A 14-month-old male neutered Dobermann presented for investigations into lingual paresis, dysphagia and proprioceptive ataxia of the pelvic limbs. Magnetic resonance imaging (MRI) revealed a mass lesion in the brainstem. Treatment with glucocorticoids and radiation therapy (RT) achieved a good quality of life for 6 months, after which deterioration occurred. Repeated MRI revealed an expansion of the mass lesion, after which the owners elected for the patient to be euthanised. Postmortem histological examination and immunohistochemistry confirmed the presence of a gemistocytic astrocytoma. This case report describes the first case in the veterinary literature of a young dog with a brainstem gemistocytic astrocytoma treated with RT and glucocorticoids, with remission of clinical signs and excellent quality of life for 6 months after treatment.

A 16-month-old, female entire, Thai Ridgeback was presented for evaluation of a two subcutaneous, non-painful, fluctuant masses associated with two firm tubular tracts in the soft tissue dorsal to the sacrum and proximal caudal vertebrae originating at the skin surface slightly to the right of the tail base. Physical and neurological examination was otherwise normal. Magnetic resonance imaging of the lumbosacral spine revealed two dermoid sinuses type I and type II. Surgical resection and histopathological examination confirmed the presumed diagnosis. To the authors' knowledge, the presence of two dermoid sinuses in this location has not been previously described in a Thai Ridgeback or in another dog breed in the veterinary literature. The prognosis following surgical resection appears favourable. BACKGROUNDA dermoid sinus (DS) is an embryonic/congenital development defect that results in an incomplete separation between the skin and the ectodermal neural tube. 1 A sinus tract is lined with squamous epithelium, hair follicles and sebaceous glands, with a small cutaneous opening on the dorsal midline that extends ventrally from the skin to the subarachnoid space or dura mater or ends as a blind sac at a different depth. 2,3 DSs are classified based on the degree of ventral extension (I-VI) (Figure 1). DSs are more often located in the cervical and craniothoracic regions but can also occur anywhere along the spine and even in the head. 1,[4][5][6][7][8][9][10] This disorder is encountered most commonly in Rhodesian Ridgeback dogs, but has been reported in other breeds such as Dachshund, 11 Great Pyrenees dog, 12