Dural and Meningeal Pathologies

Summary of Key Points

Small dural defects can lead to devastating neurological disease.
Superficial siderosis, spinal cord herniation, spontaneous intracranial hypotension, and segmental amyotrophy represent a continuum of disease secondary to dural deficiencies and can present as distinct pathological entities or in combination.
Superficial siderosis is characterized by hemosiderin deposition in the subpial layers of the brain and spinal cord and presents with sensorineural hearing loss and progressive cerebellar ataxia.
Spinal cord herniation involves transdural herniation of the spinal cord, most commonly at the thoracic level through an anterior defect.
Spontaneous intracranial hypotension may be caused by a dural defect, which can be adjacent to spiculated osteophytes, that allows cerebrospinal fluid to leak into the epidural space, often causing disabling headaches and potentially ataxia, cognitive impairment, diplopia, and abnormalities of hearing and taste.
Segmental amyotrophy can be caused by an extra arachnoid fluid collection secondary to an anterior dural defect, which often causes compression of the spinal cord.
The definitive treatment for these pathologies is locating the dural deficiency and performing targeted surgical repair.

The meninges in the brain and spinal cord consist of three layers: the dura mater, arachnoid mater, and pia mater. The brain has two layers of dura, the outer periosteal and the inner meningeal layer, that are fused together except where they separate and form venous sinuses. As the dura descends toward the foramen magnum, the two layers separate, and the outer layer forms the periosteum of the spinal canal, and the inner layer forms the dural sac surrounding the spinal cord and nerve roots. Defects in this single, relatively thin layer of dura can be asymptomatic or can have devastating neurological consequences, and represent the scope of this chapter.

The resultant pathologies presented here can present in combination or along a continuum. An example is a patient that had a dural defect causing hypotensive headaches that resolved once the patient developed Brown–Sequard syndrome. This was attributed to the cerebrospinal fluid (CSF) leak being sealed off by spinal cord herniation.

Superficial Siderosis

Epidemiology

Superficial siderosis (SS) is characterized by hemosiderin deposition in the subpial layers of the brain and spinal cord. It is a rare disease, although with the advent of magnetic resonance imaging (MRI) it is increasingly recognized. A population-based study of 1412 participants aged 50 to 89 years reviewed MRI scans and found that only 13 (0.92%) of patients had cortical SS, and two (0.14%) had infratentorial SS. When stratified by age, the frequency of SS was higher in those over the age of 69 years (1.89%) compared with those aged 50 to 69 years (0.39%). The estimated population prevalence was 0.56% in those aged 50 to 89 years and approximately 1% in people over the age of 70 years. Another population study by Vernooij et al. reviewed MRI scans from 1062 participants aged 60 to 96 years (mean 69 years) and found only seven (0.7%) to have signs of SS. All seven of these participants had evidence of microbleeds in the vicinity of the SS, and none showed any signs of macrobleeds, brain tumors, or vascular malformations. Most of this data is in the setting of cerebral amyloid angiopathy, which is more common than SS and is directly attributed to spinal dural defects.

Pathophysiology

SS is caused by slow and chronic low-volume hemorrhage into the subpial space of the brain and/or spinal cord, resulting in hemosiderin deposition and a resultant brownish discoloration of the leptomeninges and parenchyma. The underlying etiology for SS was historically very difficult to determine, with many patients having idiopathic SS. An older study showed that an underlying cause could be identified for only half of the published cases of SS at the time. With the advent of more advanced imaging techniques such as dynamic computed tomography (CT) myelograms, the underlying cause for most patients can be detected. Potential etiologies include tumors, prior intradural procedure such as tumor resection or shunt placement, root or plexus avulsions, vascular abnormalities, CSF cavity lesions such as pseudomeningoceles, and either spontaneous or inadvertent dural tears. ^, Prior trauma has been shown to be a risk factor for developing SS, with one series showing 15 of 30 patients with SS had a history of trauma. Trauma may damage small veins, making them fragile and vulnerable to future bleeds. A clinical history of acute subarachnoid hemorrhage is rare.

Classic SS is located infratentorially with hemosiderin deposits in the brainstem, cerebellum, and spinal cord. The hemosiderin ultimately causes parenchymal damage. The eighth nerve is the most common cranial nerve to be involved, which is thought to be as a result of its long glial segment predisposing it to hemosiderin deposition. The first and second cranial nerves are also frequently involved. Cortical SS is characterized by hemosiderin deposition in the cerebral convexities and has been associated with cerebral amyloid angiopathy.

Presentation

The classic and most common presentation of SS is sensorineural hearing loss and progressive cerebellar ataxia. This has been described in roughly 90% of SS cases secondary to infratentorial hemosiderin deposition. ^, Because of the preferential involvement of the vermis, gait ataxia is more common than limb ataxia. Other less common features include tinnitus, cognitive impairment, seizures, visual disturbances, and impaired smell. Usually, symptoms progress over years or even decades, with most patients presenting over the age of 40 years. Patients with cortical siderosis can present with episodic headaches and imaging consistent with subarachnoid bleeding, but most patients with dural defect related SS present with orthostatic headaches. Red blood cells (RBCs), xanthochromia, and elevated protein can be found in the CSF, although with intermittent bleeds they are sometimes not detected.

Imaging

CT is often not able to detect hemosiderin staining sufficient to diagnose SS, although rarely a hyperdense ring around the brainstem can be seen. CT can demonstrate cerebellar atrophy or an old skull fracture from a prior trauma. However, MRI is the modality of choice to diagnose SS by a rim of T2 hypointensity over the affected regions, most commonly the cerebellum, brain stem, and cranial nerves 1, 2, and 8 ( Fig. 27.1 ). The findings early in the disease process are subtle, and a high index of suspicion is required to make the diagnosis, which can be made even in asymptomatic patients. Entire neuroaxis imaging is necessary to attempt localization of a bleeding source. Gradient-echo (GRE) T2-weighted images or susceptibility-weighted images (SWI) are particularly sensitive in detecting hemosiderin deposition via hypointensity along affected areas. In patients who do not get the more sensitive SWI or GRE sequences, the hemosiderin staining may be missed, and patients can be misdiagnosed with spinocerebellar ataxia. The presence of hearing impairment is an additional clue that SS may be the diagnosis and can differentiate the disease from spinocerebellar ataxia.

Fig. 27.1, Superficial siderosis with hemosiderin deposition ( arrows ) seen as hypointensity along the cerebellum and brainstem on axial magnetic resonance imaging (MRI) with standard T2-weighted images ( A ) and gradient echo ( B ). T2-weighted gradient echo image demonstrates hemosiderin deposition within bilateral sylvian fissures ( C ). Sagittal T2-weighted MRI with gradient echo sequence shows hemosiderin along the brainstem and spinal cord ( D ).

Other potentially affected areas include the sylvian fissure, the interhemispheric fissure, the cerebral convexity, and the spinal cord (see Fig. 27.1 ). T2 hypointensity along the cauda equina along with clumping of the nerve roots can be seen, suggestive of arachnoiditis. Blood pooling in the cul-de-sac may be mistaken for a tumor or tumor seeding. SS along the ventricles is rare and, when seen, is often associated with intraventricular tumors. Cerebellar atrophy is a common finding, most marked in the superior vermis. Patients may present with a fluid collection in the spinal canal suggestive of a meningocele or pseudomeningocele that may be the source of bleeding. ^, Cerebral angiography, whether conventional or performed with CT or MRI, rarely detects bleeding sources, as they tend to be secondary to microtrauma to small vessels in the meningocele or pseudomeningocele cavity.

CT myelography can be a useful in identifying dural defects often not apparent on MRI, including in patients with dural diverticula and pseudomeningoceles. They can also identify nerve root avulsions with associated dural deficiencies. These defects can be a source of bleeding in SS and may be amenable to surgical repair. Dynamic CT myelography is a technique that can detect high-flow leaks by scanning the entire spine immediately after injection of intrathecal contrast. This can be useful in the setting of extensive intradural fluid collections and may identify a defect target for surgical repair. Slow-flow leaks can be especially challenging, and additional techniques to detect them include delayed CT scanning, positive pressure myelography (injection of saline before contrast), and gadolinium myelography.

Treatment and Outcome

Given the progressive nature of SS, active bleeding sites and suspected dural defects should be investigated and treated, if possible. In one series of 30 patients with SS, only seven patients had a suspected bleeding source identified that that was amenable to intervention, which included tumor or vascular malformation excision and repair of pseudomeningocele or other dural defects. A CSF venous fistula may also be a cause of SS, and the indicated treatment would be ligation of the fistula. Postsurgical CSF examination can confirm obliteration of the source of bleeding with resolution of xanthochromia and/or RBCs. The most common outcome of successfully treated SS is cessation of disease progression, although some studies have shown that patients can improve clinically, radiographically, and/or in their CSF studies. Early diagnosis and prompt intervention of SS may halt progression of the disease and provide clinical improvement in some cases. Long-term follow-up is indicated to ensure treatment durability.

Spinal Cord Herniation

You're Reading a Preview

Become a Clinical Tree membership for Full access and enjoy Unlimited articles

Become membership

If you are a member. Log in here