Superficial siderosis and spinal intradural extramedullary cavernous angioma.

Abstract

Superficial siderosis results from hemosiderin deposition in the subpial layers of the brain and spinal cord. The chronicity of bleeding is indispensable for the development of siderosis; the condition cannot occur after a single bleeding episode. Extensive deposition of hemosiderin on the surface of cells of the central nervous system (CNS) induces neurological dysfunction (1, 2). Superficial siderosis is clinically diagnosed based on the detection of signal loss at the surface of CNS structures on T2-weighted MRI (3). T2 * weighted MRI is now available for detecting small amounts of iron deposition with greater sensitivity (4). This disease was previously considered to be rare; however, it has recently become more frequently diagnosed in patients with progressive sensorineural hearing loss (5). The auditory nerve, cerebellum and brainstem are likely to be involved in patients with superficial siderosis, resulting in the classic triad of sensorineural hearing loss, cerebellar ataxia and pyramidal tract symptoms (1, 2). The cerebellar cortex is also susceptible to hemosiderin deposition (6). The special vulnerability of the auditory nerve is attributed to the long course of this nerve covered by central myelin in the subarachnoid space (7). Various pathologies have been reported to be possible causes of superficial siderosis. For example, Levy et al. reviewed 270 patients and reported that the underlying causative disorders in these subjects included CNS tumors (21%), trauma (13%), arteriovenous malformations (9%), a post-surgical status (7%) and idiopathic causes (35%) (1). Ependymoma is regarded to be the dominant histological type of tumor of superficial siderosis (2), while spinal intradural extramedullary cavernous angioma is an extremely rare cause of this disease. Cavernous angioma involves vascular malformations created by anomalous vessels without interposition of neural tissue. The typical MRI features include well-defined lesions with mixed signal intensity on both T1- and T2-weighted images, often surrounded by a hypointense ring on T2weighted images, due to hemosiderin deposition (8). Histologically, cavernous angioma consists of large, dilated hyaline vascular channels arranged in a diffuse pattern. These lesions are often associated with thrombosis, perivascular hemosiderin deposition and calcification (9). Cavernous angioma can occur anywhere in the CNS, although these lesions favor the cerebral hemisphere (10). Spinal cavernous angioma involves rare vascular malformations occurring primarily in the vertebral body with or without extradural extension. Only 3% of cavernous angiomas are reported to be intradural (11). Intradural extramedullary cavernous angioma lesions are more rare than corresponding intramedullary lesions. Most cases of intradural-extramedullary cavernous angioma present with symptoms related to spinal cord compression, such as sensorimotor deficits, back pain and/or sphincter dysfunction. Only one case of superficial siderosis (12) and two cases of hydrocephalus (13, 14) have been reported. In this issue of Internal Medicine, Katoh et al. (15) report a case of spinal intradural extramedullary cavernous angioma presenting with superficial siderosis and hydrocephalus. Their patient, with a past history of spontaneous severe headache 11 years earlier, visited an otorhinolaryngologist complaining of a three-year history of progressive bilateral hearing impairment. A neurological examination revealed bilateral sensorineural hearing impairment, hyperreflexia in all limbs, mild ataxia and mild cognitive dysfunction, although no symptoms related to spinal cord compression were observed. Because superficial siderosis and hydrocephalus are the ultimate consequences of chronic bleeding, long-term damage resulting from delayed diagnosis may have made the patient’s neurological deficits irreversible. Clinicians should therefore keep in mind superficial siderosis as an important cause of bilateral hearing impairment and perform