Ataxia telangiectasia (AT) is a rare autosomal recessive neurodegenerative multisystem disorder caused by two truncating ATM gene mutations leading to total loss of ATM kinase activity and, therefore, function of the ATM protein ¹. In less severe cases, termed AT variants, there is retention of some ATM kinase activity due to either expression of very low levels of normal ATM protein (from splice site mutations) or expression of mutant ATM (from missense mutations) ².

AT variants are a phenotypically heterogeneous group, characterized by slower progression of clinical signs, an extended lifespan compared to most patients with the classical form of the disease with less cellular sensitivity to radiation, susceptibility to malignancies and recurrent sinopulmonary infection.

In the absence of clinical history, this case demonstrates a radiologic diagnostic conundrum. The most striking abnormality is the presence of diffuse bilateral microhemorrhages with a superimposed acute intraparenchymal hematoma and cerebral amyloid angiopathy would be high on the list of differentials. However, the presence of extensive bilateral T2/FlAIR hyperintense signal within the white matter seems disproportionate to the degree of likely concomitant small vessel disease. Given that this is a case of an adult brain, the diagnosis of AT may elude the radiologist as patients with the classic form of AT usually do not survive beyond childhood. The presence of diffuse white matter T2/FLAIR signal abnormality and disproportionate cerebellar atrophy clinches the diagnosis of variant ataxic telangiectasia.