LAM from a few to almost complete replacement of normal lung tissue. The profusion of cysts tends to be milder in patients with TSC-LAM than S-LAM, perhaps explained in part because TSC-LAM patients typically receive earlier screening. Pleural effusions are seen on CT in 12% of patients with S-LAM and 6% of patients with TSC-LAM. Other CT features include linear densities (29%), hilar or mediastinal lymphadenopathy (9%), pneumothorax, lymphangiomyoma, and thoracic duct dilation. Ground-glass opacities (12%) suggest the presence of interstitial edema due to lymphatic congestion. In patients with TSC, nodular densities on HRCT may represent multifocal micronodular pneumocyte hyperplasia (MMPH) made up of clusters of hyperplastic type II pneumocytes. MMPH may be present in males or females with TSC in the presence or absence of LAM, but not in patients with S-LAM. MMPH is not typically associated with physiologic or prognostic consequences, but one case of respiratory failure due to MMPH has been reported. Ventilation-perfusion scans In one study ventilation-perfusion scans were abnormal in 34 of 35 LAM patients. The most common abnormality was nonspecific diffuse heterogeneity, usually grossly matched. These authors also described an “unusual,” “speckling pattern” on the perfusion images in 74% of patients, consisting of “small, often peripheral collections of radioisotope.” Positron emission tomography LAM and AML lesions do not typically exhibit increased uptake of 18F-fluorodeoxyglucose on positron emission tomography (PET) scanning. Other neoplasms (or sources of inflammation) should therefore be considered in known or suspected LAM cases in which FDG-PET results are positive. Abdominal imaging Abnormalities on abdominal imaging, such as renal AML and enlarged lymphatic structures, are also common in LAM. Fat density within a renal mass is pathognomonic of AMLs. AMLs are more prevalent and more frequently bilateral and large in patients with TSC-LAM than in patients with S-LAM. AML size correlates with the prevalence of pulmonary cysts in patients with TSC. One study CT imaged 256 patients with S-LAM and 67 with TSC-LAM. Renal AMLs were present in 32% of patients with S-LAM and 93% of patients with TSC-LAM. Hepatic AMLs were present in 2% of patients with S-LAM and 33% of patients with TSC-LAM. Ascites was uncommon, seen in fewer than 10% of patients with LAM. Abdominal lymphangiomatosis, often containing both cystic and solid components, were seen in 29% of patients with S-LAM and 9% of patients with TSC-LAM. Central nervous system imaging Central nervous system abnormalities, such as cortical or