Occipital Bone Angiomatosis and Chronic Subdural Hematoma Causing Severe Cerebellar and Brainstem Compression and Obstructive Hydrocephalus in a Young Adult Cat

A 2-year-old cat was presented for a 1-month history of cautious ambulation, head shaking, and lethargy, with severe spinal pain on neurologic examination. MRI and CT demonstrated marked endophytic thickening of the occipital bone diploe with widened intertrabecular spaces, irregular internal cortical margins, relative preservation of the outer cortex, and strong internal and perilesional contrast enhancement. Histopathology revealed an anomalous blood vessel proliferation consistent with angiomatosis. An associated chronic subdural hematoma caused severe cerebellar and brainstem compression, foramen magnum herniation, and obstructive hydrocephalus. This represents the first report of occipital bone angiomatosis with concomitant subdural hematoma in a cat.