Definitive Radiotherapy as a Treatment for Presumed Brainstem Meningioma Causing Collet-Sicard Syndrome in Dogs: A Case Series.

Collet-Sicard syndrome (CSS) is a rare neurological condition characterized by concomitant dysfunction of cranial nerves (CNs) IX-XII, resulting in variable combinations of dysphagia, dysphonia, and tongue paresis or paralysis. This retrospective case series describes three dogs diagnosed with CSS secondary to a suspected brainstem meningioma that were treated with definitive radiotherapy (RT). All dogs received volumetric-modulated arc therapy with a total dose of 50 Gy (20 × 2.5 Gy fractions). Supportive medical management was maintained during and after RT. Clinical signs varied among dogs depending on the severity of CN involvement, and all showed clinical improvement after RT. Two dogs who achieved stable disease post-RT were euthanized due to progressive clinical signs at 344 and 421 days post-RT, while one dog who achieved partial response post-RT remains alive with sustained clinical improvement at 652 days. No early or late adverse effects were recorded. This case series describes the use of RT, follow-up advanced imaging, and medical management for the treatment of CSS in three dogs with suspected neoplastic causes.