What is the abnormality?
What is its distribution?
What is the relation of the vessels to the abnormality?
Case 27
Section 1
Look at images 1 and 2.
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What is the abnormality?
What is its distribution?
What is the relation of the vessels to the abnormality?
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Image 2
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Section 2
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Gross Appearance This slice of left lung shows the size and distribution of cysts. The cyst walls are uniformly thin. The subpleural location of some cysts accounts for the predisposition to pneumothorax. The texture on palpation is normal, in contrast to emphysema, which is softer than normal. It is not firmer than normal as in fibrosis and honeycombing. Also in contrast to emphysema, in which the alveolar walls collapse when fixative escapes, the cyst walls remain upright. |
Section 3
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Histologic Findings This proliferation of smooth muscle around a small vein (V) causes focal venous obstruction. Lymphatics may also be narrowed by the muscle proliferation. These nodular proliferations are below the resolution of HRCT. In contrast to normal smooth muscle in the lung, this muscle reacts with an antibody to a melanoma-associated antigen, HMB-45. Find the small vein. | ||||||
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Cystic Change Here, perilymphatic nodules of smooth muscle appear to float in cystic spaces. An intact airway is also present. The interstitium and air spaces frequently contain hemosiderin-laden macrophages, possibly resulting from tearing of small vessels by air trapped in the cysts. Find 2 nodules of smooth muscle. Find a bronchiole. | ||||||||||
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Subpleural Cyst A subpleural cystic space is surrounded by alveoli. There is no fibrous wall to the cyst. Note the RBCs in the lumen. Find the cystic space. | ||||||||||
Differential diagnosis of multiple lung cysts on HRCT: Lymphangioleiomyomatosis, emphysema (cysts and walls usually less well-defined), chronic interstitial lung diseases (honeycombed cysts usually peripheral), Langerhans' cell histiocytosis (nodules ± cavities, presence of thicker-walled cysts, upper lung predominance), bronchiectasis (tree-and-bud pattern often present), sarcoidosis (cysts usually apical), and pneumatoceles (commonly seen with pneumocystis pneumonia)
Histologic differential diagnosis: Lymphangioleiomyomatosis; emphysema (if smooth muscle nodules not recognized); smooth muscle proliferations such as "benign" metastasizing leiomyoma, metastatic stromal sarcoma of the uterus, and metaplastic muscle bundles in fibrosing lung diseases; and alveolar hemorrhage syndromes (if hemosiderin deposits frequent)
Diagnosis: Lymphangioleiomyomatosis
Diagnostic features of lymphangioleiomyomatosis on HRCT
Comment: HRCT is required for diagnosis of lymphangioleiomyomatosis. Progression of disease may be related to two factors: activation of matrix metalloproteinases in the proliferating cells and air-trapping [1]. Trapped air can dissect into edematous lymphatics and cause interstitial emphysema.
Reference
1. Matsui K, Takeda K, Yu Z, Travis W, Moss J, Ferrans V. Role for activation of matrix metalloproteinases in the pathogenesis of pulmonary lymphangioleiomyomatosis. Arch Pathol Lab Med 2000; 124:267-275.
Numerous thin-walled, rounded cysts of varying size. Intervening lung is mostly normal without nodularity or architectural distortion. Note that the cyst contents are as dark as the air in the tracheobronchial tree.
Cysts are distributed evenly throughout the lungs in upper, as well as lower, lung zones.
Vessels frequently lie adjacent to, or along, the cyst wall.
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