Can definitive radiotherapy meaningfully improve outcomes in dogs with Collet–Sicard syndrome?

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

Silvia Caeiro, Juan Carlos Serra, Megan Madden, Magdalena Parys

Background

Collet–Sicard syndrome (CSS) is a rare cranial neuropathy caused by lesions affecting the jugular foramen and hypoglossal canal, resulting in dysfunction of cranial nerves IX–XII. In dogs, CSS has not been previously well described, and treatment options and prognosis are poorly defined. Intracranial meningiomas are the most common primary brain tumors in dogs, and radiotherapy (RT) is an established treatment for presumptive meningioma; however, outcomes in dogs with CSS secondary to presumed meningioma are unknown. The aim of this study was to describe clinical outcomes in dogs with CSS caused by suspected brainstem meningioma treated with definitive-intent RT.

Methods

This retrospective case series included three dogs diagnosed with CSS based on neurological examination and MRI findings consistent with extra-axial masses involving the cerebellopontine angle, jugular foramen, and hypoglossal canal. All dogs underwent definitive-intent volumetric-modulated arc therapy (VMAT), receiving a total dose of 50 Gy delivered in 20 daily fractions of 2.5 Gy. CT and MRI were used for treatment planning and follow-up when available. Medical records were reviewed for signalment, clinical signs, imaging findings, RT protocol details, supportive medical management, adverse events, tumor response, and survival.

Results

All dogs showed clinical improvement following RT, particularly in signs related to lower cranial nerve dysfunction such as gagging, retching, coughing, and dysphagia. Follow-up imaging demonstrated either partial response or stable disease in all cases. One dog achieved a partial response with sustained clinical improvement and remained alive 652 days post-RT at last follow-up. Two dogs achieved stable disease but were euthanized at 344 and 421 days post-RT due to progressive neurological signs. No acute or late radiotherapy-associated toxicities were reported.

Limitations

The study was limited by its small sample size and retrospective design. Diagnosis of meningioma was presumptive, based on imaging findings without histopathologic confirmation. Follow-up imaging was not available at the time of euthanasia for two dogs, preventing confirmation of disease progression. These factors limit generalization of outcomes and definitive conclusions regarding tumor control.

Conclusions

Definitive-intent radiotherapy was associated with meaningful clinical improvement and prolonged survival in dogs with CSS secondary to presumed brainstem meningioma. Outcomes appeared superior to those previously reported with medical management alone. This case series supports RT as a viable treatment option for dogs with neoplastic CSS, although further studies are needed to better define prognosis and optimize treatment protocols.

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