Superficial siderosis associated with duplicated dura mater detected by CISS reverse MRI

Superficial siderosis (SS) of the central nervous system is a rare disease caused by chronic or repeated hemorrhages in the subarachnoid space. Closure of dural defects is an effective therapy for SS. Conventional magnetic resonance imaging (MRI), however, cannot sufficiently detect dural tears. To better detect these defects, we analyzed the clinical data of consecutive patients admitted to our department with SS and performed constructive interference in steady-state (CISS) reverse MRI of the brain and spinal cord. CISS reverse method emphasizes the contrast between the dura and cerebrospinal fluid, enabling detection of dural defects better than usual T2-weighted MRI. CISS reverse MRI detected fluid-filled collections in five of the seven SS patients we studied. These images showed that the fluid-filled collections were packed within duplicated dura mater. In three of the five, dural defects were confirmed intraoperatively. We postulate that fluid-filled collections are actually derived from dissection of the dura mater. In accordance with the Monro-Kellie hypothesis, we propose that CSF transferal into the fluid-filled collections via dural defects induces an increase in blood volume and promotes the exudation of blood from engorged vessels. In patients with SS, it is very important to repair dural defects to prevent further associated neurological impairment. CISS reverse MRI is useful for detecting such dural defects.