Lymphangioleiomyomatosis (LAM) is a disease characterised histologically by two key features: cysts and proliferation of atypical smooth muscle cells (LAM cells) of the pulmonary interstitium, particularly in the bronchioles, pulmonary vessels and lymphatics. LAM is a rare disease seen almost exclusively in women, the vast majority of cases being diagnosed during childbearing age. However, there are reports of women developing LAM after the menopause, including women in their eighth decade. LAM can occur with or without evidence of other disease, such as tuberous sclerosis complex.
The most commonly described radiographic manifestation of LAM is a pattern of generalised, symmetrical, reticular, or reticulonodular opacities with normal or increased lung volumes. Pleural effusions (chylous) occur in 10–40% of patients (these may be unilateral or bilateral) and pneumothoraces in approximately 50% of cases. The CT manifestations of LAM are distinctive, characterised by numerous thin-walled cysts randomly distributed throughout the lungs with no zonal predilection (Fig. 1). Imaging features that help distinguish LAM from LCH include a more diffuse distribution of cysts, typically with no sparing of the bases, more regularly shaped spherical cysts and normal intervening lung parenchyma. Occasionally HRCT may demonstrate interlobular septal thickening (attributed to dilatation of lymphatic channels secondary to obstruction of pleuropulmonary lymphatics and/or septal veins) or patchy areas of ground-glass attenuation (presumably the result of pulmonary haemorrhage).
Classic HRCT Findings
• Diffuse thin-walled cysts throughout the lungs with no zonal predominance
FIGURE 1 ■ Lymphangioleiomyomatosis. (A) There is a profusion of thin-walled cystic air spaces scattered evenly throughout the lungs. The cysts are relatively uniform in size. (B) In a more advanced case of LAM, note the small left pleural effusion.
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