Monday, January 21, 2019 | 18:00 CET
Cystic changes of the lungs
Anastasia Oikonomou, Toronto/CA

Description
True cysts are commonly seen on chest CT as an isolated finding or in combination with nodules, ground glass opacity or consolidation and differential diagnosis can be challenging.
Diseases presenting with decreased attenuation such as emphysema, obliterative bronchiolitis, cystic bronchiectasis and cystic metastases may also mimic cystic disease.
Pulmonary Langerhans cell histiocytosis (PLCH) is a rare type of histiocytosis occurring in smokers, characterized by infiltration of tissues with dendritic Langerhans cells. PLCH may exclusively involve lungs or rarely be part of multisystem disease. HRCT findings include nodules, combination of nodules and cysts or only cysts with upper lobe distribution and sparing of lung bases. Coexistence of cysts with GGO is common. Cysts are bizarre-shaped, thin or thick-walled and variable in number and size. Nodules with or without cavitation have a centrilobular location. Pneumothorax may be the initial manifestation.
Lymphangioleiomyomatosis (LAM) is a rare cystic lung disease caused by infiltration of the lungs with smooth muscle cells. It occurs in patients with tuberous sclerosis (TSC-LAM) and in a “sporadic” form (S-LAM), exclusively seen in women of reproductive age.
Parenchymal lesions in LAM mainly include cysts, which are thin-walled, well-defined, rounded, may reach large numbers and have no zonal predominance. Nodules are extremely rare in S-LAM and may be seen in TSC-LAM. They represent multifocal micronodular pneumocyte hyperplasia. Chylothorax and pneumothorax are common.
When both cysts and nodules coexist then PLCH should be differentiated from LIP, amyloidosis or light-chain disease. When only nodules or only cysts are present then differential diagnosis includes nodular diseases (only for PLCH) such as sarcoidosis, silicosis, tubercusolis, amyloidosis and metastases or cystic lung diseases (both for PLCH and LAM) such as LAM and PLCH respectively, Birt-Hogg-Dubbe, lymphocytic interstitial pneumonia (LIP) and amyloidosis. If cysts coexist with GGO then PLCH is differentiated from pneumocystis pneumonia, desquamative interstitial pneumonia and LIP.
Integration of imaging features with clinical and laboratory findings may help differentiate among various cystic lung diseases and mimics, allowing accurate diagnosis.

Learning objectives
1. To learn about the typical radiological features of the most common cystic lung diseases
2. To discuss the findings of the most common mimics of cystic lung disease
3. To discuss the possible overlap amongst common cystic lung changes or with other non-cystic lung changes
4. To appreciate the clinical relevance of recognizing and differentiating these entities