Exercise: White Matter Diseases

EXERCISE 12-7. WHITE MATTER DISEASES

12-16. In Case 12-16, what is the most likely diagnosis (Figure 12-36 A, B)?

A.         Pseudotumor cerebri

B.         Metastatic disease

C.         Septic emboli

D.         Radiation necrosis

E.         Multiple sclerosis

12-17. In Case 12-17, what is most likely responsible for the abnormalities seen on the MR image (Figure 12-37 A, B)?

A.         Cardiac arrhythmia

B.         Chronic hypertension

C.         Remote trauma

D.         Hepatic failure

E.         Carbon monoxide poisoning

Radiologic Findings

12-16. In this case, sagittal T1-weighted and axial FLAIR MR images (Figure 12-36 A, B) show multiple foci of abnormal signal within the periventricular white matter (arrows). These lesions are quite characteristic of multiple sclerosis (E is the correct answer to Ques-tion 12-16). The patient’s visual difficulties were due to optic neuritis, a common abnormality in multiple sclerosis.

12-17. In this case, there are patchy areas of increased T2 sig-nal (arrows) within the periventricular white matter(Figure 12-37). Usually seen in elderly hypertensive patients, these lesions correspond to focal areas of de-myelination secondary to deep white matter ischemia (B is the correct answer to Question 12-17). 

Discussion

Diseases that primarily affect the cerebral white matter have a host of causes. Unfortunately, very few of these conditions have specific appearances on CT or MR scans. Neuroimaging is usually performed to determine whether there are changes within the brain that are compatible with one of the white matter diseases and to rule out other conditions that might mimic white matter disease.

White matter diseases include both inherited and ac-quired conditions. They can be further subdivided into de-myelinating conditions (destruction or injury of normally formed myelin) and dysmyelinating conditions (abnormal formation or maintenance of myelin, usually because of an enzyme deficiency). The dysmyelinating conditions are rare and, for the most part, include the leukodystrophies, such as adrenoleukodystrophy and metachromatic leukodystrophy. Although the MR appearance can be striking in some of these diseases, it is often nonspecific. These conditions are not dis-cussed here.

Multiple sclerosis (MS) (Case 12-16) is the most common demyelinating disease. Because there is no generally accepted etiology for MS, it is also referred to as a primary demyelinat-ing disease. Secondary demyelinating conditions are those caused by a known agent or event. MS usually occurs in young adults and more often in women than men (approxi-mately 2:1). The disease is characterized by a relapsing and remitting course and by varying neurologic symptoms, de-pending on the location of the lesion within the CNS. Al-though diagnosis of MS is usually based on clinical criteria, MR imaging can be a very helpful confirmatory test. Typical MS plaques appear as ovoid, T2 signal hyperintensities within the periventricular and deep white matter. Lesions are also common within the corpus callosum, brainstem, cere-bellar peduncles, spinal cord, and optic nerves. MS plaque enhancement on gadolinium-infused MR images suggests active disease (ie, breakdown of the BBB). Confluent areas of T2 signal abnormality in the periventricular white matter are common in severe cases.

Ischemic demyelination (Case 12-17) is usually seen in patients with small-vessel disease (such as from long-stand-ing hypertension). This condition, also called leukoaraiosis (white matter softening), occurs because of hypertension-in-duced arteriolar sclerosis of penetrating medullary arteries that supply the deep white matter of the brain. This leads to a reduction in white matter blood flow with accompanying is-chemic demyelination. This condition occurs most com-monly in older patients and is associated with small-vessel brain infarcts (lacunar infarcts). MR imaging usually demon-strates patchy areas of increased T2 signal in the deep white matter. The lesions are often bilaterally symmetric and periventricular in distribution.