LAM is lymphangiomyomatosis. This fascinating but rare tumor occupies a place in favorite test questions for medical students who are presented with a young woman with a history of repeated pneumothorax. In addition to pneumothorax, there may be shortness of breath, cough, hemoptysis, and chylous pleural effusions.
The importance of this diagnosis lies with its close association with tuberous sclerosis. Indeed, in fully expressed cases of tuberous sclerosis, tumors having histologically similar appearances in the kidney (angiomyolipomas), abdominal or thoracic lymphatic ducts, and lymph nodes may occur. This has led some to speculate that LAM is a limited or forme fruste expression of tuberous sclerosis.
Under the microscope, there is a lacy proliferation of smooth muscle bundles within the interstitial spaces, extending around bronchi, bronchioles, and blood vessels. The smooth muscle cells may have an optically clear cytoplasm filled with glycogen. Bronchiolar obstruction by the smooth muscle may lead to air trapping and overdistension leading to cystic blebs and pneumothorax. Obstruction of the veins and lymphatic flow may lead to hemorrhage and lymphatic cysts which may rupture causing chylous effusions. An interesting characteristic of the smooth muscle is the immunopositivity for HMB-45 and estrogen and progesterone receptors. Some patients have multifocal proliferations of alveolar type II pneumocytes called micronodular pneumocyte hyperplasia. These proliferations are negative for HMB-45 and hormone receptors.
The pathologist must distinguish this disorder from benign metastasizing leiomyomas which are localized smooth muscle proliferations and not diffuse. Metastatic endometrial stromal sarcomas to the lung may be cystic and must be distinguished. Diffuse pulmonary lymphangiomatosis are seen in all ages and sexes. There are prominent lymphatic vessels in the pleura and connective tissue septa with smooth muscle proliferation. Unlike LAM, there are no cysts, pneumothorax, or HMB-45 positivity. Chylothorax may occur.
GROSS APPEARANCE/CLINICAL VARIANTS CHARACTERIZATION General VARIANTS Extrapulmonary disease
Hum Pathol 2000;31:1242-1248
Affected lymph nodes of the mediastinum and retroperitoneum
Occurred in 22 women
Sternberg S. Diagnostic Surgical Pathology. Third Edition. Lipincott Williams and Wilkins 1999.
Hemoptysis-Coughing up blood.
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