Teaching Case

A 31-year-old man who was referred to MRI due to increasing ataxia, hypacusis, and dysarthria. 13 years ago he had undergone surgery of a cerebellar ependymoma followed by radiation therapy and chemotherapy.

The patient was admitted to our hospital with increasing cerebellar symptoms. There was no clinical evidence for subarachnoidal hemorrhage. 13 years ago a cerebellar ependymoma had been successfully resected and a ventriculoperitoneal shunt system had been implanted before followed by radiation treatment and chemotherapy. He developed slowly progressive gait unsteadiness, hearing loss, and slurred speech during the past two years. The clinical examination revealed bilateral hearing difficulties and dysarthria, but no other abnormalities of the cranial nerves. Mental status was normal. Neurological examination confirmed sensorineural hearing loss. The gait was widebased ataxic; Romberg's sign and Unterberger manouver were positive. No symptoms of dementia were detected by neuropsychological testing. Lumbar puncture was performed revealing a slightly xanthochromic cerebrospinal fluid (CSF) with an increased number of red blood cells. There were 2% eosinophiles indicating chronic irritation and 2% siderophages indicating chronic bleeding. The total protein level was increased (960 mg/dl). Ferritin in the CSF was increased by a factor of 20 (66.8 mg/l; reference 1.65 mg/l); the iron level was 2.0 mg/l (reference 1.6±1.2 mg/l). MR imaging was performed on a 1.5 T MR scanner (Siemens Vision plus, Erlangen, Germany) and demonstrated typical postoperative changes due to a previous suboccipital craniectomy. T2-weighted sequences (TR 7400ms, TE 115ms) of the brain revealed a dark rim of signal intensity representing hemosiderin outlining the cerebellar vermis and hemispheres surface bordering the subarachnoid cisterns (Fig. 1). The hypointense signal covering the brainstem consistent with superficial siderosis were especially prominent on T2*-w echo planar images (TR 1200ms, TE 52ms; Fig. 2). These changes were hardly visible on T1w images (TR 575ms, TE 14ms). Additionally, cerebellar atrophy was visible. No hydrocephalus was documented. No recurrence of the ependymoma was evident even after administration of GdDTPA (0.1mmol/kg body weight, Magnevist, Schering, Berlin, Germany). MRI of the spine showed neither signs of tumor recurrence nor superficial siderosis. A vascular malformation was excluded by angiography.

Superficial siderosis of the CNS has been considered to be a rare condition. The most common reported clinical symptoms are hearing impairment (95%), cerebellar ataxia (88%), pyramidal signs (76%), dementia (24%), anosmia (17%), anisocoria (10%), and sensory signs (13%). Less frequent symptoms include backache and lower motor signs (5-10%). Two types of superficial siderosis are described in the literature: idiopathic and secondary superficial siderosis with and without documented sources of bleeding, respectively [1]. The common sources of subarachnoidal bleeding causing superficial siderosis are dural abnormalities, vascular lesions, and tumors, as well as posttraumatic or postsurgical lesions. Neonatal superficial siderosis has been described with striking MR findings secondary to a single massive intraventricular hemorrhage [2]. Although superficial siderosis is considered an uncommon late complication of childhood cerebellar tumor, its incidence is underestimated. The diagnosis should be especially considered in patients who present with slowly developing hearing loss and ataxia many years after surgery [3]. Increased numbers of red blood cells, an increased level of siderophages, xanthochromia, and high concentrations of proteins in the CSF support the diagnosis, however MRI appears superior to confirm the diagnosis. The hypointense rim typically seen on T2w images and coating the cerebellum, brainstem, cranial nerves, cerebral hemispheres and/or spinal cord is produced by the strong magnetic susceptibility effect of iron. This effect is more pronounced at T2*w sequences. Some authors described hyperintense patterns on the surface of the brain on T1w sequences in the same distribution as the T2w hypointensities suggesting the presence of different stages of blood products [4]. The cause of the chronic subarachnoidal bleeding is uncertain in the presented case. Surgery may have caused bleeding in the brain with access to the CSF. On the other hand, radiotherapy may have been responsible in the pathogenesis of superficial siderosis. Chronic subarachnoid hemorrhage leads to chronic exposure of hemoglobin and its breakdown products. Iron in the form of ferritin is highly toxic and may cause neural death and reactive gliosis. Astrocytes and microglia are responsible for the uptake of excessive CSF iron in superficial siderosis. Over time, the iron pigments infiltrate the underlying neural tissue and may, in turn, result in necrosis of the crest of the cerebellar folia and the vermis. Although superficial siderosis is usually irreversible, diagnosis helps to avoid an unnecessary search for other causes of the patient's symptoms. The optimum treatment would be an ablation of the bleeding source, but like in our patient, no source is detected in most cases. Chelation of iron with desferroxiamine or trientene may reduce CSF iron levels but clinical improvement often remains unsatisfactory. Larger studies are certainly necessary to prove whether an early diagnosis of superficial siderosis using MRI followed by therapy with chelates prevents development of clinical symptoms in these patients.