Not always a truly diffuse cystic lung disease – A case of cystic transformation of lung metastases after chemotherapy

A 28-year-old male patient diagnosed with testicular cancer confirmed by histology to be a teratoma mixed with yolk sac and embryonal carcinoma stage IIIB (mediastinal and retroperitoneal lymph node metastases and lung metastases) underwent chemotherapy treatment with bleomycin, etoposide and platinum (BEP), with complete response, followed by annual surveillance with CT.

A chest CT without contrast administration was performed revealing multiple pulmonary cysts with thin wall and diffuse distribution in lung parenchyma without an anterior-posterior distribution predilection, but slightly more prevalent in the inferior portions of both lungs (Figs.1a, 1b and 4b). No solid or subsolid nodules were found nor solid areas were seen within the previously described cystic lesions.

A comparison was made with the patient initial examination revealing multiple pulmonary solid nodules, at the exact same location as the previously described cysts (Figs. 2a, 2b, 3a and 4a).

On the first follow-up CT the referred lung nodules showed central cavitation (Fig. 3b).

Lung cysts are defined as round, air-filled lesions, thin-walled with a diameter greater than 1cm.

Diffuse cystic lung diseases (DCLD) are a group of pathologies characterised by the presence of cysts in both lungs that are not necessarily equally distributed. The differential diagnosis is limited and typically includes lymphangioleiomyomatosis (LAM), pulmonary Langerhans cell histiocytosis (PLCH) and lymphoid interstitial pneumonia (LIP). However in a subset of oncologic disease cystic pulmonary metastases, although rare, should always be considered [1–3].

Cavitary lung lesions are relatively common regarding the spectrum of metastatic tumours, cystic lung metastases however are rare and distinct, as the former are characterised by thickened and irregular walls due to central necrosis [1,4]. Metastatic cystic lung lesions have been reported secondary to different types of tumours as seminoma, Ewing’s sarcoma, myxosarcoma, Wilms’ tumour, osteogenic sarcoma, angiosarcoma, transitional cell carcinoma and teratocarcinoma [2].

LAM is rare and usually seen in women of childbearing age. It is usually associated with tuberous sclerosis, therefore concomitant angiomyolipomas are frequently seen. Characteristic high-resolution CT (HRCT) features are diffuse thin-walled round cysts measuring 2-10mm, surrounded by normal lung without regional sparing [3].

LIP usually occurs in association with connective tissue diseases. On HRCT it is characterised by the presence of basal predominant thin-walled cysts, however generally it is also associated with ground-glass opacities and poorly defined centrilobular nodules [5].

PLCH is a smoke-related disease usually presenting from 20 to 40 years. The initial HRCT findings of PLCH are centrilobular or peribronchiolar nodules. As the disease progresses, the nodules undergo cavitation and produce cystic lesions, which would be a consideration on the case presented if a history of oncologic imaging was not present [5].

HRCT has become the gold standard in the evaluation of patients with DLCD, since the analysis of the characteristics and distribution of the cysts, as well as the clinical history, makes it possible to reach a definitive diagnosis or to narrow the differential diagnoses.

In the case presented and in all oncologic patients we should always have into account the previous studies as they might be the key for diagnosis. In this case, the previously known lung metastatic disease that was submitted to adjuvant therapy allowed the diagnosis. However, in cases where a previous study is not available, metastatic lung disease although rare, should always be considered as a cause of diffuse cystic lung disease, especially in the subset of chemotherapy treated patients.

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