Lymphangioleiomyomatosis (LAM) is a rare idiopathic disease affecting women that was first described by von Stossel in 1937. LAM is characterized by nonneoplastic peribronchial, perivascular, and perilymphatic proliferation of atypical smooth muscle resulting in vascular and airway obstruction, cyst formation, and a progressive decline in lung function. In the 2015 WHO classification,  LAM was classified as one of three forms of PEComataous tumor (arising from perivascular epithelioid cells), along with benign PEComas (including clear cell tumor), and malignant PEComas. Although historically LAM has been considered an interstitial lung disease, it is now considered to be a low-grade destructive metastasizing neoplasm. Typical radiographic findings of reticular interstitial lung disease, recurrent pneumothoraces, and recurrent chylous effusions have been described. [2, 3, 4, 5, 6] (See the image below.)
An association with renal angiomyolipomas is observed in as many as 50% of patients. The disease may occur sporadically or as part of the tuberous sclerosis complex (TSC) that includes mental retardation, seizures, and skin abnormalities.  However, less than 5% of patients with TSC have pulmonary disease. When pulmonary features of LAM are identified in males, consider a diagnosis of TSC. Angiomyolipomas are seen in the images below. [3, 7, 8, 9]
With clinical suspicion, lymphangioleiomyomatosis (LAM) has been diagnosed on the basis of compatible chest radiograph, pulmonary function tests (PFTs), and computed tomography (CT) scan findings. CT scanning is the most specific imaging test for diagnosing LAM. [10, 11, 12]
Limitations of techniques
Chest radiograph and pulmonary function test (PFT) findings, while suggestive of lymphangioleiomyomatosis (LAM), can be nonspecific and may be normal despite the presence of symptoms. Plain radiography may not detect the thin-walled cysts identified on CT and may underestimate the extent of the disease. PFT results vary depending on the extent of disease. CT scanning, and especially high-resolution CT (HRCT) scanning, may reveal distinct findings that obviate the need for biopsy; however, diseases such as emphysema occasionally must be excluded. CT detection of a renal angiomyolipoma or chylous ascites further supports the diagnosis.
Initial film is abnormal in more than 95% of patients with LAM.
A symmetrical, diffuse, reticular interstitial pattern (shown in the image below), caused by summation of multiple cyst walls, is typical.
If Kerley B lines are present, they may be the result of interstitial edema related to lymphatic obstruction. Multiple cysts become visible as they enlarge. Occasionally, patients may present with pneumothorax or chylous pleural effusion.
LAM is one of the few interstitial diseases in which lung volumes are maintained or increased. Cystic fibrosis and Langerhans cell histiocytosis (eosinophilic granuloma) share this feature.
A high index of clinical suspicion for lymphangioleiomyomatosis (LAM) should be maintained in women of childbearing age who present with recurrent pneumothoraces, when chylous effusion or an interstitial pattern on chest radiograph is not identified.
Large lung volumes and interstitial disease on plain film also can be seen with Langerhans cell histiocytosis, sarcoidosis, and extrinsic allergic alveolitis. Occasionally, emphysema presents with a similar pattern as a result of summation of widespread small bullae.
Initial CT scan findings are almost always abnormal despite a normal chest radiograph.
The typical appearance of LAM on HRCT is of thin-walled, air-containing cysts ranging from 2-50 mm in a diffuse symmetric pattern. The cyst walls range from 2 mm to an almost imperceptible thickness, and the cysts usually are round, but they may be polygonal. Intervening lung tissue appears normal. LAM cysts are shown on the image below.
CT scanning also may reveal lymphadenopathy, small pneumothoraces, alveolar hemorrhages, and septal lines. Ground-glass opacity, if seen, may result from hemosiderosis or proliferation of smooth muscle.
CT scan of the abdomen may detect lymphadenopathy or renal angiomyolipoma. The kidneys should be included in the initial imaging if LAM or tuberous sclerosis complex (TSC) is suggested.
In Langerhans cell histiocytosis and in neurofibromatosis, cysts are seen predominantly in the upper lung zones. In addition, most patients with Langerhans cell histiocytosis have small pulmonary nodules initially, and cyst walls are not entirely uniform.
Magnetic Resonance Imaging
A single case report of lymphangioleiomyomatosis (LAM) describes the appearance of thin-walled cysts on spin-echo of the lung.
Ultrasonography has not been proven useful for the diagnosis of LAM or of any other interstitial lung disease. An angiomyolipoma is seen in the ultrasonogram below. 
In most patients with LAM, aerosol ventilation-perfusion scintigraphy reveals a speckled pattern of uptake on ventilation images. This appears distinct from the central clumping seen with poor aerosolization. The speckled pattern is believed to result from focal areas of activity on cyst walls by adherent aerosolized particles. The extent of the speckling seems to correlate to disease extent as determined by chest radiographs, PFTs, and CT scans. 
Degree of confidence
Specificity is unknown, although it is possible that a severe pattern of speckling is specific for LAM. Other lung diseases that produce cysts also may produce a speckled pattern.