Occipito‐atlanto‐axial ganglion cyst in a medium‐sized mixed‐breed dog

Abstract A 10‐year‐old, spayed female mixed‐breed dog (26.7 kg bodyweight) was presented with progressively worsening cervical pain over the course of 1 week. Neurological examination was unremarkable, except for a mild left‐sided Horner's syndrome. Magnetic resonance imaging (MRI) revealed markedly dilated atlanto‐occipital and atlanto‐axial joint capsules bilaterally, causing predominantly dorsolateral compression of the spinal cord at the level of the C1 vertebral body. Surgical partial excision of the ventral capsules of the occipito‐atlanto and atlanto‐axial joints via a ventral approach, with subsequent removal of the gelatinous contents, was performed. Postoperatively, pain resolved completely within 2 weeks. Histopathological analysis confirmed the diagnosis of a ganglion cyst. At the 1‐year follow‐up, the dog remained pain free, exhibiting only minor residual left‐sided Horner's syndrome. Follow‐up MRI demonstrated complete resolution of the spinal cord compression. This case highlights occipito‐atlanto‐axial intraspinal ganglion cysts as a rare differential diagnosis in dogs presenting with cervical myelopathy.