Neuroradiology

Neurosarcoidosis

Sarcoidosis is a multisystem granulomatous disorder of unknown origin. Involvement of the CNS ranges from 4 - 9%; nearly half of patients are asymptomatic. Systemic manifestations usually arise first, and neurological signs develop during the course of the disease. Primary manifestations of the CNS are more rare.

The most common CNS manifestations are meningeal sarcoidosis and parenchymal sarcoidosis. Spinal cord, both intra- and extramedullary, and peripheral nerves may also be involved. Another location in the head is the orbit where the ocular globe, conjunctiva, extraocular muscle, retrobulbar fat and lacrimal gland may be affected.

Meningeal sarcoidosis often occurs at the skull base (Fig.1) and involves the optic chiasm, the pituitary gland, the floor of the third ventricle, and the hypothalamus. Cranial nerve neuropathy is the most common neurological sign; hypothalamic/pituitary dysfunction such as diabetes insipidus occurs not infrequently as a result of infundibular involvement. Hydrocephalus may also be found.

Cross-sectional CT studies may document diffuse or focal meningeal thickening that enhances strongly after contrast administration. MRI better depicts the involvement and enhancement in the basal cisterns and related structures such as chiasm, cranial nerves and hypothalamic infundibulum.

Parenchymal sarcoidosis appears as homogeneously enhancing isolated or multiple nodules, or as a ring-like enhancement around iso-hyperintense nodules. It can occur in any part of the brain.

Periventricular and subcortical white matter abnormalities that may resemble multiple sclerosis have been reported in sarcoidosis. They appear as areas of low density on CT but are much better demonstrated on MR as areas of high intensity on T2-weighted and of low intensity on T1-weighted images. No enhancement is usually seen. Occasionally extension into the periaqueductal region is found. These changes may represent ischaemia associated with vasculitis or infiltration of subependymal sarcoid granulation tissue.

Differential diagnosis based on radiological apperance includes chronic meningitis (fungal, tubercolus, luetic) and possibly meningeal seeding.

 

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Fig.1

a, b. MR, T1-weighted images. Slight thickening of the infundibulum, hypothalamus and intracranial optic nerves. c, d. MR, T1-weighted images following gadolinium injection. Marked enhancement of the basal cisterns and meninges as well as of the thickened hypothalamus. e, f. MR, T2-weighted images fail to show significant abnormalities.
Neurosarcoidosis, Fig.1 (a)
Neurosarcoidosis, Fig.1 (b)
Neurosarcoidosis, Fig.1 (c)
Neurosarcoidosis, Fig.1 (d)
Neurosarcoidosis, Fig.1 (e)
Neurosarcoidosis, Fig.1 (f)