Five dogs that ranged in age from 4 to 10 years (median age, 9 years) and weighed between 8.5 and 51.0 kg (18.7 and 112.2 lb) with undefined nasal masses were evaluated between 2012 and 2014 at the veterinary teaching hospital of Texas A&M University. All dogs had undergone CT of the head and nasal biopsy via a rostral rhinoscopic or unaided (blind) approach within the previous 3 weeks at the teaching hospital (2 dogs) or other referral hospitals (3 dogs). Clinical signs at evaluation included open-mouth breathing, sneezing, or unilateral epistaxis. Although the mass lesions identified via CT appeared extensive and had criteria of aggressive or malignant disease processes such as bone lysis, results of histologic evaluation of biopsy specimens suggested the nature of the lesions was inflammatory, necrotic, or hemorrhagic and those specimens were therefore believed to poorly represent the underlying disease processes.
Because of the discordance between imaging and biopsy results, a decision was made to collect additional biopsy specimens of nasal mass tissue by means of a frameless CTSBS in a manner similar to that reported for collection of brain biopsy specimens from dogs at our institution.1 For the procedure, each dog was anesthetized with an injectable agent, the choice of which was at the discretion of the attending anesthesiologist. An endotracheal tube was placed, and anesthesia was maintained by administration of an inhalant agent (isoflurane or sevoflurane).
In preparation for CT imaging, the head of each dog was secured to a custom-built stereotactic table with acrylic predrilled bite plates and thermoplastic puttya that conformed to the dentition of the dog (Figure 1). Six fiducial markers of various heights were secured to the bite plate. The head, from the nasal planum to the caudal aspect of the C2 vertebral body, was imaged with a 40-slice CT scanner,b with a slice thickness of 0.6 mm and interval (distance between 2 consecutive reconstructed images) of 0.3 mm (210 kV; 110 to 248 mA). Computed tomographic images were reconstructed in a bone algorithm in the transverse plane. The fiducialized CT images were imported into stereotactic softwarec installed on a diagnostic workstation. After image importation, a referenced image reconstruction was created.
After CT was finished and prior to transfer of dogs to the surgical suite, primary hemostasis was evaluated by measurement of buccal mucosa bleeding time with a 1.0 × 3.5-mm lancet device.d Results were considered unremarkable for all dogs (< 4 minutes and 30 seconds).2 Skin over the nasal passages and maxilla was shaved of hair, and a chlorhexidine solution was applied for preliminary antisepsis. Cefazolin (22 mg/kg [10 mg/lb], IV) was administered before the CTSBS procedure and then every 2 hours until the procedure was over. Each dog was moved to the surgical suite and positioned in front of an infrared camera.c
A digital reference frame was attached to the CT head holder, and fiducial markers affixed to the bite plate were electronically registered into the CTSBS by use of a standard probe with reflective spheres (Figure 1). The surgical field was draped in a standard fashion. A 2-mm biopsy rongeure with attached reflective spheres was electronically registered into the system. Registration of the biopsy rongeur allowed the clinician to identify the location of the instrument in relation to the nasal lesion as well as to plan the skin incision site and biopsy trajectory. An approximately 1-cm incision was made through the skin and subcutaneous tissues with a No. 11 scalpel blade to expose the underlying bone. The periosteum was reflected with periosteal elevators. Biopsy site and trajectory were established by placement of the registered biopsy rongeur on the nasal bone, with concurrent examination of the CT reconstruction (Figure 2). Biopsy site was chosen on the basis of mass extent, with care to avoid critical structures (eg, vessels or cribriform plate). A 3-mm burr hole was drilled with a pneumatic bone drill through the exposed nasal or maxillary bone. Multiple specimens of mass tissue were collected through the single created burr hole with the registered biopsy rongeur in a freehand manner while the rongeur trajectory was visually monitored via the stereotactic software. A modified geological core biopsy technique was used, in which specimens were collected from the near edge, center, and distant edge of the mass; for all dogs, at least 2 core specimens were obtained by altering rongeur trajectory through the burr.3 Factors including sizes of the mass and nasal passages, proximity of the mass to vital structures, and intraoperative evaluation of cytologic results influenced whether > 2 core specimens were obtained.
Biopsy specimens were placed in 10% formalin solution and submitted for histologic evaluation. When intraoperative cytologic findings suggested the presence of neutrophilic or pyogranulomatous inflammation (2 dogs), specimens were also prepared for bacterial and fungal culture. Hemorrhage from the burr hole was controlled with suction. Bone wax was placed in the burr hole to create a seal between the nasal cavity and subcutaneous tissues to prevent subcutaneous emphysema. The subcutaneous tissues and skin over the burr hole were closed in a routine manner. Various opiates were administered IV for immediate postoperative pain relief. Tramadol (2 to 4 mg/kg [0.9 to 1.8 mg/lb], PO, q 8 h for 7 days) was provided for at-home pain control.
Median duration of imaging for the CTSBS procedure was 35 minutes (range, 15 to 40 minutes), which included the time required for transportation from the anesthesia suite to the imaging center, acquisition of CT scans, and transportation to the surgical suite. Mass lesions were identified in all 5 dogs, with 4 dogs having a unilateral lesion and 1 having a bilateral lesion. Four dogs had a lesion at the caudal aspect of the nasal cavity, and 1 dog had a lesion at the rostral to mid aspect of the nasal cavity. Invasion of the cribriform plate was detected in 2 dogs, and 1 of those dogs also had invasion into the maxillary recess and frontal sinus.
Biopsy specimen collection, including surgical site preparation, electronic patient registration, draping, electronic instrument registration, and the actual biopsy procedure, required a median of 55 minutes (range, 38 to 84 minutes). A median of 8 biopsy specimens was collected per dog (range, 6 to 14). A board-certified clinical pathologist examined impression smears of biopsy specimens during the CTSBS procedure. If results of cytologic evaluation suggested that the biopsy specimens collected were of diagnostic quality, then specimen collection was suspended. Size of biopsy specimen varied depending on the friable nature of the mass; most specimens were approximately 3 × 2 × 1 mm, and the largest collected was 1 × 1 × 15 mm. Blood loss was estimated at < 10 mL for all dogs. Median total anesthetic duration was 285 minutes (range, 135 to 315 minutes).
All dogs were discharged from the hospital within 24 hours after the CTSBS procedure. Postoperative hemorrhage and emphysema were not reported, and all skin incisions healed without complication.
Histologic evaluation of biopsy specimens from 3 of the 5 dogs revealed findings suggestive of malignant neoplasia (Table 1). For 1 dog, CTSBS results suggested a mild mixed inflammatory response, whereas initial biopsy results suggested lymphoplasmacytic inflammation. However, the prebiopsy CT scan had revealed a large aggressive nasal mass involving the left and right nasal cavities that extended into the right maxillary recess and frontal sinus of that dog. Severe lysis of the right maxillary bone was also evident. No postbiopsy CT scan was performed on the area from which the biopsy specimen was collected.
Clinical findings associated with nasal masses in 5 dogs that underwent CT evaluation of the head and nasal biopsy via a rostral rhinoscopic or unaided (blind) approach, followed 3 weeks later by a CTSBS procedure.
|Dog||CT results||Initial biopsy results||CTSBS collection site||CTSBS results|
|1||23 × 19 × 43-mm soft tissue mass in the left nasal cavity, with destruction of the cribriform plate||Neutrophilic inflammation||Dorsal midline region over caudal portion of nasal bone||Hemangiopericytoma|
|2||33 × 28 × 92-mm soft tissue mass occupying the right nasal cavity, with extension into the right frontal sinus; cribriform plate involvement suspected||Inflamed granulation tissue or an inflamed vascular tumor (first biopsy procedure); necrosis (second biopsy procedure)||Right dorsal paramedian region over caudal maxillary bone||Undifferentiated sarcoma|
|3||44 × 27 × 82-mm space-occupying soft tissue mass occupying most of the right nasal cavity||Lymphoplasmacytic and eosinophilic inflammation||Right dorsal paramedian region over caudal maxillary bone||Chondrosarcoma|
|4||18 × 34 × 61-mm bilateral soft tissue mass of entire nasal cavity (worse on right), with facial bone lysis||Lymphoplasmacytic inflammation||Right dorsal paramedian region over caudal maxillary bone||Mild mixed-cell inflammation|
|5||18 × 23 × 36-mm soft tissue mass of the right caudal nasal cavity||Vascular hamartoma||Right dorsal paramedian region over caudal maxillary bone||Vascular hamartoma|
In another dog, 2 masses were identified. The most rostrally located mass was situated at the nasal planum and was diagnosed by the referring veterinarian as squamous cell carcinoma on the basis of results of cytologic evaluation. A second and larger mass was identified incidentally on CT scan and was associated with the ventral mid to caudal aspect of the right nasal passage. Focal turbinate destruction was identified in the region of the second mass; however, there was no evidence of maxillary bone destruction. The referring veterinarian had obtained a biopsy specimen of this second mass via a rostral rhinoscopic approach. Malignant neoplasia was not identified as a result of this initial biopsy. Histologic findings for the initial biopsy specimen suggested a vascular hamartoma or arterial-venous nevus, and subsequent use of the CTSBS confirmed this diagnosis for the second mass. For the dog with hamartoma, a CT scan of the nasal cavity was performed 2 weeks after the CTSBS procedure was performed. That CT scan revealed that the biopsy specimens collected via CTSBS guidance had been collected directly from the center of the second mass (Figure 3). This dog was the only patient in which a postoperative CT scan was performed.
Computed tomography–guided stereotactic biopsy system
VP Mix, Henry Schein Inc, Melville, NY.
Siemens Somatom Definition AS, Siemens, Malvern, Pa.
Radionics OmniSight EXcell, Integra Radionics, Burlington, Mass.
Surgicutt Junior, ITC, Edison, NJ.
2-mm cup 6-inch Grasping & Biopsy Roungeur, Sontec Instruments, Centennial, Colo.
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