Ultra-rare cystic disease

Abstract

Diffuse cystic lung diseases include a group of heterogeneous disorders characterised by the presence of cysts within the lung parenchyma, sometimes showing a characteristic computed tomography scan pattern that allows diagnosis. The pathogenetic mechanisms underlying cyst formation in the lung are still not clear and a number of hypotheses have been postulated according to the different aetiologies: ball-valve effect, ischaemic dilatation of small airways and alveoli related to infiltration and obstruction of small vessels and capillaries that supply the terminal bronchioles and connective tissue degradation by matrix metalloproteases. A wide number of lung cyst diseases have been classified into six diagnostic groups according to the aetiology: neoplastic, congenital/genetic, lymphoproliferative, infective, associated with interstitial lung diseases, and other causes. This article focuses on lymphangioleiomyomatosis, pulmonary Langerhans cell histiocytosis and Erdheim-Chester disease, Birt-Hogg-Dubé, follicular bronchiolitis and lymphocytic interstitial pneumonia, light-chain deposition disease and amyloidosis, congenital lung disease associated with aberrant lung development and growth, and cystic lung disease associated with neoplastic lesion. These cystic diseases are epidemiologically considered as ultra-rare conditions as they affect fewer than one individual per 50 000 or fewer than 20 individuals per million. Despite the rarity of this group of disorders, the increasing use of high-resolution computed tomography has improved the diagnostic yield, even in asymptomatic patients allowing prompt and correct therapy and management without the need for a biopsy.

FIGURE 1

a) High-resolution computed tomography scan of the chest in a patient with lymphangioleiomyomatosis (LAM). Round, thin-walled round cysts are distributed diffusely throughout the lungs. The patient underwent right pleurodesis for pneumothorax. b) Surgical lung biopsy showing several thin-walled cysts of varying dimensions with small plaques of LAM cells in the wall of the cysts (arrows) (Haematoxylin and Eosin stain, 20×). Figure was provided courtesy of A. Cavazza (Unit of Pathologic Anathomy, Azienda Arcispedale S, Maria Nuova/IRCSS, Reggio Emilia, Italy).

FIGURE 2

High-resolution computed tomography scans of the chest in a patient with pulmonary Langerhans cell histiocytosis with a combination of small nodules, cavitary nodules and lung cyst in a) the upper lobe and b) lower/angle costophrenic sparing.

FIGURE 3

High-resolution computed tomography scans of the chest in a patient with Birt–Hogg–Dubé. Round and lenticular shaped thin-walled cysts with a prevalent lower and subpleural distribution can be seen in a) the upper lobes and b) lower lobes.

FIGURE 4

Surgical lung biopsy of a patient with Birt–Hogg–Dubé showing large thin-wall lung cysts surrounded by normal lung parenchyma with no evidence of lymphangioleiomyomatosis cells or signs of inflammation or tumour (Haematoxylin and Eosin, 20×). Figure was provided courtesy of A. Cavazza.

FIGURE 5

Forehead fibrofolliculoma in a patient with Birt–Hogg–Dubé.