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mandible, centred within Viborg’s triangle (McCarthy 1990). On palpation, the mass was firm and extended in a rostral direction, medial to the mandible. It also extended across midline, dorsal to the larynx and could be palpated on the right side. Due to the gelding’s severe respiratory distress, a tracheotomy was performed without delay, approximately 20 cm caudal to the larynx. The horse’s respiratory distress resolved immediately upon placement of a tracheotomy tube.
After the tracheotomy was performed, the gelding had a
normal heart rate of 44 beats/min, respiratory rate of 20 breaths/min and temperature of 37.2°C (99.9°F). Jugular fill was within normal limits bilaterally when the vein was distended. Clear mucoid discharge was present in the right nostril. Except for the aforementioned left retropharyngeal mass and associated swelling, all other physical examination parameters were within normal limits. Packed cell volume was normal at 37%, as was the total solids concentration at 7.2 g/dL (reference range, 6.0–8.5 g/dL). Complete blood count and chemistry were fairly unremarkable, with a very mild neutrophilia (6.1 9 109 neutrophils/L; reference range, 3.0–6.0 9 109 neutrophils/L) as the only abnormal finding. Total white blood cell count and morphology (8.3 9 109 WBC/L; reference range, 6.0–12.0 9 109 WBC/L), lymphocytes (1.6 9 109 lymphocytes/L; reference range, 1.5–5.0 9 109 lymphocytes/L) and fibrinogen (3.0 g/L; reference range, 1.0– 4.0 g/L) were within normal limits.
Endoscopy Upper airway endoscopy revealed normal anatomy from the nostrils to the dorsal pharyngeal recess. Extending caudally from the dorsal pharyngeal recess, the dorsal pharyngeal wall coursed ventrally (complete ventral collapse), obscuring any view of the larynx. Once the endoscope was advanced beyond the ventral pharyngeal collapse, the caudal left and right pharyngeal walls were severely collapsed axially,
creating a very small airway to the larynx. The arytenoids were observable through a small opening in the compressed and inflamed pharynx. The arytenoids appeared to have a small amount of movement, but due to the amount of compression and swelling, there was very little room for them to abduct. White, foamy mucus was present in the caudal pharynx and entering the trachea. A small amount of blood, likely from the tracheotomy procedure, and a moderate amount of mucus were present in the trachea. Both guttural pouches were within normal limits.
Ultrasonography Ultrasonography of the mass and surrounding region was performed. The mass was multilobular with a diffusely heterogeneous echogenicity and indistinct margins. It enveloped the left common carotid artery without occluding it. The adjacent tissues were oedematous.
Aspirate and biopsy Needle aspiration of the mass was performed to rule out an abscess and collect a sample for cytology, which revealed cellular samples that contained a predominance of intermediate to large, atypical lymphoid cells, with few small, mature lymphocytes, suggestive of lymphoma (Fig 2). A tissue biopsy was obtained from the ventral aspect of the mass. The horse was maintained on trimethoprim-sulfamethoxazole1 (25 mg/kg bwt per os q. 12 h) and flunixin meglumine2 (1.1 mg/kg bwt per os q. 12 h; Prevail) while awaiting results. Histopathology demonstrated dense sheets of pleomorphic
round cells interspersed by large confluent regions of necrosis (representing about 25% of the sample). The background stroma was fine and contained many small tortuous vessels. Some small mature lymphocytes were present (Fig 3). Neoplastic cells were large (often 39 the size of a red blood
cell or larger). There were up to 50 mitoses in 10 high-power fields. These preliminary histopathological findings supported the cytological diagnosis of a round cell tumour, likely lymphoma.
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20 um
Fig 1: A large, firm soft tissue mass (arrows), externally appreciable as approximately 12 3 12 cm (craniocaudal by dorsoventral), is present in the left retropharyngeal region. Image taken after the placement of a tracheotomy tube.
© 2017 EVJ Ltd
Fig 2: Cytological findings of a malignant round cell neoplasm, interpreted as lymphoma, from a needle aspirate of a mass in the retropharyngeal region of a horse. Large atypical lymphoid cells (asterisks) predominate, with few small, mature lymphocytes (arrow heads) and erythrocytes scattered throughout. (Wright’s stain; 203 objective; bar = 20 lm).
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