Neuroradiology

Histiocytosis x

The term histiocytosis X has been used in the past to define a group of diseases characterized by proliferation of histiocytes (macrophages) embracing eosinophilic granuloma, Hand Shuller Christian disease and Abt Letterer Siwe disease, "X" being the unknown aetiological factor. Histiocytosis X now has been supplanted by "Langerhans' cell histiocytosis or granulomatosis (LCH)", the Langerhans' cell being the common cell in all these disorders. Because there is a great overlap between these subgroups, LCH is currently classified on the basis of its extent: as being unifocal, multifocal and disseminated.

Unifocal LCH is the most common, benign form characterized by a solitary lytic lesion of the skull or spine (eosinophilic granuloma). The multifocal form is a more aggressive disorder involving the bone and the hypothalamus or pituitary stalk and referts to the Hand Schuller Christian disease. Disseminated LCH as been referred to as Abt Letterer Siwe disease and involves skin, lymph nodes, viscera and rarely the central nervous system. Infiltrates within the CNS occur primarily in the hypothalamus, infundibulum, optic chiasm, choroid plexus and cerebral hemispheres.

LCH occurs typically in children but can develop in all age groups, with an equal sex distribution.

The most frequent neurological signs are diabetes insipidus (25% of multifocal or disseminated disease), hypothalamic dysfunction (obesity, growth retardation, hypogonadism), cranial nerve palsies, ataxia, seizures and signs of increased intracranial pressure.

Plain radiographs can only reveal osteolytic lesions, usually well defined, with a sclerotic margin.

CT can demonstrate the lytic bone lesions, and the thickening and enhancement of the CNS-involved structures particularly of the pituitary stalk. MR is the imaging modality of choice in demonstrating the thickened pituitary stalk which exibits strong contrast enhancement (Fig.1). In patients with diabetes insipidus the normal high signal of the posterior pituitary gland is not recognizable on T1-weighted images. Intracerebral localizations (Fig.2) appear as tumour-like masses, isointense on T1-weighted and hyperintense on T2-weighted images with grey matter, and display intense contrast enhancement.

The definitive diagnosis is made by biopsy of one of the bone lesions.

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Fig.1

a, b. MR, T1-weighted sagittal (a) and coronal (b) images of a patient with diabetes insipidus. The posterior pituitary hyperintensity is missing. The hypothalamic-chiasmatic region and the proximal stalk are slightly enlarged. c, d. Corresponding MR images following gadolinium injection. Enhancement of the infiltrated pituitary stalk and hypothalamus.
Histiocytosis x, Fig.1 (a)
Histiocytosis x, Fig.1 (b)
Histiocytosis x, Fig.1 (c)
Histiocytosis x, Fig.1 (d)
Histiocytosis x, Fig.2 (a)
Histiocytosis x, Fig.2 (b)