EQUINE VETERINARY EDUCATION / AE / FEBRUARY 2022
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LightSpeed VCT CT System, 160 mA, 120kV)3, and images were reconstructed in both bone and soft tissue algorithms at a slice thickness of 5.0 mm. Severe soft tissue swelling contouring the right mandible abaxially from the first premolar to the atlas was identified, extending across the entire abaxial aspect of the right maxillary bone. Numerous coalescing gas bubbles were present throughout the soft tissue swelling and were noted tracking along multiple fascial planes (Fig 2). The swelling along the axial aspect of the right vertical mandible caused mild axial compression of the nasopharynx and axial deviation of the guttural pouch. This swelling extended into the right caudal periorbital space, where pinpoint areas of gas within the right orbital fissure were observed. A mild, focal area of irregular periosteal response was noted along the medial contour of the right horizontal mandible. Fluid and soft tissue attenuating material was present within the right rostral and caudal maxillary sinus, the right sphenopalatine sinus, right dorsal and ventral conchal bulla. Infundibular gas and rounding of the apical roots were noted in teeth 109 and 110. No foreign body or evidence of a penetrating wound could be identified.
Fig 1: Side photograph of an 11-year-old American Quarter Horse gelding at presentation for treatment of acute and severe right-sided facial swelling and nasal discharge. Note the severe swelling of the right periorbital space, eyelids, across the lateral surface of the ventral head and labial commissure. Foetid right- sided nasal discharge was present.
because other reflexes associated with the facial nerve were intact.
Initial investigation and treatment
Initial diagnostics included complete blood count, serum biochemistry, transcutaneous ultrasonographic examination of the thorax and abdomen (Aplio i700 TUS-AI700; Canon)1, upper airway endoscopy and ophthalmological examination of the right eye. A mild lymphopenia, moderate thrombocytopenia and moderate hypomagnesaemia were identified (1100 lymphocytes/µl, 6700 platelets/µl and 0.45 mmol/L magnesium, respectively). Mild comet-tail artefacts along the right cranioventral lung field were identified by thoracic ultrasonography, consistent with mild pleural roughening. The remainder of the ultrasonographic examination was unremarkable. Upper airway endoscopy identified thick purulent discharge at the right nasomaxillary aperture. No other abnormalities of the guttural pouches, pharynx or the proximal trachea were identified. Ophthalmological examination confirmed exophthalmos and chemosis of the right side, but no other abnormalities of either eye were detected. Sedated oral examination using a dental camera2 did not identify any foreign body or penetrating wound in the oral mucosa. Chronic buccal ulceration associated with sharp points was noted on the left side. Infundibular caries of teeth 109 and 110 were noted. No teeth were loose or fractured.
Advanced imaging
A standing sedated CT examination of the head and cervical region was performed using a 16-slice CT scanner (GE
Surgical treatment
Based on the CT, a diagnosis of myonecrosis of the right side of the head with right-sided secondary sinusitis was made, though whether dental disease or other penetrating injury was implicated could not be determined. The anatomical regions on CT containing the greatest emphysema were selected as fasciotomy sites. Fasciotomies were performed under standing sedation and local anaesthesia; one into the supraorbital adipose tissue, three across the lateral aspect of the mandible (i.e. into the masseter, ventral to the approximated location of the facial nerve) and one at the caudo-medial aspect of the horizontal ramus of the mandible. Ultrasonographic guidance was used to guide the fasciotomy at the medial aspect of the mandible to avoid penetration of the facial artery or linguofacial vein. Purulent discharge along with necrotic muscle and adipose tissue was obtained from the fasciotomy sites and a sample submitted for aerobic and anaerobic culture. The sites were lavaged with sterile polyionic solution. A Penrose drain was placed connecting the rostral and caudal lateral masseter incisions and secured in place. The right conchofrontal sinus was opened with a ¾” Horsley’s trephine and a sample of the purulent discharge within the sinus was submitted for culture (separate from the fasciotomy culture). The sinus was lavaged and a 20 French Foley catheter left in situ for serial lavage.
Case progression and post-operative treatment
Treatment was initiated with potassium penicillin (44,000 iu/kg bwt q. 6 h, i.v.), metronidazole (15 mg/kg bwt q. 8 h, per os) and flunixin meglumine (1.1 mg/kg bwt q. 12 h, i.v.). Initially, the gelding had persistent tachycardia (60 beats/min) and additional pain relief was provided (morphine, 0.1 mg/kg bwt
q. 8 h, i.v.). The gelding had a recurring fever responsive to flunixin meglumine administration. Fasciotomy sites were lavaged twice daily with a dilute betadine solution. The sinus was flushed once a day with a balanced ionic solution until resolution of the purulent sinus material and removal of the Foley catheter (3 days). Repeat bloodwork performed at 48 h
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