Infratentorial Superficial Siderosis: Classification, Diagnostic Criteria, and Rational Investigation Pathway

Central nervous system infratentorial superficial siderosis (iSS) is increasingly detected by blood-sensitive magnetic resonance imaging (MRI) sequences. Despite this, there are no standardized diagnostic criteria, and the clinicalradiological spectrum, causes, and optimum investigation strategy are not established. We reviewed clinical and radiological details of patients with iSS assessed at a specialist neurological center during 2004-2016 using predefined standardized radiological criteria. All imaging findings were rated blinded to clinical details. We identified 65 patients with iSS, whom we classified into 2 groups: type 1 (classical) and type 2 (secondary) iSS. Type 1 (classical) iSS included 48 patients without any potentially causal radiologically confirmed single spontaneous or traumatic intracranial hemorrhage, of whom 39 (83%) had hearing loss, ataxia, or myelopathy; type 2 (secondary) iSS included 17 patients with a potentially causal radiologically confirmed spontaneous or traumatic intracranial hemorrhage, of whom none had hearing loss, ataxia, or myelopathy. Of the patients with type 1 (classical) iSS, 40 (83%) had a potentially causal cranial or spinal dural abnormality, 5 (11%) had an alternative cause, and 3 (6%) had no cause identified. Intraarterial digital subtraction angiography did not identify any underlying causal lesions for type 1 iSS. Type 1 (classical) iSS, defined using simple radiological criteria, is associated with a characteristic neurological syndrome. Rational investigation, including spinal MRI, nearly always reveals a potential cause, most often a dural abnormality. Catheter angiography appears to be unhelpful, suggesting that classical iSS is not associated with macrovascular arterial pathology. Recognition of type 1 (classical) iSS should allow timely diagnosis and early consideration of treatment.