The Langerhans cell histiocytoses (also referred to as Histiocytosis X) represent clonal proliferations of these antigen presenting dendritic cells, which are normally found in many organs. Image
The histologic appearance of eosinophilic granuloma in the lung is comparable to that elsewhere, notably in bone.
In early stage of the lesion, there is a nodular infiltrate at the center and the periphery of the acinus.
It is the latter situation at the pleura that leads to pneumothorax.
The lesions excavate and discharge their content into the airways, and the X cells may then be recognized in the sputum.
Healing by scarring results in the formation of large cysts.
Eosinophilic granuloma of the lung is primarily a disease of young adults and usually presents as dyspnea.
About 20% of patients have spontaneous pneumothorax in the course of the disease.
Radiologically,it differs from other forms of infiltrative lung disease in that it is mainly upper zonal and large cystic spaces may be apparent.
It was the first condition described under the heading "honeycomb lung".
In most cases, the lesion is limited to the lung, but in some the disease may affect bones (usually the ribs) or may be disseminated.
When the base of the skull is affected, particularly the orbit (with proptosis) and pituitary (with diabetes insipidus), eosinophilic granuloma of the lung is regarded as a complication of the Hand-Schüller-Christian disease triad.
Involvement of the lung in cases of disseminated eosinophilic granuloma is thought to represent a complication of Letterer Siwe disease, although many of the cases are probably lymphomas.
Because of the heterogeneity of presentations, despite the similarity of the histologic appearance, the conditions are often collectively referred to as histiocytosis X, and the abnormal Langerhans cells are referred to as X cells.
The tumour cells have abundant, eosinophilic, often vacuolated cytoplasm, and the cell margins are well defined.
The nuclei are large with open chromatin, and often notched.
When cut longitudinally, the notch appears as a central bar through the nucleus.
Varying numbers of eosinophils are present in the nodular lesion.
The combination of histiocytes and eosinophils gives the condition its name.
Under the electron microscope cytoplasmic structures known as HX bodies (Birbeck granules) are seen, which sometimes have a periodicity and a dilated terminal end that produces an appearance resembling a tennis racquets or even an octopus complete with tentacles.
Similar cells are occasionally encountered in the bronchiolar epithelium of the normal lung and in about one third of all cases of usual interstitial pneumonia and its variants.
However, in eosinophilic granuloma the cells are more profuse.
A prominent infiltrate of reactive cells, including plasma cells, macrophages, and eosinophils (which may be scant or numerous), is usually mixed with the neoplastic histiocytes.
The differential diagnosis is with sarcoidosis , usual interstitial pneumonia and its variants, diffuse metastases, lymphoma and eosinophilic pneumonia.
The prognosis of eosinophilic granuloma of lung is controversial.
When it is limited to the lung and diagnosed by biopsy,some 80% of all cases remain the same or improve.
15% gradually get worse, and 5% die of respiratory failure.
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