Diagnosis and surgical treatment of a malignant trichoepithelioma of the ear canal in a pet rabbit (Oryctolagus cuniculus)

• Autores: Casey Budgeon
• Localización: JAVMA: Journal of the American Veterinary Medical Association, ISSN-e 0003-1488, Vol. 245, Nº. 2, 2014, págs. 227-231
• Idioma: inglés
• Texto completo no disponible (Saber más ...)
• Resumen

  • Case Description—A 10-year-old spayed female Holland Lop–mix pet rabbit (Oryctolagus cuniculus) was evaluated because of purulent-hemorrhagic discharge from the right ear canal and a suspected mass within that ear canal.

    Clinical Findings—Results of contrast-enhanced CT, video otoscopy, and histologic examination of endoscopic tissue biopsy samples indicated severe otitis media and externa and a benign trichoepithelioma of the right ear canal.

    Treatment and Outcome—Total ear canal ablation and lateral bulla osteotomy were performed. Histologic examination of a surgical biopsy sample of the mass indicated malignant trichoepithelioma. Tumor recurrence was detected 22 weeks after surgery. The rabbit was euthanized 33 weeks after surgery because of the large size of the recurrent tumor and declining quality of life. Necropsy findings indicated a malignant trichoepithelioma with local and lymphatic invasion into the right mandibular lymph node.

    Clinical Relevance—This was the first report of the clinical diagnosis, surgical treatment, and outcome for a domestic rabbit with a diagnosis of a malignant trichoepithelioma of the ear canal and associated otitis media and externa. Neoplasia should be included as a differential diagnosis for pet rabbits with otitis externa and media. Although such tumors are typically benign, trichoepitheliomas in rabbits can be malignant. Computed tomography and histologic examination of tissue samples were useful diagnostic techniques, but histologic examination of an endoscopic biopsy sample did not allow identification of malignant characteristics of the trichoepithelioma.

    A 10-year-old spayed female Holland Lop–mix pet rabbit (Oryctolagus cuniculus), with a body weight of 2.7 kg (5.94 lb), was referred to the University of Wisconsin Veterinary Medical Teaching Hospital for evaluation of purulent-hemorrhagic discharge from the right ear canal and a suspected mass in that ear canal. Initial physical examination revealed that the right ear was inflamed and signs of pain were detected during palpation. A small amount of dried blood and purulent discharge was detected on the pinna and the opening of the right ear canal (Figure 1). The left ear appeared clinically normal with no discharge. Results of the remainder of the physical examination, plasma biochemical analyses, and CBC were unremarkable.1 The patient was anesthetized, and contrast-enhanced CT of the head was performed. The rabbit was premedicated with butorphanola (0.25 mg/kg [0.11 mg/lb], IM) and midazolamb (0.5 mg/kg [0.23 mg/lb], IM). Isoflurane was administered by mask for anesthetic induction and maintenance. Transverse plane CT images were obtained before and after IV administration of iodinated contrast mediumc (2.2 mL of iohexol/kg [1 mL/lb]; 300 mg of iodine/mL). The CT findings were consistent with right chronic otitis media. In addition, there was an irregular polypoid (diameter, 1.5 cm) soft tissue mass containing focal regions of heterogeneous mineralization and a contrast-enhancing rim extending laterally from the distal aspect of the right ear canal (Figure 2). Results of video otoscopyd,e indicated accumulation of purulent material in the right ear canal and a broad-based poorly defined mass in the vertical portion of that ear canal. The mass obliterated the anatomic architecture of the right ear canal and occluded the vertical portion of that ear canal. Examination of an endoscopic tissue biopsy samplef (submitted in neutral-buffered 10% formalin) revealed a benign trichoepithelioma characterized by epithelial aggregates with various degrees of infundibular, isthmus, and matrical differentiation (Figure 3). Results of bacterial culture indicated moderate mixed growth of gram-positive bacteria; all of these bacteria were susceptible to enrofloxacin. Before those results were available, treatment was started including enrofloxacing (10 mg/kg [4.55 mg/lb], PO, q 12 h), penicillin G procaine and penicillin G benzathineh (50,000 U/kg [22,727 U/lb], SC, q 5 d [total number of doses administered = 6]), and meloxicami (0.3 mg/kg [0.14 mg/lb], PO, q 12 h). In addition, topical treatments included corticosteroid and antimicrobial otic dropsj (administered in the right ear, q 24 h, for 14 days). The owners were counseled regarding surgical, medical, and palliative treatment options.

    View larger version(132K) Figure 1— Photographs of a trichoepithelioma in the external right ear canal of a 10-year-old spayed female Holland Lop–mix domestic rabbit (Oryctolagus cuniculus) evaluated because of purulent-hemorrhagic discharge from the right ear canal and a suspected mass in that ear canal. A—Photograph of a mass in the external ear canal detected during physical examination. B—Otoscopic image of the external ear canal. A broad-based mass was detected; histologic examination of an endoscopic biopsy sample indicated a benign trichoepithelioma. C—Photograph of purulent discharge from the external ear canal. D—Photograph obtained during total ear canal ablation. Notice the mass in the external ear canal. E—Photograph of the resected portion of the ear canal. Notice the broad mass, which was identified as a trichoepithelioma. F—Photograph of the healed surgical site 4 weeks after total ear canal ablation and lateral bulla osteotomy.

    View larger version(72K) Figure 2— Transverse CT images of the head of the rabbit in Figure 1 obtained at the level of the tympanic cavities and right external ear canal before administration of contrast medium (A) displayed in a bone window (window width, 2,000 Hounsfield units; window length, 300 Hounsfield units) and after IV administration of contrast medium (B) displayed in a soft tissue window (window width, 400 Hounsfield units; window length, 40 Hounsfield units). In panel A, notice the incomplete osteolysis of the right tympanic bulla (arrow). In panel B, notice the irregularly polypoid, heterogeneously soft tissue and mineral attenuating, peripherally contrast-enhancing mass (asterisk) filling and extending laterally from the right external ear canal; similar material fills the right tympanic cavity.

    Five weeks after the initial evaluation, a total ear canal ablation and lateral bulla osteotomy were performed by use of described methods.2,3 The rabbit was premedicated with midazolam (1 mg/kg [0.45 mg/lb], SC) and oxymorphonek (0.18 mg/kg [0.08 mg/lb], SC). After anesthetic induction with isoflurane (administered with a face mask), the rabbit was intubated and anesthesia was maintained with isoflurane. Additional pain management treatments included a fentanyll constant rate infusion (15 μg/kg/h [6.82 μg/lb/h]; administered throughout the procedure) and buprenorphinem (30 μg/kg [13.64 μg/lb], IV; administered 30 minutes prior to the end of anesthesia and continued for 3 more doses, q 8 h). The tumor in the vertical portion of the external ear canal did not penetrate the osseous bulla (Figure 1). Moderate blood loss (estimated 2% of body weight) occurred during debridement of bone fragments from the bulla. Following lateral bulla osteotomy, amikacin-impregnated plaster of Paris antimicrobial beadsn and ceftiofurimpregnated polymethyl methacrylate beadsn were placed in the remaining portion of the tympanic bulla. The deep portion of the subcutaneous tissue was closed in a simple interrupted pattern,o and the remaining subcutaneous tissue was closed in a simple continuous pattern.o The skin was closed in a simple continuous pattern.p After surgery, the patient received fresh whole blood (25 mL administered over 3 hours; 9 parts blood to 1 part acid-citrate-dextrose solutionq) that had been collected from a donor rabbit within 1 hour prior to administration. The patient recovered from anesthesia without complications. Home care instructions were routine and included monitoring of the surgical site to detect complications and monitoring of appetite and fecal production. Administration of meloxicam (0.3 mg/kg, PO, q 24 h for 5 doses) and procaine penicillin G benzathine (50,000 U/kg [22,727 U/lb], SC, q 5 d for 2 doses) was continued. Further, a petroleum-based lubricantr was applied to the right eye every 4 hours for 2 weeks because of temporary right facial nerve paresis that developed secondary to the total ear canal ablation and lateral bulla osteotomy.

    Aerobic and anaerobic bacterial culture results for samples collected from the right tympanic bulla indicated no growth. Histologic examination of the surgical biopsy sample, which consisted of the resected mass in the vertical portion of the right ear canal and bone fragments from the tympanic bulla, indicated a well-demarcated unencapsulated lobular exophytic mass (Figure 2) expanding the dermis and invading to but not breaching the aural cartilage (Figure 3). The histologic diagnosis was malignant trichoepithelioma (matrical carcinoma) with squamous differentiation and intralymphatic invasion. The endoscopic biopsy sample that had been obtained before surgery was reexamined; results were consistent with the initial results (benign trichoepithelioma). The surgical biopsy sample contained similar benign areas superficially with irregular and malignant-appearing areas deep in the tissue that were not represented in the sample obtained before surgery. Histologic examination of the tympanic bulla bone fragment indicated osseous metaplasia and osteomyelitis with intralesional bacteria.

    View larger version(115K) Figure 3— Photomicrographs of a trichoepithelioma in the external ear canal of the rabbit in Figure 1. A—Photomicrograph of an endoscopic biopsy sample indicating a benign histologic appearance. H&E stain; bar = 200 μm. B—Photomicrograph of a surgical biopsy sample indicating a malignant histologic appearance. H&E stain; bar = 200 μm. C—Photomicrograph of a surgical biopsy sample indicating lymphatic invasion of the malignant trichoepithelioma. H&E stain; bar = 100 μm.

    The surgical site healed without complications, although the rabbit had mild facial asymmetry and signs of facial nerve damage for several days following surgery. Because the tumor was malignant and had not been completely removed, adjuvant radiation therapy and systemic administration of chemotherapeutic drugs were offered; these treatments were declined by the owner.

    The rabbit was reevaluated 22 weeks after surgical treatment. Results of physical examination were unremarkable except for a movable subcutaneous mass (approx 3 × 3 × 2 cm) in the area just caudal to the right mandibular ramus. The surgical site had healed completely. Repeated pre- and postcontrast CT of the head and neck was performed after the rabbit was sedated (midazolam [0.5 mg/kg] and butorphanol [0.25 mg/kg], IM). Transverse plane CT images were obtained before and after IV administration of iodinated contrast mediumc (2.2 mL of iohexol/kg; 300 mg of iodine/mL). Results of CT indicated a large soft tissue mass in the right retromandibular region, static lysis of the right temporal bone, and new lysis of the bones of the right inner ear. Findings of cytologic examination of a fine-needle aspirate of the mass were consistent with an epithelial carcinoma with squamous differentiation. In addition, there was abundant necrotic cellular material and moderate inflammation characterized by a mixed population of heterophils and macrophages. Given the history of malignant trichoepithelioma, tumor recurrence was suspected. Results of aerobic bacterial culture of the mass indicated no growth. Treatment options discussed with the owners at that time included marginal surgical reexcision of the tumor and local lymph node, followed by palliative or curative-intent radiation therapy, chemotherapy, and treatment with a cyclooxygenase-2 inhibitor. The owner decided to treat the rabbit only with meloxicam (0.3 mg/kg, PO, q 12 h).

    Thirty-three weeks after total ear canal ablation and lateral bulla osteotomy and 38 weeks after the initial evaluation, the rabbit was reevaluated because of increasing size of the right retromandibular region tumor and increased local self-excoriation. The rabbit's appetite and body weight remained stable, but it had increasing difficulty drinking from a water bottle. Physical examination revealed the right mandibular mass had substantially enlarged and was fluctuant. Removal of a superficial crust resulted in discharge of hemorrhagic, malodorous fluid. The skin over the mass was partially discolored and necrotic. On the basis of a poor prognosis, the animal was euthanized and a complete necropsy performed. Multiple masses and enlarged lymph nodes (often with central necrosis) were identified in the region caudal to the right mandibular ramus and surgical site. Histologic findings confirmed a recurrent and metastatic malignant trichoepithelioma with rafts and islands of neoplastic epithelial cells in connective tissue, many lymphatics, and, rarely, small blood vessels in the region of the previously removed right ear canal and bulla. The local draining lymph nodes were almost completely effaced by large amounts of necrosis, with few islands of viable neoplastic cells.