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EQUINE VETERINARY EDUCATION
Equine vet. Educ. (2022) 34 (2) 96-102 doi: 10.1111/eve.13508
Image Article
Use of serial standing computed tomography for diagnosis, treatment and monitoring of a horse with acute myonecrosis of the head
S. Boorman* , S. Zetterstr€ and F. Caldwell
om, J. Hamersky, A. Velloso Alvarez , L. Boone , R. R. Hanson
Department of Clinical Sciences, College of Veterinary Medicine, Auburn University, Auburn, Alabama, USA *Corresponding author email:
szb0163@auburn.edu Keywords: horse; computed tomography; myonecrosis; myositis; Prevotella intermedia; Peptostreptococcus asaccharolyticus
Summary An 11-year-old American Quarter Horse gelding was referred to the JT Vaughan Large Animal Teaching Hospital at Auburn University, College of Veterinary Medicine, for investigation of acute and severe right-sided facial swelling and nasal discharge. Standing computed tomographic (CT) examination of the head identified severe soft tissue swelling surrounding the right mandible, emphysema within the soft tissues tracking along fascial planes and right-sided caudal and rostral maxillary sinusitis. Using CT identification and ultrasound guidance, several targeted fasciotomies were created into the right masseter, cranial cervical musculature, supraorbital space and caudo-medial aspect of the mandible. The right-sided sinusitis was treated by right conchofrontal sinus trephination and lavage. Aerobic and anaerobic cultures obtained from the fasciotomy sites and conchofrontal sinus both yielded Prevotella intermedia and Peptostreptococcus asaccharolyticus. During hospitalisation, serial, standing CT examinations were performed for monitoring case progression and guiding further fasciotomies in the face of continued myonecrosis. Follow-up CT performed at 1 month showed resolution of the emphysema and presence of chronic right ventral conchal sinusitis. The sinusitis was treated by fenestration of the right ventral concha with a diode laser via the nasal passage.
Introduction
Severe, acute subcutaneous emphysema progressing to oedema and necrosis of the soft tissues following breach of the epithelium by anaerobic bacteria, usually a Clostridium species, is a relatively rare but potentially life-threatening phenomenon. A 2003 review of 37 cases of clostridial myonecrosis determined that the majority of instances occurred following an intramuscular injection, with a small number occurring in association with a wound (Peek et al. 2003). The resultant myonecrosis surrounded the respective injection site, commonly the cervical or gluteal musculature. These anatomical areas contain relatively few large neurovascular structures, allowing the treating clinician to perform fasciotomies to aerate the offending bacteria and drain the accumulated purulent material without the need for meticulous surgical planning. The following case report describes the use of serial, standing computed tomography (CT) examinations to guide diagnosis, fasciotomies and treatment monitoring of severe, acute myonecrosis of the
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head. Serial CT examinations allowed for the precise planning for multiple fasciotomies in a region where the surgical anatomy is daunting in both complexity and importance.
Case history
An 11-year-old American Quarter Horse gelding was referred to Auburn University JT Vaughan Large Teaching Hospital for investigation of acute and severe right-sided facial swelling and malodorous nasal discharge. One day prior to presentation, the patient presented to the referring veterinarian with depressed mentation, right-sided facial swelling and a fever of 40°C. A complete blood count revealed lymphopenia
(340 cells/uL) and
hyperfibrinogenaemia (5.1 g/L). Skull radiographs identified rounding of tooth root 108 and fluid opacity within the right side of the rostral and caudal maxillary sinuses. An oral
examination was unremarkable. Despite treatment with flunixin meglumine (1.1 mg/kg bwt i.v.), phenylbutazone (2.2 mg/kg bwt i.v.), dexamethasone (0.01 mg/kg, bwt i.v.), dimethyl sulphoxide (0.1 g/kg bwt i.v.), dipyrone (30 mg/kg bwt i.v.) intravenous fluid therapy and enrofloxacin (7.5 mg/ kg bwt i.v.), there was progression of the facial swelling and loss of airflow of the right nostril.
Clinical findings
At presentation, the gelding was bright, alert and responsive. The rectal temperature was elevated at 39.1°C, the heart rate was elevated at 56 beats/min and the respiratory rate was slightly increased at 24 breaths/min. The horse’s mucous membranes were pink and moist with a normal capillary refill time of less than 2 s. The right side of the face was profoundly swollen, including the right peri- and retro-orbital space with resultant exophthalmos and chemosis. The swelling extended from the level of the throat latch rostrally to the right nostril, including the soft tissues overlying the vertical and horizontal rami of the right mandible (Fig 1). Airflow was not appreciated through the right nostril. Abundant malodorous, mucopurulent right-sided nasal discharge was noted. The left nostril had appropriate airflow and was free from discharge. The mandibular lymph nodes were bilaterally enlarged. Absence of the right palpebral reflex was detected on cranial nerve examination but was considered to be due to severe head swelling and not due to cranial nerve deficit
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