A 6-year-old 2.08-kg (4.58-lb) neutered male Lionhead-mix pet rabbit (Oryctolagus cuniculus) was examined because of sneezing and increased respiratory effort. The only known medical history was an episode of gastrointestinal tract stasis—evidenced by a decreased appetite and smaller than usual fecal pellets at the age of 3 years—that had resolved with supportive care. There was no known history of trauma. Approximately 1 month prior to the initial evaluation, the rabbit started sneezing and developed bilateral serous nasal discharge after the owner changed the commercial brand of timothy hay provided to the rabbit. During this period, the owner also noted that the rabbit had intermittent increased respiratory effort, particularly after strenuous exercise. The rabbit was otherwise healthy and eating normally.
On initial evaluation, the rabbit was bright, alert, and responsive. Respiratory rate and effort were slightly increased, compared with findings in healthy rabbits in general. Sneezing or nasal discharge was not observed. Results of the remainder of the physical examination, CRC, and plasma biochemical analysis were unremarkable. Well-formed fecal pellets were expelled by the rabbit during the examination. Radiographic examination of the thorax (including the cranial portion of the abdomen) was performed, and right lateral and ventrodorsal radiographic views were obtained. Examination of these images revealed a smoothly marginated fat tissue opacity within the caudal portion of the thorax, particularly the right dorsal hemithoracic region. Mediastinal shift to the left and loss of visualization of the diaphragmatic line were evident. An ovoid soft tissue opacity within the fat tissue opacity in the right hemithorax at the level of the T9 through T11 vertebrae was detected. The left kidney had a normal appearance and anatomic location, but the right kidney was not visible in its expected location. The structure observed as the ovoid soft tissue opacity was considered to be the right kidney displaced into the thoracic cavity. In addition, most of the intestines were displaced toward the right side of the abdomen on the ventrodorsal radiographic view (Figure 1). A presumptive radiographic diagnosis of congenital diaphragmatic retroperitoneal perirenal fat and right kidney herniation was made, given the lack of known previous trauma; however, trauma of which the owner was unaware could not be ruled out. Congenital, rather than acquired, diaphragmatic hernia was more probable because there was no history of previous trauma for this rabbit. Further diagnostic imaging with CT and exploratory celiotomy were declined by the owner.
Right lateral (A) and ventrodorsal (B) radiographic views of the thorax and cranial portion of the abdomen of a 6-year-old Lionhead-mix rabbit (Oryctolagus cuniculus) that was evaluated because of sneezing and increased respiratory effort. Notice a smoothly marginated fat tissue opacity (asterisks) within the right dorsal hemithoracic region, left mediastinal shift, and loss of visualization of the diaphragmatic line. An ovoid soft tissue opacity (arrowheads) within the fat tissue opacity is located in the right hemithorax at the level of the T9-T11 vertebrae. In addition, the left kidney is visible in its normal anatomic location, but the right kidney is absent from its expected location.
Citation: Journal of the American Veterinary Medical Association 248, 12; 10.2460/javma.248.12.1399
Right lateral (A) and ventrodorsal (B) radiographic views of the thorax and cranial portion of the abdomen of a 6-year-old Lionhead-mix rabbit (Oryctolagus cuniculus) that was evaluated because of sneezing and increased respiratory effort. Notice a smoothly marginated fat tissue opacity (asterisks) within the right dorsal hemithoracic region, left mediastinal shift, and loss of visualization of the diaphragmatic line. An ovoid soft tissue opacity (arrowheads) within the fat tissue opacity is located in the right hemithorax at the level of the T9-T11 vertebrae. In addition, the left kidney is visible in its normal anatomic location, but the right kidney is absent from its expected location.
Citation: Journal of the American Veterinary Medical Association 248, 12; 10.2460/javma.248.12.1399
Right lateral (A) and ventrodorsal (B) radiographic views of the thorax and cranial portion of the abdomen of a 6-year-old Lionhead-mix rabbit (Oryctolagus cuniculus) that was evaluated because of sneezing and increased respiratory effort. Notice a smoothly marginated fat tissue opacity (asterisks) within the right dorsal hemithoracic region, left mediastinal shift, and loss of visualization of the diaphragmatic line. An ovoid soft tissue opacity (arrowheads) within the fat tissue opacity is located in the right hemithorax at the level of the T9-T11 vertebrae. In addition, the left kidney is visible in its normal anatomic location, but the right kidney is absent from its expected location.
Citation: Journal of the American Veterinary Medical Association 248, 12; 10.2460/javma.248.12.1399
The rabbit's sneezing, nasal discharge, and increased respiratory effort that developed after introduction of the new brand of hay was most likely a result of upper airway allergic reaction or irritation. The owner switched back to the former brand of hay, and the rabbit was restricted from strenuous exercise and monitored for any deterioration in its condition. The owner reported that sneezing and serous nasal discharge did not recur after switching back to the former brand of hay. However, intermittent increased respiratory effort was still present.
Nine months later, the rabbit was reexamined because of decreased appetite and activity level, restlessness, and increased frequency of episodes of respiratory effort over the preceding few weeks. The owner reported providing foster care to another neutered male rabbit over the past 3 months. During that period, the owner noted that the resident rabbit was exceptionally excited and hyperactive when in the presence of the foster rabbit. Physical examination findings were unremarkable except for an increased respiratory rate and effort and a slightly decreased body weight (1.95 kg [4.29 lb]). Results of CBC and plasma biochemical analysis were also unremarkable. Right and left lateral and ventrodorsal thoracic radiography revealed increased fat tissue opacity volume within the thorax, decreased lung aeration, caudal displacement of the liver, and further craniomedial displacement of the right kidney, compared with findings at the initial evaluation (Figure 2). Radiographic findings suggested further herniation of the retroperitoneal perirenal fat. On the basis of the rabbit's clinical status, physical examination results, and radiographic findings, an exploratory celiotomy was performed.
Left lateral (A) and ventrodorsal (B) radiographic views of the thorax of the rabbit in Figure 1 obtained 9 months after the initial evaluation. Compared with the earlier radiographic findings, there is evidence of increased fat tissue opacity volume (asterisks) within the thorax, decreased lung aeration, caudal displacement of the liver, and further craniomedial displacement of the right kidney (arrowheads), suggesting further herniation into the thoracic cavity.
Citation: Journal of the American Veterinary Medical Association 248, 12; 10.2460/javma.248.12.1399
Left lateral (A) and ventrodorsal (B) radiographic views of the thorax of the rabbit in Figure 1 obtained 9 months after the initial evaluation. Compared with the earlier radiographic findings, there is evidence of increased fat tissue opacity volume (asterisks) within the thorax, decreased lung aeration, caudal displacement of the liver, and further craniomedial displacement of the right kidney (arrowheads), suggesting further herniation into the thoracic cavity.
Citation: Journal of the American Veterinary Medical Association 248, 12; 10.2460/javma.248.12.1399
Left lateral (A) and ventrodorsal (B) radiographic views of the thorax of the rabbit in Figure 1 obtained 9 months after the initial evaluation. Compared with the earlier radiographic findings, there is evidence of increased fat tissue opacity volume (asterisks) within the thorax, decreased lung aeration, caudal displacement of the liver, and further craniomedial displacement of the right kidney (arrowheads), suggesting further herniation into the thoracic cavity.
Citation: Journal of the American Veterinary Medical Association 248, 12; 10.2460/javma.248.12.1399
The rabbit underwent preoxygenation in a chamber for 10 minutes prior to administration of pethidine hydrochloridea (5 mg/kg [2.27 mg/lb], IM) as a preanesthetic medication. Oxygenation was continued while the sedative was taking effect. Anesthesia was rapidly induced with midazolamb (0.3 mg/kg [0.14 mg/lb], IV) and propofolc (3 mg/kg [1.36 mg/lb], IV). The rabbit was then immediately blindly intubated, and inhalation anesthesia was maintained with isofluraned (2% to 3%) in oxygen. Additional perioperative pain management treatments included a constant rate infusion of fentanyle (10 μg/kg/h [4.55 μg/lb/h]) and a constant rate infusion of a mixture of lidocaine hydrochloridef (0.6 mg/kg/h [0.27 mg/lb/h]) and ketamine hydrochlorideg (0.6 mg/kg/h). Lactated Ringer solutionh (10 mL/kg/h, IV) was administered throughout the surgery. Hair on the caudal aspect of the rabbit's thorax and abdomen was clipped, and the skin was aseptically prepared. The rabbit was positioned in dorsal recumbency with the head toward the elevated end of the operating table; the table was tilted at approximately 30°. A ventral midline celiotomy from the xiphoid process to the umbilicus was performed. The abdomen was explored, and the right kidney and most of the perirenal fat were found to be displaced into the thorax through an elliptical tear in the right dorsal tendinous portion of the diaphragm (Figure 3). The edges of the diaphragmatic tear were smooth with no evidence of fibrosis. The herniated perirenal fat was neither devitalized nor adherent to any nearby structures. After enlargement of the diaphragmatic hernia ring, the right kidney and the perirenal fat were replaced back into the retroperitoneal space. A diaphragmatic herniorrhaphy was performed with 3–0 nylon suturei in a simple continuous pattern. Prior to completion of the last knot of the closure, air within the thoracic cavity was evacuated by means of a syringe connected to a 3-way stopcock with an extension tube. The abdominal muscle was closed with 3–0 polyglycolide suturej in a simple continuous pattern. The skin incision was closed with 4–0 polyglactin suturek in an intradermal pattern. The rabbit recovered from anesthesia uneventfully. Analgesia was provided for 72 hours following the procedure by administration of buprenorphine hydrochloridel (30 μg/kg [13.64 μg/lb], IV, q 8 h for 2 days), meloxicamm (0.5 mg/kg [0.23 mg/lb], PO, q 24 h for 3 days), and a constant rate infusion of lidocaine hydrochloridef (0.6 mg/kg/h for 2 days). The rabbit was discharged from the hospital 5 days after surgery. No further clinical signs were observed during the following 16-month period.
Intraoperative photograph of the right cranial quadrant of the abdomen of the rabbit in Figure 1. A defect (arrowheads) is present in the right dorsal tendinous portion of the diaphragm; the edges of the defect are smooth with no fibrotic tissue. Retroperitoneal perirenal fat (asterisk) has protruded into the thoracic cavity through the diaphragmatic defect.
Citation: Journal of the American Veterinary Medical Association 248, 12; 10.2460/javma.248.12.1399
Intraoperative photograph of the right cranial quadrant of the abdomen of the rabbit in Figure 1. A defect (arrowheads) is present in the right dorsal tendinous portion of the diaphragm; the edges of the defect are smooth with no fibrotic tissue. Retroperitoneal perirenal fat (asterisk) has protruded into the thoracic cavity through the diaphragmatic defect.
Citation: Journal of the American Veterinary Medical Association 248, 12; 10.2460/javma.248.12.1399
Intraoperative photograph of the right cranial quadrant of the abdomen of the rabbit in Figure 1. A defect (arrowheads) is present in the right dorsal tendinous portion of the diaphragm; the edges of the defect are smooth with no fibrotic tissue. Retroperitoneal perirenal fat (asterisk) has protruded into the thoracic cavity through the diaphragmatic defect.
Citation: Journal of the American Veterinary Medical Association 248, 12; 10.2460/javma.248.12.1399
Discussion
Diaphragmatic hernias are classified as traumatic and congenital hernias.1,2 In dogs and cats, traumatic herniation is the most common cause of diaphragmatic hernias, with congenital herniation occurring in only 15% of cases.3,4 In descending order, the organs that are most frequently herniated through the diaphragm are the liver, small intestine, stomach, spleen, and omentum.3 Diaphragmatic kidney herniation into the thoracic cavity in humans and other animals has rarely been reported.5–8 Diaphragmatic hernia with displacement of a kidney in cats has been described.6,7,9–11 Diaphragmatic hernia in rabbits is a very rare condition. To the authors’ knowledge, there is only 1 case report8 of a diaphragmatic hernia in a rabbit in the veterinary medical literature. In contrast with studies1,12 in dogs and cats that revealed the liver to be the most commonly herniated organ, the aforementioned report8 described radiographic and necropsy findings of diaphragmatic kidney herniation in a rabbit. To our knowledge, this is the first report of clinical diagnosis and surgical management of diaphragmatic retroperitoneal perirenal fat and kidney herniation in a rabbit.
An abrupt increase in intra-abdominal pressure when the glottis is open produces a large pressure gradient between the pleural and peritoneal cavities, which can result in a diaphragmatic hernia.1,2,13 The high pleuroperitoneal pressure gradient may force viscera through congenitally weak or defective areas.2 Sneezing is one of the activities that causes temporary increases in intra-abdominal pressure.14 The sneezing and nasal discharge observed in the rabbit of the present report were most likely a result of nasal mucosal irritation, possibly caused by excessive amounts of dust and scraps from the new brand of hay bought by the owner. For this rabbit, we speculated that sneezing caused sudden increases in intra-abdominal pressure, which resulted in initial diaphragmatic herniation or further herniation of abdominal tissues already present in the thorax. The excitement and hyperactive behavior of the patient toward the foster rabbit were considered to contribute to additional increases in intra-abdominal pressure via increased tension on the abdominal wall muscle. We speculated that additional force was exerted on the herniated viscera, which eventually caused progressive lung collapse and possible bronchial compression.
Radiography is the most useful diagnostic imaging technique for confirming a diagnosis of diaphragmatic hernia.13 If a diagnosis cannot be made from survey radiographic findings, ultrasonography may be performed to obtain additional information.1 Ultrasonography is particularly useful in animals with pleural effusion because fluid is an excellent acoustic window.15 Although rarely indicated, results of diagnostic imaging of the gastrointestinal tract after contrast agent administration may be used to confirm diaphragmatic hernia when the stomach or intestines are involved. Computed tomography can also be used to rapidly obtain accurate information about location, extent, and contents of the hernia. In the case described in the present report, radiographic examination alone provided sufficient evidence to make the diagnosis. Key radiographic signs were fat tissue opacity within the right caudodorsal thoracic region, loss of visualization of the diaphragmatic line, and loss of the right kidney and retroperitoneal perirenal fat from the abdomen. The ovoid soft tissue opacity within the fat tissue opacity was highly suggestive of the right kidney, because that organ could not be detected in its expected anatomic location. Thus, a straightforward diagnosis of right dorsal diaphragmatic retroperitoneal perirenal fat and kidney herniation was made for the rabbit of this report. In contrast with the clinical findings, radiographic detection of a fat tissue opacity suggestive of retroperitoneal fat was not described in the previous report of diaphragmatic kidney herniation in a rabbit.8 In retrospect, the use of ultrasonography in the rabbit of the present report could have been used to further evaluate the herniated renal structure and the patency of the postrenal urinary tract and to confirm the diagnosis.
Anatomically, the abdomen of rabbits is large in comparison with the thoracic cavity16,17 and contains a cecum that holds an enormous amount of ingesta.18 Rabbits may become hypoxemic immediately after induction of anesthesia because of lung collapse caused by abdominal viscera compression against the diaphragm.16 Moreover, oxygenation may also be influenced by body position.19 In the rabbit of the present report, in addition to the aforementioned anatomic effects on ventilation, the herniated right kidney and retroperitoneal perirenal fat contributed additional compression on the lungs and resulted in further lung collapse. Prior to surgery, several measures were undertaken to optimize oxygenation, including administration of oxygen, rapid induction of anesthesia followed by immediate intubation, positioning of the rabbit's head toward the elevated end of the table, and tilting the table to an angle of 30°. Provision of oxygen prior to anesthesia increases the concentration of oxygen stored as functional residual capacity in the lungs20 and may delay desaturation of hemoglobin.21 Prompt establishment of a patent airway via endotracheal tube placement allows controlled ventilation for adequate pulmonary expansion and oxygenation.13,22 Tilting the table to an angle of 30° to 40° and placement of the patient with its head toward the elevated end of the table facilitates gravitation of abdominal viscera caudally out of the thorax,23 which lessens the compressive effect on the lungs and improves visibility of the diaphragm (particularly its dorsal aspect) during surgery.24
Surgical exploration in the rabbit of the present report revealed a tear in the right dorsal tendinous portion of the diaphragm, and the edges of the defect were smooth with no fibrotic scar tissue. In addition, the rabbit had no known history of trauma, and no traumatic lesions were evident on the radiographic views or during the surgical procedure. Thus, a congenital defect rather than trauma was more likely a contributing cause, although unknown traumatic origin could not be completely excluded. In contrast with the finding that the muscular portions of the diaphragm are the most common locations of such a tear,1 a defect in the tendinous portion of the diaphragm was observed in this rabbit. Surgical correction of diaphragmatic hernias is recommended for animals with clinical signs because of the risk of life-threatening respiratory decompensation.13 In the case described in this report, the rabbit underwent surgery because of respiratory compromise and the potential for further herniation over time with possible subsequent ureteral obstruction or rupture. No postoperative complications were observed in this rabbit, and no recurrence of clinical signs was observed during long-term follow-up.
Footnotes
Pethidine hydrochloride injection, Food and Drug Administration Factory for Controlled Drugs, New Taipei City, Taiwan.
Midatin, Nang Kuang, Tainan City, Taiwan.
Fresofol 1%, Fresenius Kabi, Bad Homburg vor der Höhe, Germany.
Isoflurane, Halocarbon Products Corp, River Edge, NJ.
Fentanyl Injection, Food and Drug Administration Factory for Controlled Drugs, New Taipei City, Taiwan.
Xylocaine, Cenexi, Fontenay-sous-Nois, France.
IMALGENE 1000, Merial, Toulouse, France.
L-Ringer, Nang Kuang, Tainan City, Taiwan.
3–0 Nylon, Unik, New Taipei City, Taiwan.
3–0 EU-TEK, Unik, New Taipei City, Taiwan.
4–0 PGVet, MedHarmony, Pittsburgh, Pa.
Temgesic, Reckitt Benckiser Healthcare Ltd, Hull, East Yorkshire, England.
Achefree, Swiss Pharmaceutical Co Ltd, Tainan City, Taiwan.
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