration, and 1 (0.6%) was receiving antifungal treatment.

The most common indications for cranial surgery in this study was for open biopsy or resection of a mass lesion (126/165 [76.4%]; Table 1). Eight (0.05%) of the animals only had an open biopsy performed. Therefore, most animals did not have a biopsy before definitive surgery and received surgery for resection of a mass lesion for diagnostic and therapeutic purposes. Other reasons (eg, trauma or minimally invasive biopsy [scope assisted]) were grouped together (29/165 [17.6%]). The most common surgical approach was a rostrotentorial craniotomy or craniectomy, which was performed for 116 of the 165 (70.3%) animals, followed by caudal tentorial approaches performed for 32 (19.4%) animals. Other approaches were performed for 17 (10.3%) animals.

Table 1

Indications for cranial surgery in 165 animals (150 dogs and 15 cats) that underwent craniotomy or craniectomy between January 1, 1995, and June 1, 2016, at any of 4 participating veterinary teaching hospitals and for which the medical records were complete, including preoperative cross-sectional imaging and surgical approach.

Indication for surgery No. (%) of animals
Primary tumor 126 (76.4)
Secondary or metastatic tumor 9 (5.4)
Primary and secondary tumor 1 (0.6)
Other
 Chiari malformation 3 (1.8)
 Pyogranulomatous inflammation 1 (1.0)
 Unknown due to inconclusive histopathology 19 (11.5)
 Encephalitis 2 (1.2)
 Abscess 1 (1.0)
 Trauma 3 (1.8)

A dural substitute (DuraGen Secure Dural Regeneration Matrix; Integra LifeSciences Corp) was used to aid in dural closure in 38 of the 165 (23.0%) cases. An absorbable gelatin sponge was used in 18 of the 165 (10.9%) cases. Porcine small intestinal submucosa was used in 31 of the 165 (18.8%) cases. The median longest length of size of mass was 2.2 cm (range, 0.3 to 10.0 cm). The median longest length of the craniotomy or craniectomy defect was 2.0 cm (range, 0.3 to 20.0 cm).

Histopathology was performed in 142 of the 165 (86.0%) cases; the most common histopathologic diagnosis was meningioma (75/142 [52.8%]), followed by glioma (19/142 [13.3%]; 9 with astrocytoma, 7 with oligodendroglioma, and 3 with glioma) and then nonneoplastic etiologies (18/142 [12.6%]; 6 with encephalitis or meningitis, 3 with normal brain tissue, 2 with gliosis, 2 with hemorrhage, 1 each with abscess formation, fungal granuloma, parasitic granuloma, vascular injury, or inconclusive etiology). Of these 142 animals, primary bone tumors were diagnosed in 12 (8.6%; 10 with multilobular osteochondrosarcoma, 1 with multilobulated chondroma, and 1 with osteoma). Nonglial primary neurologic tumors (medulloblastoma, choroid plexus tumor, or granular cell tumor) affected 7 of the 142 (4.9%) animals, and secondary or metastatic tumor (differentiated sarcoma, nasal adenocarcinoma, and squamous cell carcinoma) affected 7 (4.9%). Round cell tumors affected 4 of 142 (2.8%) animals: 3 with histiocytic sarcoma and 1 with lymphoma. Twenty-three of the 165 (13.9%) animals did not undergo a histopathologic examination. The most commonly reported meningioma histopathologic subtypes were meningothelial (4/75 [5.3%]), angiomatous (2/75 [2.7%]), fibroblastic (3 [4.0%]), and transitional (2 [2.7%). The histopathologic subtype was not given for 24 (32.0%) of the reported animals affected with meningioma.

Perioperative antimicrobials were defined as before (at induction), during, and up to 24 hours after surgery. Most patients received cefazolin (147/165 [89.6%]) as a perioperative antimicrobial. The other antimicrobials administered included ampicillin (2/165 [1.2%]) and ampicillin and sulbactam (3/165 [1.8%]). An anticholinergic was administered as a premedication in 46 of the 165 (27.9%) patients. Most patients (150/165 [90.9%]) were premedicated with an opioid. Ninety of the 165 (54.6%) patients were premedicated with midazolam, and 21 (12.7%) received diazepam.

Intraoperative anesthetics were reported, and of the 165 patients, most were induced with propofol (134 [81.2%]), followed by thiopental (11 [6.7%]), midazolam (9 [5.5%]), not reported (7 [4.2%]), etomidate (2 [1.2%]), alfaxalone (1 [0.6%]), or diazepam (1 [0.6%]). Anesthesia was maintained with propofol continuous rate infusions for 69 of the 165 (41.8%) patients, isoflurane for 47 (28.5%), sevoflurane for 35 (21.2%) cases, not reported for 11 (6.7% cases), or 1 (0.6%) each with alfaxalone, desflurane, or midazolam. The median duration of anesthesia was 4.0 hours (range, 1.1 to 9.1 hours).

Fifty-three of the 165 (32.1%) patients were fed and ate < 24 hours following surgery, and 36 (21.8%) were first fed and ate ≥ 24 hours following surgery. The timing of feeding for the remaining 76 (46.1%) animals was not accurately reported. Within the postoperative period, 101 of the 165 (61.2%) patients received an anticonvulsant, 58 (35.2%) received a medication for prevention or treatment of gastrointestinal ulceration, 11 (6.7%) received mannitol, 82 (49.7%) received postoperative antimicrobials, and 113 (68.5%) received an opioid, with postoperative fentanyl administered to 58 of the 165 (35.2%) patients.

Complications

Complications occurring during surgery or within 24 hours after surgery—Complications occurred in this time period in 58 of 165 (35.2%) cases, with intraoperative hypotension reported in 38 (23.0%) and intraoperative arrhythmias reported in 33 cases (20.0%). Seizures occurred in 1 (0.6%) case within 24 hours of surgery. One (0.6%) patient was reported to have epistaxis, and anemia was reported in 27 (16.4%) cases. Sixteen (9.7%) patients received a perioperative blood transfusion. Aspiration pneumonia was diagnosed based on thoracic radiography in 6 (3.7%) within 24 hours of surgery. Four (2.4%) deaths were reported within the perioperative period. Details regarding decision-making were limited in the data provided; however, these cases were all reported to be euthanized on the table due to hemorrhage (eg, rupture of the basilar artery).

Complications 1 to 10 days after surgery—Complications arose during this time period in 86 cases of the 165 (52.1%) cases. The most common complications in this period were neurologic deficits, such as postural reaction deficits, cranial nerve deficits, and abnormal spinal reflexes, which occurred in 39 (23.6%) patients. Seizures occurred in 20 (12.1%) cases in this period. Postoperative anemia was reported in 22 (13.3%) cases, and epistaxis occurred in 10 (6.1%) cases. Aspiration pneumonia based on thoracic radiographs was reported in 16 (9.7%) cases, and respiratory compromise occurred in 13 (7.9%) cases. Six (3.7%) patients were presumed to have had high intracranial pressure postoperatively due to signs consistent with Cushing reflex (high blood pressure and bradycardia). Direct intracranial pressure monitoring was not reported in any of the cases. Three (1.8%) patients were reported to have hypotension as a short-term complication. Bradycardia occurred in 8 (4.9%) cases. One (0.6%) case had an infection postoperatively. Hyperthermia was reported in 14 cases (8.5%). Death occurred in 20 (12.1%) patients within 10 days of surgery. The cause of death was not reported in most cases.

Complications > 10 days postoperatively—Sixty-five of the 165 (39.4%) animals had complications that arose > 10 days after surgery. Seizures and neurologic deficits were reported > 10 days postoperatively in 38 (23.0%) and 45 (27.3%) cases, respectively. Seizures were part of the preexisting clinical signs in all animals except 1. Hyperthermia occurred in 9 (5.5%) cases. Suspected high intracranial pressure was reported in 8 (4.9%) cases due to signs consistent with Cushing reflex. Aspiration pneumonia based on thoracic radiography was reported in 7 (4.2%) cases. Hypotension and anemia were documented in only 1 (0.6%) case each, and epistaxis was not documented as a long-term complication. Four of the 165 (2.4%) animals were reported to have had a surgical site infection postoperatively.

There were 141 animals alive > 10 days after surgery. Of the remaining 141 animals, those that were reported to have died or have been euthanized > 10 days after surgery included 6 (4.3%) between 10 and 30 days postoperatively, 5 (3.5%) between 30 and 60 days postoperatively, 16 (11.3%) between 60 and 180 days postoperatively, 9 (6.4%) between 366 and 730 days postoperatively, and 4 (2.8%) > 731 days postoperatively. Thirty patients were lost to follow-up during this time period (> 10 days after surgery).

Risk factors

Multiple risk factors were evaluated by use of univariable analysis for significant associations with complications that developed during surgery or within 24 hours postoperatively, 1 to 10 days postoperatively, or > 10 days postoperatively (Table 2). For complications arising > 10 days after surgery, administration of fentanyl in the perioperative period was associated with greater odds of complications (OR, 8.2; 95% CI, 3.5 to 19.5; P < 0.001), compared to animals that did not have fentanyl. Animals with (vs without) respiratory compromise had a significantly higher odds of death within 10 days after surgery (OR, 24.4; 95% CI, 6.5 to 92.0; P < 0.001; Table 3).

Table 2

Results of the univariable analysis for factors associated with complications following cranial surgery for the animals described in Table 1.

Complications 1 to 10 days postoperatively Complications during surgery or within 24 hours postoperatively Complications > 10 days postoperatively
Variable OR (95% CI) P value OR (95% CI) P value OR (95% CI) P value
Species
 Feline 34.1 (1.7–672.1) 0.02 1.8 (0.6–5.6) 0.29 0.5 (0.2–1.8) 0.32
 Canine Referent Referent Referent
Brachycephalic 0.8 (0.3–2.0) 0.6 0.3 (0.1–0.8) 0.01 1.0 (0.4–2.5) 0.92
Age 1.1 (1.0–1.2) 0.27 1.0 (0.9–1.1) 0.36 1.0 (0.9–1.1) 0.72
Body weight 1.0 (0.9–1.0) 0.11 1.0 (0.9–1.0) 0.21 1.0 (0.9–1.0) 0.39
Preoperative history of seizures 0.4 (0.2–0.9) 0.02 0.6 (0.3–1.2) 0.13 1.7 (0.8–3.5) 0.17
Preoperative decreased mentation 1.4 (0.6–3.2) 0.46 1.1 (0.5–2.3) 0.89 1.3 (0.5–3.1) 0.62
Preoperative neurolocalization 0.93 0.71 0.56
Approach
 Rostrotentorial 1.4 (0.6–3.3) 0.47 0.8 (0.3–1.7) 0.48 1.0 (0.3–3.4) 0.99
 Caudal tentorial Referent Referent Referent
 Other 5.0 (1.1–23.4) 0.04 0.8 (0.4–8.3) 0.44
Lesion size 1.1 (0.7–1.8) 0.66 1.0 (0.7–1.4) 0.90 0.8 (0.6–1.3) 0.41
Total IV anesthesia with propofol 2.3 (1.1–4.8) 0.03 0.5 (0.3–1.0) 0.06 1.9 (0.9–4.1) 0.09
Duration of anesthesia 0.9 (0.7–1.1) 0.39
Timing of feeding
 < 24 h Referent Referent Referent
 ≥ 24 h 1.0 (0.4–2.5) 0.96 4.1 (1.4–12.1) 0.01 1.6 (0.5–5.1) 0.41
Cancer diagnosis on histopathology 0.6 (0.2–1.5) 0.24 0.8 (0.3–2.0) 0.88 0.5 (0.1–2.1) 0.66
Postoperative fentanyl administered 3.7 (1.7–8.1) 0.001 1.5 (0.8–2.8) 0.24 8.2 (3.5–19.5) < 0.001
Postoperative opioid administered 1.3 (0.5–3.1) 0.61 0.7 (0.3–1.6) 0.42 2.5 (1.0–5.9) 0.04
Aspiration pneumonia within 10 d after surgery 1.0 (0.2–3.8) 0.95
Respiratory compromise within 10 d after surgery 3.1 (0.3–28.9) 0.32
Postoperative anticonvulsant administered 1.0 (0.5–2.1) 0.89 1.0 (0.4–2.2) 0.97

— = Not calculated.

Table 3

Results for the univariable analysis for factors associated with death within 10 days after cranial surgery for the animals described in Table 1.

Death within 10 days after surgery
Variable OR (95% CI) P value
Species
 Feline 0.5 (0.1–3.3) 0.49
 Canine Referent
Brachycephalic 0.9 (0.3–3.3) 0.92
Age 0.8 (0.7–0.9) 0.03
Body weight 1.0 (0.9–1.0) 0.69
Preoperative history of seizures 0.8 (0.3–2.1) 0.72
Preoperative decreased mentation 1.6 (0.5–4.7) 0.40
Preoperative neurolocalization 0.28
Approach
 Rostrotentorial 1.0 (0.3–3.4) 0.94
 Caudal tentorial Referent
 Other 2.1 (0.3–14.3) 0.44
Lesion size (cm) 0.6 (0.3–1.2) 0.16
Total IV anesthesia with propofol 1.2 (0.4–3.0) 0.77
Duration of anesthesia 0.9 (0.7–1.2) 0.69
Intraoperative arrhythmia 1.0 (0.3–3.1) 0.99
Postoperative fentanyl administered 0.9 (0.3–2.6) 0.9
Postoperative opioid administered 0.8 (0.3–2.6) 0.74
Postoperative gastroprotectant administered 2.1 (0.7–6.1) 0.16
Timing of feeding
 < 24 h Referent
 ≥ 24 h 2.3 (0.6–8.0) 0.18
Cancer diagnosis on histopathology 0.3 (0.1–0.8) 0.02
Aspiration pneumonia within 10 d of surgery 4.0 (1.1–14.3) 0.03
Respiratory compromise within 10 d of surgery 24.4 (6.5–92.0) < 0.001
Postoperative anticonvulsant administered 1.0 (0.3–3.2) 0.95
Mannitol administered 1.6 (0.3–8.4) 0.85

— = Not calculated.

Multivariable analysis results indicated several factors were associated with complications during surgery and within 24 hours. including preoperative history of seizures, surgical approach, and postoperative fentanyl administration (Table 4). Animals that had a history of seizures preoperatively had 80% lower odds of complications (OR, 0.2; 95% CI, 0.1 to 0.7; P = 0.01) than animals without this history, with adjustment for surgical approach and fentanyl administration. Animals that had a rostrotentorial approach (OR, 5.1; 95% CI, 1.3 to 19.9; P = 0.02) or other approach (OR, 15.9; 95% CI, 2.1 to 119.3; P = 0.007) had greater odds of developing complications, compared to animals that had a caudal tentorial approach, with adjustment for fentanyl administration and preoperative seizure history. Animals that received postoperative fentanyl were 3.6 times as likely to develop complications (OR, 3.5; 95% CI, 1.7 to 8.4; P = 0.007), compared to animals that did not, with adjustment for surgical approach and preoperative seizure history.

Table 4

Results of the multivariable analysis for factors associated with complications during surgery or within 24 hours after surgery and complications within 1 to 10 days following surgery for the animals described in Table 1.

Complications during surgery or within 24 hours after surgery Complications within 1 to 10 days after surgery
Variable Adjusted OR (95% CI) P value OR (95% CI) P value
Preoperative history of seizures 0.2 (0.1–0.7) 0.01
Approach
 Rostrotentorial 5.1 (1.3–19.9) 0.02
 Caudal tentorial Referent
 Other 15.9 (2.1–119.3) 0.007
Total IV anesthesia with propofol 0.3 (0.1–0.9) 0.04
Timing of feeding
 < 24 h Referent
 ≥ 24 h 4.5 (1.4–14.3) 0.01
Postoperative fentanyl administered 3.5 (1.5–8.4) 0.007

— = Not calculated.

The multivariable analysis revealed that administration of total IV anesthesia with propofol and timing of feeding were significantly associated with complications that occurred 1 to 10 days postoperatively. Animals that received total IV anesthesia with propofol had 70% lower odds of complications (OR, 0.3; 95% CI, 0.1 to 0.9; P = 0.04) compared to animals that had inhalational anesthesia, with adjustment for timing of feeding. Not feeding animals until ≥ 24 hours postoperatively resulted in 4.5 times greater odds for complications than animals feed < 24 hours (OR, 4.5; 95% CI, 1.4 to 14.3; P = 0.01), with adjustment for administration of total IV anesthesia with propofol. The clinical reasons for withholding enteral nutrition were not available in the data provided.

Discussion

In this study, cranial surgery was performed on dogs and cats most commonly for biopsy or resection of neoplasia, with moderate incidence of complications but with a low perioperative mortality rate. To the authors’ knowledge, this is the first report focused on reporting complications in a large cohort of dogs and cats receiving cranial surgery for different indications. In addition, potential risk factors were evaluated within the study population during surgery or within 24 hours, 1 to 10 days postoperatively, and > 10 days postoperatively. The highest complication rates occurred during and within 24 hours of surgery. Several risk factors were significantly associated with the development of complications at different time periods. This study identified greater odds of complications during surgery and within 24 hours after surgery, with rostrotentorial and other approaches, compared to the caudal tentorial approach; therefore, we rejected our initial hypothesis.

The dogs and cats included in this study had comparable signalments to those in previous studies10,11,1317 and were primarily middle-aged adult to geriatric-aged dogs and cats. In our literature review of cranial surgery in dogs and cats, the major difference noted between species was the survival time in favor of cats’ long-term postmeningioma removal.6,10,15,17,18 We included dogs and cats together in this study due to the lack of evidence of significant differences between the species with regard to cranial surgery. Therefore, regarding complications with cranial surgery, we evaluated the variable of species in our statistical analysis to control for differences between species and found no significant associations with complications or death.

The animals diagnosed with neoplasia in this study were all older than 4 years of age. A previous study6 reported the median age for dogs and cats with primary brain tumors as 9 years of age.1,3 Large-breed dogs have been reported to develop primary brain tumors more commonly than small-breed dogs. The canine population in this study was consistent with these reports, with large-breed dogs most commonly reported followed by brachycephalic breeds. In both cats and dogs, the most common tumor in patients undergoing surgery was meningioma, which was consistent with our study findings.1,2,6,10,13,15,17 There is likely a bias toward meningiomas being reported more commonly due to the potential for a better outcome with surgery compared to intra-axial tumors.1,15,16 The animals in our study younger than 4 years of age had head trauma, congenital malformation, or infectious or inflammatory processes.

We hypothesized that dogs and cats that underwent a rostrotentorial approach would have less complications during and following surgery; however, data from the present study did not support this hypothesis. Our initial hypothesis of a rostrotentorial approach being associated with fewer complications was based on the fact that important vasculature, such as the dorsal sagittal sinus, could be more easily avoided. This study identified greater odds of complications for dogs undergoing the rostrotentorial approach compared to caudal tentorial approaches. Possible reasons for this could have been that approaches that involve entering the nasal cavity, such as some rostrotentorial approaches, which may put the patient at added risk of different complications including pneumocephaly, and infection, especially if there is a need for reconstruction techniques requiring implants.19,20 We suspect that the patients that had rostrotentorial approaches also may have had a higher risk of seizures or a propensity for tumors in that region to be larger, potentially more invasive, and ill-defined.16,21,22 Our study did not find evidence to support the size of the lesion being a risk factor for complications because the size of mass was not adjusted to patient size and other factors may have confounded an association such as invasiveness of mass.

Previous studies6,21,23 have documented the complexity and risks associated with surgical approaches to the rostral portion of the brain. These typically include a rostrotentorial approach, transfrontal approach, or a combination of several techniques.13 Lesions that extend across the midline typically require bilateral approaches. In the present study, we did not specifically assess whether defects made were unilateral or bilateral. It follows that larger defects may require reconstruction using implants, which may predispose the patient to a greater risk of complications (eg, duration of surgery time, infection, and hemorrhage). However, this theory was not supported in our study, as the size of the defect was not associated with a greater risk of complications. We also did not correct or account for the size of the patient in relation to size of the defect in assessment of the data.

During surgery and within 24 hours postoperatively, animals that had postoperative fentanyl had greater odds of complications. During this time period, common complications included intraoperative hypotension and arrhythmias. It could be postulated that patients may have received fentanyl intraoperatively to decrease anesthetic medication requirements to reduce vasodilation caused by some anesthetic agents in response to intraoperative hypotension. In addition, opioid administration can lead to bradycardia, which may be more likely when administered at higher doses when patients are anesthetized. Postoperatively, a fentanyl constant rate infusion may have been used, which could have resulted in sedation, thus possibly increasing the risk of aspiration pneumonia, hypotension, or hypothermia.6,9 Another theory was that patients with more extensive or invasive procedures may be more likely to have been administered a fentanyl constant rate infusion instead of intermittent opioid injections. Therefore, these patients may be at greater risk of complications due to the invasiveness of the procedure and not necessarily from receiving fentanyl. Additional studies comparing postoperative analgesia protocols with intracranial surgery would be needed to determine an association between these factors. A major challenge with that type of study is the absence of a control group.

A history of seizures preoperatively was associated with a lower risk of complications during or immediately following surgery. Seizures occurred only in 1 animal during this time period, but the fact the animals were likely on an anticonvulsant may have decreased necessity for loading or acute initiation of anticonvulsants postoperatively. If animals required loading or acute initiation of an anticonvulsant, this could be a factor that may have contributed to a decrease in mentation of compromised patients and lead to increased risk of aspiration pneumonia (one of the most common complications in this time period). The preoperative seizures were also likely occurring secondary to increased intracranial pressure from the mass effect or other disease process. Theoretically, a craniotomy to remove a mass should help decrease intracranial pressure, which may contribute to a lower risk of complications postoperatively.

Administration of total IV anesthesia with propofol had lower odds of a complication 1 to 10 days after surgery, compared to inhalational anesthesia. This protocol is used to facilitate rapid recovery and decrease intracranial pressure in patients receiving brain surgery. Volatile inhalant agents are reported to interfere with cerebral blood flow regulation, which can lead to an increase in intracranial pressure and decreased cerebral perfusion.22,24,25 Significant increases in intracranial pressure have been reported in animals with intracranial masses and low doses of volatile anesthetic.14 Therefore, it is reasonable to deduce that the administration of total IV anesthesia could have led to our observed lower odds of complication during the postoperative period in these patients. Despite adjustment for this variable, patients who were not fed until 24 hours surgery had 4 times higher odds of complications during this same time period. The clinical reasons for withholding enteral nutrition were not available in the data provided. We suspect that this may have been related to the fact that the patients were too obtunded or sedate to be offered food within the first 24 hours after surgery. Animals that were too sedate may have suffered from increased cranial pressure, substantial hemorrhage, seizures, or other clinical signs related to a complicated recovery. These clinical signs may be taken into account when prognosticating postoperative recovery. Given this potential confounding effect, we cannot make recommendations from this study as to whether feeding should be early or delayed.

Administration of fentanyl postoperatively was associated with higher odds of complications > 10 days after surgery. The most common complications occurring in this period were seizures and neurologic deficits. It may be that this could be a marker of disease severity. If a surgeon performed a very invasive surgery, it may be more likely that they would prescribe fentanyl postoperatively compared to other opioids as boluses or no opioid protocols. According to previous studies,22,24,25 fentanyl is typically considered a favorable opioid due to its rapid onset, short half-life, and pure μ receptor agonist characteristics. Remifentanil is a synthetic full µ-agonist opioid. It has a rapid onset and ultrashort duration due to its clearance by plasma esterases. This makes it ideal for total IV anesthesia. It was reported to be used successfully for a craniectomy procedure in a dog when used with alfaxalone.25

The mortality rate of patients undergoing cranial surgery in our study was 14.5% within 10 days after surgery. This mortality rate was consistent with previous reports. Gordon et al15 reported a mortality rate of 19% for 42 cats underdoing craniotomy for the treatment of cerebral meningioma. Forterre et al5 reported 1 death of 6 cats (16.7%) undergoing craniotomy for tentorial meningiomas. Glass et al21 reported no deaths with a modified bilateral transfrontal sinus approach in 5 dogs. Cameron et al1 reported 7 cats out of 121 (6%) died after undergoing excision of intracranial meningiomas. There is a deficit of published literature reviewing the mortality rate of intracranial surgery in dogs. One publication by Forward et al12 included a larger cohort of patients and reported the death of 4 (8%) dogs at the time of discharge after intracranial surgery. One dog did not survive the immediate postoperative period.12 The present study offers a larger cohort of case numbers for comparison.

Aspiration pneumonia is a potentially lethal postoperative complication for cranial surgery in small animals.4,7,12,23 In humans, risk factors for aspiration pneumonia after neurosurgery include gastrointestinal disease, anesthesia, decreased consciousness, neuromuscular disease, and feeding tubes.5 Aspiration pneumonia may progress to acute respiratory distress syndrome and subsequent respiratory failure. In this study, due to the retrospective nature, the diagnosis of aspiration pneumonia was based on radiographic reports and clinical signs. Results of blood gas analysis and WBC counts postoperatively were not consistently available in the medical records. We reported aspiration pneumonia in 9.7% (16/165) of cases as determined by use of thoracic radiographs within 10 days of surgery. We did not find an association between aspiration pneumonia and death postoperatively in the multivariable analysis, but animals that experienced respiratory compromise did have increased odds of death. The lack of association with aspiration pneumonia is contradictory to previous publications.9,15 A previous report9 of pneumonia after cranial surgery in dogs revealed a prevalence of 24.5% and a resultant high mortality rate (5/7 animals died), whereas a more recent publication4 cites only 3.8% of cases developing aspiration pneumonia postoperatively. Potential reasons for these conflicting findings could be that patients with radiographic evidence of aspiration pneumonia may have been mildly affected or detected early due to increased awareness of this complication following cranial surgery, thus allowing rapid administration of appropriate antimicrobial treatment that could have led to better outcomes in many patients. It was possible that there was a subset of the patients with aspiration pneumonia that also developed a severe complication such as acute respiratory distress syndrome leading to respiratory compromise and potentially death. We did not specifically try to identify patients with acute respiratory distress syndrome in the present study given the retrospective nature and requirement for fulfillment of 5 criteria for diagnosis based on a recent veterinary consensus.26

Study limitations to consider when interpreting this study include the fact this was a retrospective study that relied on assessment of medical records from different institutions. This could have introduced variability in diagnostic and therapeutic approaches. In addition, it is possible that patients lost to follow-up may have died due to their disease process, resulting in an underestimation of postoperative mortality rates. Necropsy results were not available for most patients; therefore, an accurate cause of death could not be determined in every case. However, despite these limitations with rare diseases and treatments, this is often a paucity of prospective clinical trials, and retrospective multicenter observational studies play a role in informing clinical practice and future clinical trials.

In summary, primary CNS neoplasia was the most common indication for cranial surgery in this study population. The mortality rate was 12.1% (20/165) within 10 days of surgery in the present study of dogs and cats undergoing cranial surgery. Surgical approach, preoperative seizures, and administration of fentanyl postoperatively were associated with complications during surgery and within 24 hours postoperatively. Total IV anesthesia with propofol and timing of feeding were associated with odds of complications within 10 days of surgery. Additional prospective investigation is needed to further assess the effect of total IV anesthesia with propofol, use of postoperative fentanyl, and optimal timing of feeding to mitigate risks of complications in animals receiving cranial surgery.

Acknowledgments

No third-party funding or support was received in connection with this study or the writing or publication of the manuscript. The authors declare that there were no conflicts of interest.

References

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    Warne LN, Beths T, Fogal S, Bauquier SH. The use of alfaxalone and remifentanil total intravenous anesthesia in a dog undergoing a craniectomy for tumor resection. Can Vet J. 2014;55(11):10831088.

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    Wilkins PA, Otto CM, Baumgardner JE, et al. Acute lung injury and acute respiratory distress syndrome in veterinary medicine: consensus definitions: The Dorothy Russell Havemeyer Working Group on ALI and ARDS in Veterinary Medicine. J Vet Emerg Crit Care (San Antonio). 2007;17(4):333339.

    • Search Google Scholar
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  • 1.

    Cameron S, Rishniw M, Miller A, Sturges B, Dewey CW. Characteristics and survival of 121 cats undergoing excision of intracranial meningiomas (1994–2011). Vet Surg. 2015;44(6):772776.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 2.

    Schatzberg SJ, Nghiem PP. Medical conditions of the nervous system. In: Tobias K, Johnston S, eds. Veterinary Surgery: Small Animal. Saunders; 2011:388409.

    • Search Google Scholar
    • Export Citation
  • 3.

    Talarico LR, Dewey CW. Intracranial neoplasia. In: Tobias K, Johnston S, eds. Veterinary Surgery: Small Animal. Saunders; 2011:511516.

    • Search Google Scholar
    • Export Citation
  • 4.

    Schatzberg SJ, Nghiem PP. Anesthesia for intracranial surgery. In: Tobias K, Johnston S, eds. Veterinary Surgery: Small Animal. Saunders; 2011:388409.

    • Search Google Scholar
    • Export Citation
  • 5.

    Forterre F, Fritsch G, Kaiser S, Matiasek K, Brunnberg L. Surgical approach for tentorial meningiomas in cats: a review in six cases. J Feline Med Surg. 2006;8(4):227233.

    • Search Google Scholar
    • Export Citation
  • 6.

    Snyder JM, Shofer FS, Van Winkle TJ, Massicotte C. Canine intracranial primary neoplasia: 173 cases (1986–2003). J Vet Intern Med. 2006;20(3):669675.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 7.

    Campoy L, Martin-Flores M. Anesthesia for intracranial surgery. In: Tobias K, Johnston S, eds. Veterinary Surgery: Small Animal. Saunders; 2011:530536.

    • Search Google Scholar
    • Export Citation
  • 8.

    Boston SE. Craniectomy and orbitectomy in dogs and cats. Can Vet J. 2010;51(5):537540.

  • 9.

    Fransson BA, Bagley RS, Gay JM, et al. Pneumonia after intracranial surgery in dogs. Vet Surg. 2001;30(5):432439.

  • 10.

    Greco JJ, Aiken SA, Berg JM, Monette S, Bergman PJ. Evaluation of intracranial meningioma resection with a surgical aspirator in dogs: 17 cases (1996–2004). J Am Vet Med Assoc. 2006;229(3):394400.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 11.

    Javaheri S, Corbett WS, Simbartl LA, Mehta S, Khosla A. Different effects of omeprazole and Sch 28080 on canine cerebrospinal fluid production. Brain Res. 1997;754(1-2):321324.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 12.

    Forward AK, Volk HA, De Decker S. Postoperative survival and early complications after intracranial surgery in dogs. Vet Surg. 2018;47(4):549554.

  • 13.

    Dewey CW. Surgery of the brain. In: Fossum TW, Dewey CW, Horn CV, et al., eds. Small Animal Surgery. 4th ed. Mosby; 2012:14381465.

  • 14.

    De Decker S, Davies E, Benigni L, et al. Surgical treatment of intracranial epidermoid cyst in a dog: intracranial epidermoid cyst. Vet Surg. 2012;41(6):766771.

    • Search Google Scholar
    • Export Citation
  • 15.

    Gordon LE, Thacher C, Matthiesen DT, Joseph RJ. Results of craniotomy for the treatment of cerebral meningioma in 42 cats. Vet Surg. 1994;23(2):94100.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 16.

    Kohler RJ, Arnold SA, Eck DJ, Thomson CB, Hunt MA, Pluhar GE. Incidence of and risk factors for major complications or death in dogs undergoing cytoreductive surgery for treatment of suspected primary intracranial masses. J Am Vet Med Assoc. 2018;15:253(12):15941603.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 17.

    Niebauer GW, Dayrell-Hart BL, Speciale J. Evaluation of craniotomy in dogs and cats. J Am Vet Med Assoc. 1991;198(1):8995.

  • 18.

    Rossmeisl JH, Pancotto TE. Tumors of the nervous system. In: Vail DM, Thamm DH, Liptak JM, eds. Withrow and MacEwen’s Small Animal Clinical Oncology. 6th ed. Saunders; 2016:657665.

    • Search Google Scholar
    • Export Citation
  • 19.

    Holmes ME, Keyerleber MA, Faissler D. Prolonged survival after craniectomy with skull reconstruction and adjuvant definitive radiation therapy in three dogs with multilobular osteochondrosarcoma. Vet Radiol Ultrasound. 2019;60:447455.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 20.

    Bordelon JT, Rochat MC. Use of a titanium mesh for cranioplasty following radical rostrotentorial craniectomy to remove an ossifying fibroma in a dog. J Am Vet Med Assoc. 2007;231(11):16921695.

    • Search Google Scholar
    • Export Citation
  • 21.

    Glass EN, Kapatkin A, Vite C, Steinberg SA. A modified bilateral transfrontal sinus approach to the canine frontal lobe and olfactory bulb: surgical technique in five cases. J Am Anim Hosp Assoc. 2000;36(1):4350.

    • Search Google Scholar
    • Export Citation
  • 22.

    Raisis AL, Leece EA, Platt SR, Adams VJ, Corletto F, Brearley J. Evaluation of an anaesthetic technique used in dogs undergoing craniectomy for tumour resection. Vet Anaesth Analg. 2007;34(3):171180.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 23.

    Fusco JV, Hohenhaus AE, Aiken SW, Joseph RJ, Berg JM. Autologous blood collection and transfusion in cats undergoing partial craniectomy. J Am Vet Med Assoc. 2000;216(10):15841588.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 24.

    Amengual M, Leigh H, Rioja E. Postoperative respiratory effects of intravenous fentanyl compared to intravenous methadone in dogs following spinal surgery. Vet Anaesth Analg 2017;44(5):10421048.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 25.

    Warne LN, Beths T, Fogal S, Bauquier SH. The use of alfaxalone and remifentanil total intravenous anesthesia in a dog undergoing a craniectomy for tumor resection. Can Vet J. 2014;55(11):10831088.

    • Search Google Scholar
    • Export Citation
  • 26.

    Wilkins PA, Otto CM, Baumgardner JE, et al. Acute lung injury and acute respiratory distress syndrome in veterinary medicine: consensus definitions: The Dorothy Russell Havemeyer Working Group on ALI and ARDS in Veterinary Medicine. J Vet Emerg Crit Care (San Antonio). 2007;17(4):333339.

    • Search Google Scholar
    • Export Citation

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