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EQUINE VETERINARY EDUCATION
Equine vet. Educ. (2018) 30 (2) 64-69 doi: 10.1111/eve.12607
Case Report
Guttural pouch leiomyosarcoma causing nasopharyngeal compression in a pony
S. J. Drew†*, L. Meehan‡, R. J. M. Reardon‡, B. C. McGorum‡, P. M. Dixon‡ and J. Del-Pozo† †Easter Bush Pathology; and ‡Equine Hospital, Royal (Dick) School of Veterinary Studies and Roslin Institute, The University of Edinburgh, Roslin, Midlothian, UK. *Corresponding author email:
Stephen.Drew@ed.ac.uk
Keywords: horse; guttural pouch; nasopharyngeal compression; computed tomography; leiomyosarcoma
Summary A 14-year-old Connemara cross gelding presented with abnormal respiratory noise and exercise intolerance. Upper airway endoscopy, ultrasonography, radiography and computed tomography revealed a large mass within the left guttural pouch causing marked left dorsal nasopharyngeal collapse and displacement and compression of the right guttural pouch. The horse was subjected to euthanasia and a post-mortem examination confirmed the above findings. Histological and immunohistochemical examinations of the mass confirmed a diagnosis of guttural pouch leiomyosarcoma, a lesion previously unreported at this site.
Introduction
Abnormal respiratory noise and exercise intolerance is a relatively common clinical presentation in the horse and can be associated with structural, functional, inflammatory, infectious and neoplastic disorders of the nasal passages, sinuses, hard and soft palate, larynx and nasopharynx. The close anatomical proximity between the ventral floor of the guttural pouches and the dorsal nasopharyngeal roof means that guttural pouch distension can cause dorsal nasopharyngeal compression and is a differential diagnosis in such cases. Neoplasia of the guttural pouch is rare (Hance and Bertone 1993; Baptiste et al. 1996; Caswell and Williams 2007; Freeman 2015). This report describes the clinical, ancillary diagnostic and pathological findings in a case of primary guttural pouch leiomyosarcoma, a lesion that does not appear to have been previously described in horses.
Case history and clinical findings
A 14-year-old Connemara cross gelding, used for pleasure and low level competition, was presented for abnormal, harsh respiratory noise during ridden work and exercise intolerance which had become progressively worse over the preceding 2 weeks. It was reported that the horse had demonstrated episodes of coughing 4 months previously, which had improved with medical management and had been attributed to lower airway disease. On presentation, the gelding was bright and alert, with mild swelling of the parotid region bilaterally and a mild bilateral (but predominantly left sided) seromucoid nasal discharge. The submandibular lymph nodes were not enlarged. No abnormal respiratory noise was audible at rest, but inspiratory stridor was appreciated during light in-hand exercise.
© 2016 EVJ Ltd Investigation
In view of the above presenting signs, the horse was isolated pending further investigation of potential infectious causes, particularly Streptococcus equi subsp. equi infection. Upper airway endoscopy revealed marked dorsal nasopharyngeal collapse, greater on the left side, with marked reduction in the diameter of the nasopharynx rostral to, and overlying, the rima glottidis. Mucoid discharge was seen to emanate from the left guttural pouch ostium, accumulating on the floor of the nasopharynx. Endoscopy of the right guttural pouch revealed marked compression of its medial compartment. A guttural pouch lavage was negative for Streptococcus equi subsp. equi on both culture and qPCR. Endoscopic access to the left guttural pouch was difficult as the ostium was collapsed and displaced medioventrally. Once access was gained, it showed loss of the normal air filled guttural pouch lumen that was replaced by a wall of soft tissue which prevented further endoscopic evaluation.
Diagnostic imaging
A laterolateral radiograph of the pharyngeal region (Fig 1a) identified a large, well defined, soft tissue opacity within the region of the guttural pouches, which extended caudally to the midpoint of C2 and ventrally to a level 1 cm dorsal to the soft palate that was causing marked dorsal nasopharyngeal compression. There was a narrow margin of gas dorsal to the mass, believed to be air within the guttural pouches. Transcutaneous ultrasonography of the left parotid region caudal to the left temporomandibular joint revealed an ovoid, soft tissue mass approximately 3 cm below the skin surface (Fig 1b). This mass was of soft tissue echogenicity, well encapsulated and contained multiple, small, ovoid, hypoechoic regions resulting in a heterogeneous honeycomb appearance.
Surgical biopsy
The horse was sedated (detomidine [Medesedan]1 0.01 mg/ kg bwt i.v. and butorphanol [Butador]2 0.02 mg/kg bwt i.v.) and local anaesthesia administered (lignocaine hydrochloride 2% and epinephrine acid tartrate 0.00198% [Lignol]3 30 ml). A modified Whitehouse approach was made to gain access to the left guttural pouch. Following incision into the pouch the base of a rounded, firm, soft tissue mass in the lateral compartment was palpable. An excisional biopsy was taken from the directly visualised ventral aspect of this
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