Diffuse cystic lung diseases: differential diagnosis

Abstract

Diffuse cystic lung diseases are characterized by cysts in more than one lung lobe, the cysts originating from various mechanisms, including the expansion of the distal airspaces due to airway obstruction, necrosis of the airway walls, and parenchymal destruction. The progression of these diseases is variable. One essential tool in the evaluation of these diseases is HRCT, because it improves the characterization of pulmonary cysts (including their distribution, size, and length) and the evaluation of the regularity of the cyst wall, as well as the identification of associated pulmonary and extrapulmonary lesions. When combined with clinical and laboratory findings, HRCT is often sufficient for the etiological definition of diffuse lung cysts, avoiding the need for lung biopsy. The differential diagnoses of diffuse cystic lung diseases are myriad, including neoplastic, inflammatory, and infectious etiologies. Pulmonary Langerhans cell histiocytosis, lymphangioleiomyomatosis, lymphocytic interstitial pneumonia, and follicular bronchiolitis are the most common diseases that produce this CT pattern. However, new diseases have been included as potential determinants of this pattern. RESUMO As doenças pulmonares císticas difusas se caracterizam pela presença de cistos envolvendo mais de um lobo pulmonar, que se originam por diversos mecanismos, incluindo dilatação dos espaços aéreos distais por obstrução, necrose das paredes das vias aéreas e destruição do parênquima. Essas doenças apresentam evolução variável. A TCAR é fundamental na avaliação dessas doenças uma vez que permite uma melhor caracterização dos cistos pulmonares, incluindo sua distribuição, tamanho, extensão e regularidade das paredes, assim como a determinação de outras lesões pulmonares e extrapulmonares associadas. Frequentemente a TCAR é suficiente para a definição etiológica dos cistos pulmonares difusos, associada a achados clínicos e laboratoriais, sem a necessidade de realização de biópsia pulmonar. O diagnóstico diferencial das doenças pulmonares císticas difusas é extenso, incluindo etiologias neoplásicas, inflamatórias e infecciosas, sendo as mais frequentes determinantes desse padrão tomográfico a histiocitose pulmonar de células de Langerhans, a linfangioleiomiomatose, a pneumonia intersticial linfocitária e a bronquiolite folicular. Novas etiologias foram incluídas como potenciais determinantes desse padrão.

Figure 1. CT scans of patients with pulmonary Langerhans cell histiocytosis. In A, irregular cysts and irregularly marginated centrilobular nodules in the upper lobes (axial reconstruction). In B, irregular thin-walled cysts (axial reconstruction). In C, irregular cysts predominating in the upper lobes and sparing the region of the costophrenic sinuses (coronal reconstruction). In D, irregular cysts, some centrilobular nodules, and a left pneumothorax (axial reconstruction).

Figure 2. In A, axial reconstruction and, in B, coronal reconstruction of chest CT scans of a female patient with lymphangioleiomyomatosis, showing diffuse lung cysts with regular walls. In C, axial reconstruction of an abdominal CT scan of a female patient with lymphangioleiomyomatosis, showing bilateral, heterogeneous renal masses, consistent with angiomyolipoma. In D, axial reconstruction of a CT scan of a female patient with lymphangioleiomyomatosis, showing diffuse lung cysts and a left chylothorax.

Figure 3. Axial reconstruction of a chest CT scan demonstrating lymphocytic interstitial pneumonia in a female patient with Sjögren's syndrome. Note the areas of ground-glass opacity, the reticular pattern, and the cysts predominating in the lower lung fields.

Figure 4. Axial reconstruction of a CT scan of a female patient with follicular bronchiolitis. Note the thin-walled cysts of various diameters throughout the lung parenchyma, especially along the peribronchovascular bundle.

Figure 5. In A, axial reconstruction of a CT scan demonstrating thin-walled lung cysts and a right pneumothorax. In B, coronal reconstruction of a CT scan showing the distribution of the cysts in the lower lobes, a predominantly medial distribution. The patient in question was a 49-year-old female, had sudden dyspnea, and was diagnosed with Birt-Hogg-Dubé syndrome. The diagnosis was confirmed by the presence of characteristic lung cysts and a spontaneous pneumothorax and by a history of a first-degree relative with the disease.

Figure 6. Chest CT scans. In A, axial reconstruction demonstrating several thin-walled, cystic structures associated with interlobular septal thickening and pulmonary micronodules. In B, coronal reconstruction showing the cranial distribution of the lung cysts. The patient in question was a 38-year-old female and was diagnosed with multiple myeloma, renal failure, and lung involvement associated with light-chain deposition disease.

Figure 7. In A, axial reconstruction of a CT scan demonstrating several thin-walled, cystic structures associated with adjacent nodules, some of which were calcified. In B, coronal reconstruction of a CT scan showing randomly distributed lung cysts and associated nodules. The patient in question was a 56-year-old female and was diagnosed with Sjögren's syndrome and amyloidosis-related lung involvement.

Figure 8. Axial reconstruction of a CT scan of a 66-year-old male patient with laryngeal squamous neoplasia. The scan demonstrates several cavitated nodules with a thick wall and cysts associated with loculated pleural effusion, also etiologically secondary to neoplasia.

Figure 9. CT scans of a 33-year-old male patient who had been HIV-positive for three years and was poorly compliant with treatment. He had dyspnea and lung involvement secondary to pneumocystosis. In A, axial reconstruction demonstrating diffuse areas of ground-glass density, interspersed with bronchial wall thickening and several peribronchiolar cystic structures of various sizes. In B, coronal reconstruction showing lung cysts with a peribronchiolar distribution.

Figure 10. Axial reconstruction of a CT scan of a male patient with a diagnosis of hypersensitivity pneumonitis due to exposure to birds: after the subacute phase, there remained scattered, randomly distributed cysts in the lung parenchyma.

Figure 11. Axial reconstruction of a CT scan of a female patient with limited systemic sclerosis and a desquamative interstitial pneumonitis pattern, which was confirmed by open lung biopsy. The scan shows small-diameter lung cysts interspersed with areas of ground-glass opacity and traction bronchiolectasis, especially in the lower lung fields.