LAUSR

Dear Editor, A 54-year-old woman presented with subacute spastic and ataxic paraparesis. Sensorineural hearing loss had required a cochlear implant 5 years previously. Laboratory tests for coagulation, liver/kidney functions, and blood ion concentration were all unremarkable. MRI detected a leptomeningeal hemosiderin deposit in the neuraxis (Fig. 1a–d). A spinal epidural fluid collection and dural defect at the T2-T4 level were identified onMR-myelography (MR-m) and ultrafast dynamic CT myelography (ud-CTM) (Fig. 1 e–i). Therefore, superficial siderosis, due to a spinal dural tear, was diagnosed, and subsequent surgical repair was performed, with small sutures and a muscle graft. Superficial siderosis (SS) of the central nervous system (CNS) is due to hemosiderin deposition in the subpial layers of the brain and spinal cord [1], and it is a consequence of recurrent and persistent bleeding into the subarachnoid space. The source of the bleeding often remains undetected, despite extensive neuroimaging. Tumors such as ependymoma, meningioma, oligodendroglioma, pineocytoma, and paraganglioma have been reported in 35% of cases, while vascular abnormalities such as arteriovenous malformations or aneurysms were present in 18% of cases. A previous history of trauma or intradural surgery is a possible finding. Extraarachnoid longitudinally extensive intrathecal fluid-filled collection has frequently been noted in SS patients. The brain’s ability to biosynthesize ferritin and hemosiderin, a defensive mechanism in response to a prolonged hemoglobin iron overload, is an important etiopathogenetic factor in SS. The gliosis and neuronal loss associated with ferritin and hemosiderin deposition may result in an increased signal intensity in the adjacent nervous tissue. Indeed, hemosiderin formation occurs mainly within the microglia, as it can synthesize ferritin so that hemosiderin is taken up selectively by CNS areas rich in microglia and/or by those close to the cerebrospinal fluid (CSF) flow [2]. Notably, the 8th cranial nerve may be considered vulnerable as it is not only particularly rich in microglia, but also, before entering the internal acoustic canal, it travels a relatively long distance outside the brain and is exposed to the damaging effects of a chronic subarachnoid hemorrhage within the CNS. The classical clinical presentation of SS includes adult onset of slowly progressive gait ataxia with cerebellar dysarthria and sensorineural hearing impairment. CT myelography (CTM) may identify a dural defect connecting the intrathecal space to the fluid-filled collection. In CTM, the introduction of iodinated contrast medium (ICM) into the thecal sac allows for specific visualization of the CSF, including the one that has leaked into the epidural space [3]. In cases of high-flow CSF leaks, the contrast agent may spill so quickly from the thecal sac that by the time the images are acquired, myelographic ICM may have spread widely into the epidural space, making a precise localization of the bleeding source almost impossible. However, the ud-CTM, a technique previously described by Thielen and Luetmer [4], provides a sufficient temporal and spatial resolution to overcome this shortcoming and can also detect high-flow leaks. These leaks form a Bfork^ or Bsplitlike^ shape in the column of the flowing myelographic ICM, where the extra-arachnoid ICM continues to flow downwards in a cranial direction. MR-m can also be used to evaluate CSF leaks. A leak on an MR-m is evidenced by a hyperintense fluid collection (T2w) in the epidural space. Heavily T2weighted imaging (steady-state sequences) has been explored to obtain images with a greater contrast between the CSF and background tissues [5]. Compared with CTM, MR-m has the * Nicola Morelli [email protected]