Langerhans' cell histiocytosis

(Paul Langerhans, 1847-1888, German pathologist), this is a group of disorders involving histiocytic proliferation with Langerhans' cells in the cytoplasm of these cells, with a clinical course ranging from benign to aggressive. There are several classifications. Originally described as three conditions, benign eosinophilic granuloma, Hand Schuller Christian disease, and the more systemic involvement of Letterer Siwe disease. The condition is now termed Langerhans' cell histiocytosis, and is classified on a histological basis:

class 1 Langerhans' histiocytosis;

class 2 histiocytosis (derived from mononuclear cells other than Langerhans' cells); and

class 3 malignant histiocytic disorders. The condition is now termed Langerhans' cell histiocytosis.

Presentation of the benign form is as solitary or multiple bone lesions, particularly of the skull and long bones, presenting with pain or a mass. Other flat bones, particularly the pelvis and the femur may also be involved. Soft tissue involvement without bony involvement also occurs. Orbital infiltration presents with exophthalmos and mandibular lesions - loosening of the teeth, causing a floating teeth appearance. Petrous bone infiltration may lead to discharge from the ear (Fig.1). Pulmonary involvement produces cough and dyspnoea (Fig.2). Thymic involvement presents as an anterior mediastinal mass which may contain calcification. Disseminated Langerhans' cell histiocytosis, Letterer Siwe disease, presents as fever or failure to thrive. Lung, liver and bone involvement is associated with high mortality, and is seen particularly in the younger age group. Hepatosplenomegaly, which may be confirmed by ultrasound, occurs sometimes with ascites. Splenomegaly is usually associated with bone marrow involvement or is enlarged due to infiltration by Langerhans' cells secondary to portal hypertension in liver disease. Solitary bone lesion or single system involvement occurs in general in older children. Diabetes insipidus may occur owing to involvement of the pituitary gland. Involvement of the cranial vault may rarely present as dysarthria and nystagmus due to extension to the cerebellum.

If the lungs are involved the radiographs will initially show widespread reticulonodular change and later a honeycomb pattern due to fibrosis and bullae. A mediastinal mass, due to thymic involvement, may covertly be the initial presentation. The mass often contains calcification. These usually occur in the younger age group. The older child usually presents with skeletal involvement in the skull or long bones (Fig.3) (Fig.4). This will show as a lucency in the skull vault with a clearcut margin, often in the so-called geographical distribution. There is usually some soft tissue swelling. Occasionally a sequestrum is seen as a density centrally. In addition to vault lesions there may be involvement of the supraorbital margin and mastoids. Mandibular lesions produce so-called floating teeth with a lytic area surrounding the teeth. In bony lesions there may be central permeative rarefaction with prominent periosteal new bone, which may often be mistaken for chronic infection. In the spine there may be collapse in the vertebral bodies. If focal, it may produce 'vertebra plana' with a plate-like appearance  eosinophilic granuloma (Fig.5).

MRI shows the pituitary involvement in patients with diabetes insipidus. CT is rarely needed although can show the bone destruction to better advantage if it is unclear on MRI. If CT is done it shows the vault lesions to have bevelled edges, sometimes with a central sequestration. The soft tissue lesions have low signal on T1-weighted images, with high signal on T2 and STIR sequences. There is enhancement with intravenous contrast medium on both CT and MRI. In spinal lesions there may be intraspinal extension and cord compression. Skeletal survey and bone scintigraphy show the extent of disease. Bone scintigraphy shows activity if there is destruction of bone but if the disease is in a quiescent phase, it may be negative even though the bone seen on the radiograph shows abnormality. Skeletal radiographs may be negative at sites positive on the bone scan if the lesion is very early in its evolution.

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