THO

Question 1

Clinical signs assoc with THO

Answer 1

Headshaking, ear rubbing/POP, quidding, and weight loss.

CN signs incl. facial paralysis with secondary corneal ulcers (facial nerve), vestibular syndrome with varying degrees of ataxia (vestibulocochlear nerve), and dysphagia and/or signs of oesophageal dysfunction (vagal nerve)

Acute exacerbation of CSs is seen with fracture of the petrous temporal or stylohyoid bones , incl worsening ataxia, CN deficits and even seizures and acute death

Question 2

Medical therapy for THO and reported outcomes by Espinosa 2017 (EVJ)?

Answer 2

Rest, anti-inflammatories (NSAID +/-dex), ABs, +/- vit E

Px fair-poor with medical management. Of 20 tx horses, 2 returned to full function (12.5%)

6 worsened, 5 had no improvement and 7 imporved slightly

Medical management significantly associated with non-survival

Question 3

List the surgical treatment options for THO

Answer 3

1. Partial stylohyoid ostectomy (PSHO)
2. Ceratohyoidectomy. This has been reported standing (Racine et al 2019 VS)

Complication rate higher for PSHO so ceratohyoidectomy is the tx of choice

Question 4

Label the parts; ventral view, cranial to the right

Answer 4

Blue - basihyoid bone w lingual process

Green - Ceratohyoid bone

Pink - Thyrohyoid bone

Question 5

List the steps in the surgical procedure for standing ceratohyoidectomy described by Racine et al (2019 VS)

Answer 5

1) 10cm skin incision from 2cm caudal to the basihyoid running rostrally, midway between midline and mandible (care re linguofacial vein)
2) Superficial muscle dissection: Sternohyoid and omohyoid muscles separated to expose basihyoid & its articulation with ceratohyoid. Mylohyoid muscle was separated from the deeper seated hyoglossus muscle.
3) Deeper muscle dissection: hyoglossus muscles separated bluntly separated. Must remain on medial aspect of ceratohyoid (hypoglossal and glossopharyngeal nerves and lingual artery are on lateral aspect)
4) Basihyoid/ceratohyoid articulation transected w Mayos, ceratohyoid bone was grasped with a pair of Backhaus towel clamps to allow rostral and ventral traction of the bone - NOT excessive traction.
5) The ceratohyoid muscle was digitally separated from the caudal aspect of the ceratohyoid bone.
6) Disarticulate ceratohyoid-stylohyoid junction w Mayos (care re haem from lingual aa)
7) Close front and back of incision, middle open for drainage

Question 6

Most likely and significant intra-op complication of ceratohyoidectomy (standing or GA)

Answer 6

Intra-operative haemorrhage.

Most at risk during disarticualtion of ceratohyoid stylohyoid articulation as the lingual artery runs axially toward the tongue at this point.

If not dealt with sufficiently, may cause URT obstruction necessitating tracheotomy. Wise to have blood donor on standby as haem can be significant

Question 7

Outcome reported by Racine et al (2019 VS) following standing ceratohyoidectomy for THO

Answer 7

All 4 cases had no PO complications, returned to previous use and there was excellent owner satisfaction

There was rapid (days) improvement of ataxia and a progressive improvement (over weeks to 6 months) of facial paralysis

Question 8

What was the presenting clinical signs subsequently dx dt THO in the case report by Grant and Barnett, EVE 2019

Answer 8

Ipsilateral shermouth

Corrected over 18mo following ceratohyoidectomy

No neuro or other signs at all