Demyelinating Disease

CHAPTER 152 Demyelinating Disease

Although typically seen in the neurology rather than neurosurgery clinic, some patients with demyelinating disease come to the threshold of surgery or beyond. Mass effect, perilesional edema, and contrast enhancement may all suggest a neoplasm; biopsy or resection (or both) may be undertaken, sometimes even in the presence of multiple lesions in sites favored by multiple sclerosis. A frozen section diagnosis of glioma may endorse “tumor” resection, with its attendant risk for neurological deficits. If the pathologist’s impression is “confirmed” on permanent sections, radiotherapy and chemotherapy, also with their potential complications, may be undertaken. Malpractice actions, in which blame is often cast widely, have been known to follow.

There is thus no better example of the need for caution in the preoperative diagnosis of central nervous system (CNS) lesions than with demyelinating disease.¹ The diagnosis of grade II infiltrating glioma (astrocytoma, oligodendroglioma, or mixed glioma) in a patient with an enhancing lesion is almost by definition contradictory because these low-grade tumors are nonenhancing. In the event of such discordance, the pathologist can re-review the slides, and the neuroradiologist might revisit the images. “Could this be demyelinating disease?” Ideally, any clinical suspicions about demyelinating disease are relayed to the pathologist at the time that the specimens are delivered, but the pathologist needs to consider demyelinating disease without prompting because there are often few, if any such clinical suspicions in biopsied lesions, particularly when solitary.

The chance that such lesions will be subjected to biopsy can be minimized by an interdisciplinary approach that mandates full consideration of non-neoplastic diseases before the diagnosis of a tumor is accepted.² This should be done even in the face of an ominous contrast-enhancing mass, for which tumor is the neurosurgeon’s visceral impression.

Clinically, demyelinating disease is a set of diseases whose protean expressions overlap with those of other entities, including gliomas. At one end of a broad spectrum are patients with incrementally accumulating expression of multiple lesions at classic sites, such as the optic system, brainstem, spinal cord, and cerebral hemispheres. At the other end are patients with an isolated, unifocal mass for which demyelinating disease may be low in the differential diagnosis. Demyelinating disease should be considered for scenarios at both ends of the spectrum, as well as for those in between. Although it usually occurs in young adults, demyelinating disease—or at least reactive macrophage-rich lesions—is not rare in demographic outliers who are seemingly too young or too old for such a disease.

Neuroradiologically, demyelinating disease has both quantitative and qualitative features that aid in identification. Magnetic resonance imaging (MRI) has revolutionized the diagnosis; several MRI features are believed to be suggestive. Classic demyelinating plaques are typically T2 hyperintense and located within the periventricular white matter of the corona radiata and centrum semiovale (Fig. 152-1). In addition, the lesions are usually ovoid with their main axis perpendicular to the corpus callosum and parallel to the course of the intramedullary cerebral veins. These so-called Dawson’s fingers result from the fact that such plaques are predominantly perivenular (see Fig. 152-1

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