Superficial and intraventricular siderosis following resection of an intraventricular tumour

A 40-year-old male presented with gradually worsening ataxia, headaches, visual blurring and hearing loss. He was operated for an intraventricular tumour 5 months back. On examination, he exhibited cerebellar signs - broad-based gait, difficulty in making a turn and Romberg’s positive test. Audiometry showed sensorineural pattern of hearing loss in both ears. Patient did not have the symptoms prior to the surgery. Operative and post-operative records indicated that the lesion was vascular. Patient had a complicated post-operative stay with an intraventricular drain in post-operative period, which yielded blood-stained output. Histopathological examination of the tumour revealed to be a central neurocytoma.

Contrast-enhanced MR examination of the brain was performed.

Axial T2W (Figure 1) and T1 post-contrast (Figure 2) images show a lobulated T2 hypointense enhancing intraventricular lesion (black arrows) along the septum pallucidum. The left lateral ventricle is dilated and shows intraventricular adhesions (black asterisks) and trapping of the left frontal horn due to adhesions.

Sagittal T2W image (Figure 3) shows intraventricular T2 hypointense midline lesion (black arrow). Gliosis and encephalomalacia is seen in frontal lobe due to previous operative intervention. Marked cerebellar atrophy is seen. Surface of the brainstem and upper cervical cord shows T2 hypointense layering (white arrows).

Axial T2W image (Figure 4) at the level of superior cerebellar peduncles shows T2 hypointense layering (white arrows) over the surface of cerebral cortex, brainstem and cerebellar folia. Folia spaces are widened due to cerebellar atrophy.

Axial susceptibility weighted imaging - SWI (Figures 5 and 6) show blooming in the intraventricular mass (white arrow). Extensive areas of surface blooming are seen over the para-midline and convexity cortical surface (black arrows) and Sylvian fissures. Blooming is seen along ependymal lining of left lateral ventricle.

Axial SWI image (Figure 7) shows blooming over the cisternal segments of bilateral trigeminal nerves (white arrows) and over the cerebellar folia (black arrow).

Axial SWI image (Figure 8) shows blooming over the cisternal segments of bilateral 7^th-8^th nerve complexes (white arrows), brainstem and over the cerebellar folia (black arrow).

The findings of surface blooming along the intracranial structures were absent prior to the surgery, supporting the hypothesis that the source of blood products was the bleeding during the surgery.

Background

Repeated intracranial bleeding leads to deposition of blood products in the subarachnoid space and ventricles. Source of bleeding can be a ruptured aneurysm, a previous surgery, intracranial haemorrhage due to trauma or a tumour. Blood products eventually degrade into hemosiderin. Superficial siderosis is deposition of hemosiderin over the superficial and subpial layers of the brain, cranial nerves and spinal cord. This leads to hypertrophy and hyperplasia of microglia. Microglia cells can synthesize ferritin after prolonged contact with blood degradation products and Iron. Ferritin synthesis is more pronounced in cerebellar Bergmann glial cells, which may be responsible for marked cerebellar involvement [1,2].

Ferritin synthesis is aimed to bind free iron and protect the neural tissue from damage inflicted by contact with toxic-free radicle damage due to iron exposure. Repeated chronic bleeding surpass the capacity of microglial protective mechanism and lead to neural damage and degeneration [1,2,3].

Hemosiderin deposits in superficial siderosis form a brown yellowish layer over the surface of neural structures. Since blood products settle down in basal subarachnoid spaces and posterior fossa due to gravity, siderosis has predilection to involve cerebellar vermis, folia, brainstem, basal frontal and temporal surfaces, cranial nerves surfaces and spinal cord surface. Cranial nerve involvement at junction of peripheral Schwann cells layer and central glial layer is responsible for nerve irritation and symptoms related to nerve dysfunction [3].

Clinical perspective

Clinical diagnosis of superficial siderosis can be a challenge due to myriad of clinical symptoms with poor localization. Siderosis deposits can occur over multiple locations at brain surface, leading to involvement of multiple functional areas. Most common symptoms are related to cerebellar involvement – gradually progressive ataxia broad-based gait and dysarthria. Involvement of cranial nerves lead to ocular palsies, trigeminal neuropathy and sensorineural hearing loss. Spinal cord involvement and subsequent degeneration can lead to pyramidal signs, bladder and bowel dysfunction. Cortical cerebral involvement lead to decline in higher function such as cognition, speech and execution functions and memory recall [3].

Imaging perspective

Most important part of siderosis workup is localization of the source of bleeding. High index of clinical suspicion is needed to start the imaging workup in correct direction. Imaging workup may include MR imaging of the brain and spine. Intracranial tumours and aneurysms may lead to repeated haemorrhages and can be localized on CT and MR with angiography [3]. Another less common cause of siderosis is amyloid angiopathy in the elderly. Amyloid angiopathy can lead to progressive cognitive decline combined with symptoms of surface siderosis [4].

Gradient echo (GRE) or susceptibility weighted imaging (SWI) are mainstay to visualize the surface siderosis. T2 images can also show hypointense layering, but findings may be more subtle.

Spinal CSF leaks with longitudinal extensive spinal fluid collections are associated with superficial siderosis. Localization and treatment of the site of the dural leak require static or dynamic high-resolution CT myelography or DSA myelography. Potential source of leak may be a dural tear, CSF – venous fistulae, diverticulum, post-traumatic nerve root avulsion or a pseudomeningocele [2].

After imaging localization, treatment can be initiated to curtail the cause of bleeding. CSF leak sites can be addressed with surgery. CSF fistula can require endovascular or percutaneous targeted embolization [3].

Outcome

Patient was admitted under neurosurgery unit. Hydrocephalus was addressed with ventricular drainage. Recurrence of central neurocytoma was cause of repeated bleeding. Surgical treatment with tumour resection was done for the recurrent disease.

Take home points

Surface siderosis requires careful clinical and imaging evaluation of entire neuraxis – brain and spine to look for a source of bleed and to guide appropriate treatment.

In this case, superficial siderosis was related to a surgery for an intraventricular tumour. Similar clinical symptoms in a post-operative patient will support the clinical and radiological diagnosis of superficial siderosis.