Diagnostic Imaging of Diseases Affecting the Guttural Pouch

The most common diseases of the guttural pouch are empyema, tympany, mycosis and temporohyoid osteoarthropathy. The challenge in diagnosis of guttural pouch diseases lies in the complex anatomy of the guttural pouch and adjacent associated structures. Diagnostic imaging is a good complement to endoscopy for the diagnosis of some guttural pouch diseases, especially to make a full assessment of the lesions involving the pouch and surrounding structures. This review article describes the value of each diagnostic imaging technique in the diagnosis of guttural pouch disease and the corresponding imaging findings. Radiography is generally used as the first line to complement endoscopic findings, and can give useful additional information although it is limited by superimposition. Ultrasonographic examination of the guttural pouch is of limited value due to the presence of gas in the guttural pouch but can eventually be used to detect fluid within the pouch or can help to evaluate the soft tissues located lateral and ventral to the guttural pouch. Cross-sectional imaging, especially CT, is increasingly available and appears to be the best technique to fully assess the surrounding soft tissues and to precisely identify lesions of the temporohyoid apparatus, temporal bone and skull base that are associated with guttural pouch disease.

Partial ceratohyoidectomy as surgical treatment for horses with temporohyoid osteoarthropathy: 10 cases (2010-2021)

OBJECTIVE

To describe outcomes of horses with temporohyoid osteoarthropathy (THO) treated with partial ceratohyoidectomy.

ANIMALS

10 client-owned horses.

PROCEDURES

Medical records from 2 institutions were examined for records of horses with THO treated with partial ceratohyoidectomy between 2010 and 2021. History, signalment, clinical signs, diagnostics, medications, and surgery-related details were recorded. Horses with a minimum of 6 months follow-up were recruited for neurologic and imaging examinations in the hospital or field where radiography of the basihyoid-ceratohyoid articulation were performed along with CT, when available.

RESULTS

10 horses with THO were included (9 unilateral; 1 bilateral). Nine planned partial ceratohyoidectomies were performed in 8 horses, whereas 2 horses had preoperatively planned complete ceratohyoidectomies transitioned to partial ceratohyoidectomies during surgery due to intraoperative complications. Postoperative complications occurred mostly in transitioned surgeries (obstructed airway, tongue mobility issues, and incisional hemorrhage), whereas only 1 horse with a planned ceratohyoidectomy had postoperative complication of rhabdomyolysis. All complications resolved before hospital discharge. Neurologic signs improved in all 10 horses, with 2 showing complete resolution. Nine horses were available for radiographic follow-up, 6 of which also had head CT scans. A space between the ceratohyoid and basihyoid bones was measurable on radiography in all 9 horses, and was confirmed on CT. Three horses demonstrated proliferation of either ceratohyoid or basihyoid bones. The 9 horses with unilateral disease returned to previous work, and the horse with bilateral disease was retired.

CLINICAL RELEVANCE

Partial ceratohyoidectomy is a surgical option for treatment of THO that provides similar clinical outcomes to published reports on ceratohyoidectomy.

Associations between styloid process sheath CT sizes and age, body weight, and breed in horses

The styloid process sheath (SPS) is a part of the tympanic temporal bone and an incomplete bony sleeve surrounding the styloid process, tympanohyoid cartilage, and dorsal part of the stylohyoid bone. In horses undergoing head CT, we observed a range of SPS sizes and questioned whether differences were early features of temporohyoid osteoarthropathy (THO) or normal anatomic variations associated with age, body weight, sex, or breed. We hypothesized that SPS sizes were positively correlated with age and body weight, but not with sex or breed. Using a convenience population of horses that underwent head CT at our institution (2008-2017), regardless of THO status, we investigated these hypotheses in a retrospective cross-sectional study. The sample comprised 102 horses. The median SPS height was larger medially (4.3 mm) than laterally (2.4 mm) and the median width was 11.1 mm: no difference was detected between sides. Geldings had a significantly larger median SPS width (11.6 mm) than stallions (8.7 mm; P < 0.05) and mares (10.0 mm; P < 0.05). No association was detected between SPS sizes and body weight and breed. Univariate and multivariate analyses initially found significant associations between SPS heights and age. Secondary analyses performed following removal of outliers and horses <2-years old found similar but less pronounced results (annual increase in SPS heights decreased from 3.2-3.8% to 0.9-2.6%). Most associations were insignificant when investigated by age group, but the annual rate of increased size might be faster in older horses. Excessive SPS enlargement was theorized as an essential component of THO.

Postmortem diagnoses of spinal ataxia in 316 horses in California

OBJECTIVE

To determine period prevalences of postmortem diagnoses for spinal cord or vertebral column lesions as underlying causes of ataxia (spinal ataxia) in horses.

ANIMALS

2,861 client-owned horses (316 with ataxia [ataxic group] and 2,545 without ataxia [control group]).

PROCEDURES

The medical records database of the University of California-Davis Veterinary Medical Teaching Hospital was searched to identify horses necropsied between January 1, 2005, and December 31, 2017. Results were compared between the ataxic and control groups and between various groups of horses in the ataxic group. Period prevalences were determined for the most common causes of ataxia.

RESULTS

2,861 horses underwent full necropsy, and the period prevalences for the most common definitive diagnoses for ataxia were 2.7% (77/2,861) for cervical vertebral compressive myelopathy (CVCM), 1.3% (38/2,861) for equine neuroaxonal dystrophy or equine degenerative myeloencephalopathy (eNAD-EDM), and 0.9% (25/2,861) for trauma; the period prevalence of ataxia of unknown origin was 2.0% (56/2,861). Horses in the ataxic group (vs the control group) were more likely to have been warmblood horses (OR, 2.70) and less likely to have been Arabian horses (OR, 0.53). In the ataxic group, horses < 5 (vs ≥ 5) years of age had greater odds of CVCM (OR, 2.82) or eNAD-EDM (OR, 6.17) versus trauma or ataxia of unknown origin. Horses in the ataxic group with CVCM were more likely Thoroughbreds (OR, 2.54), whereas horses with eNAD-EDM were more likely American Quarter Horses (OR, 2.95) and less likely Thoroughbreds (OR, 0.11).

CONCLUSIONS AND CLINICAL RELEVANCE

Results indicated that breed distributions differed for horses with CVCM versus eNAD-EDM; therefore, breed should be considered in the clinical evaluation of spinal ataxia in horses.

Ceratohyoidectomy in standing sedated horses

OBJECTIVE

To investigate the feasibility and complications associated with ceratohyoidectomy (CHE) in standing sedated horses unaffected (experimental horses) and standing sedated horses affected (clinical cases) with temporohyoid osteoarthropathy (THO).

STUDY DESIGN

Case series.

ANIMALS

Six experimental horses and four clinical cases.

METHODS

Standing CHE was performed in six experimental horses euthanized 30 minutes (n = 3) and 7 days (n = 3) postoperatively. The four clinical cases were presented because of central facial nerve paralysis (n = 3), vestibular ataxia (n = 3), auricular hemorrhage (n = 2), quidding (n = 1), and oesophageal impaction (n = 1). Evolution was assessed by clinical examination during hospitalization and later by telephone interviews for the clinical cases.

RESULTS

The procedure was successfully performed in all horses. Experimental horses did not show any short-term postoperative complications. Hemorrhage was experienced intraoperatively in one of the clinical cases and was successfully managed with placement of hemostatic forceps. Vestibular ataxia and other symptoms of THO improved within days, but facial nerve paralysis did not improve until 9 days to 6 months after surgery. Follow-up ranged from 9 to 24 months. All clinical cases returned to performance, and client satisfaction was excellent.

CONCLUSION

Ceratohyoidectomy was consistently feasible in standing sedated horses. The method did not result in postoperative complications and led to resolution of clinical signs associated with THO.

CLINICAL SIGNIFICANCE

Standing CHE should be considered in horses affected with THO, especially when horses present with marked vestibular deficits and ataxia, to reduce risks associated with recovery from general anesthesia.

Update on disorders and treatment of the guttural pouch

The most common disorders of the equine guttural pouches are empyema, tympany, mycosis, and temporohyoid osteoarthropathy. Diagnosis of these conditions is made primarily by imaging with endoscopy, radiographs, computed tomography, and/or MRI. Medical treatment with anti-inflammatories, antimicrobials, and/or antifungals may be successful in some cases, but many of these disorders necessitate surgical intervention. Direct surgical approaches to the guttural pouch are difficult because of their complex anatomy and relationship with important structures, thus precipitating a move toward minimally invasive procedures when possible.