European Journal of Neurology 2007, 14: e2–e3 doi:10.1111/j.1468-1331.2007.01716.x LETTER TO THE EDITOR Superficial siderosis of the CNS: selective central myelin vulnerability and peripheral myelin sparing demonstrated by MRI M. Grisoli, E. Maccagnano, T. De Simone and M. Savoiardo Department of Neuroradiology, Istituto Nazionale Neurologico ÔC. BestaÕ, Milano, Italy The distribution of SS explains the common clinical presentation which mainly consists of deafness and ataxia (the crowns of the cerebellar folia may be destroyed), followed by signs of myelopathy and, in advanced cases, dementia. The first cranial nerve involvement is often overlooked because its function is rarely tested; the optic nerve is involved in its peripheral fibers [4] and visual function is usually spared [3,4]. The immediate transition to peripheral myelin in the other cranial nerves and spinal roots prevents their clinical involvement [4]. These findings are demonstrated in brain and complete spine MRI study (Fig. 1) that has been obtained in a 47-year-old woman who presented at age 41 with progressive Correspondence: Dr Marina Grisoli, Department of Neuroradiology, Istituto Nazionale Neurologico ÔC. BestaÕ, Via Celoria 11, Milano, Italy (tel.: +39 02 2394 2449 or +39 02 2394 2451; fax: +39 02 2394 2543; e-mail: mgrisoli@istituto-besta.it). Keywords: ataxia, deafness, magnetic resonance imaging, superficial siderosis Received 8 September 2006 Accepted 13 December 2006 Magnetic resonance imaging (MRI) has greatly facilitated the diagnosis of superficial siderosis (SS) of the central nervous system (CNS) caused by magnetic susceptibility effects of iron causing loss of signal intensity in T2-weighted images. Thin sections and increased resolution now allow demonstration of details in the involvement of the cranial nerves and spinal roots that have only been demonstrated in pathological studies [1,2]. Their recognition refreshes our knowledge of the pathogenesis of this disorder, linked to presence of glial cells and sparing of peripheral myelin. Superficial siderosis results from deposition of blood derivatives on the surface of the CNS from repeated subarachnoid microhemorrhages in patients with tumors, vascular malformations, irregularly scarred post-surgical, or traumatic dural lacerations. In nearly half the cases, the origin may remain unknown [3,4]. The tissue damage ensues conversion of heme to ferritin and hemosiderin and requires an active glial process [5]. Therefore, SS only occurs where there is central myelin. Olfactory tract and bulb and optic nerves are involved because they are part of the CNS. The eighth nerve is affected because in this nerve the transition from central to peripheral myelin, formed by Schwann cells, is 10–15 mm away from the entry zone. The other cranial nerves and spinal nerve roots are involved only for 1–2 mm, because of a very proximal transition from central to peripheral myelin [1]. e2 Figure 1 Magnetic resonance imaging (MRI), T2-weighted images. (a) Hypointensity caused by siderosis is present along the acoustic nerve (arrows), whereas the seventh (arrowhead) is spared. (b) Hypointensity of the trigeminal nerves is limited to 1 or 2 mm, close to the entry zone (arrows). No clinical involvement of the fifth nerves was present. The surface of brainstem and cerebellum is hypointense because of extensive superficial siderosis (SS) (a–c). Coronal and axial spinal MRI demonstrates involvement of the spinal cord surface and sparing of the cauda equina (d, e). Ó 2007 EFNS Letter to the Editor neurosensory hearing loss and ataxia of 3-year duration. No history of previous trauma or neurosurgery was obtained. Superficial siderosis was diagnosed by MRI and cerebrospinal fluid examination. The source of microhemorrhages has not been found. Magnetic resonance imaging shows in vivo the selective vulnerability of central myelin and sparing of peripheral myelin in cranial nerves and spinal roots, accounting for the clinical presentation of SS. References 1. Koeppen AH, Dentinger MP. Brain hemosiderin and superficial siderosis of the central nervous system. Journal of Neuropathology and Experimental Neurology 1988; 47: 249–270. 2. Friede RL. Developmental Neuropathology, 2nd edn. Berlin Heidelberg New York: Springer, 1989. Ó 2007 EFNS European Journal of Neurology 14, e2–e3 e3 3. Kumar N, Cohen-Gadol AA, Wright RA, Miller GM, Piepgras DG, Ahlskog JE. Superficial siderosis. Neurology 2006; 66: 1144–1152. 4. Bracchi M, Savoiardo M, Triulzi F, et al. Superficial siderosis of the CNS: MR diagnosis and clinical findings. AJNR American Journal of Neuroradiology 1993; 14: 227–236. 5. Koeppen AH, Dickson AC, Chu RC, Thach RE. The pathogenesis of superficial siderosis of the central nervous system. Annals of Neurology 1993; 34: 646–653.