Pulmonary interstitial gas surrounding lung metastases

Clinical History

A 25-year-old patient with stage IV metastatic testicular germ cell cancer, Tx N2 M1; including pulmonary metastases, developed progressive respiratory compromise during intensive induction chemotherapy. On minimal exertion he desaturated to oxygen saturations of 70%. CTPA was negative for pulmonary emboli and bronchoalveolar lavage specimens were negative for atypical infections.

Imaging Findings

CT thorax at initial deterioration demonstrated inflammatory interstitial thickening of the lower lobes bilaterally and right upper and middle lobes. Nine days later repeat CT showed progressive pulmonary appearances with significant progression of patchy ground-glass opacification, cavitation of a right upper lobe mass and formation of pulmonary interstitial emphysema (PIE) and extensive pneumomediastinum extending to the neck. Low attenuating gas-filled cysts surrounding pulmonary lesions, a small left apical pneumothorax and pretracheal adenopathy were also seen.

Despite a change in chemotherapy regimen repeat plasma beta-hCG levels rose indicative of tumour progression. Unfortunately he deteriorated further with worsening hypoxia – requiring intensive care admission. Ventilation was considered inappropriate due to his lung architecture. There were no further treatment options and palliative measures were commenced - he died 24 hours later.

Discussion

Background & Clinical Perspective:

Testicular tumours are the most common solid malignant tumour in men aged between 20 and 39 years [1.] The overall prognosis is excellent when compared to other cancers; dependent on tumour histology and stage and largely attributable to effective chemotherapy. Germ cell tumours account for over 90% of testicular cancers and are split evenly between seminomas and non-seminomatous germ cell tumours (NSGCTs). NSGCTs contain embryonal stem cells and can be classified into: embryonal, teratoma, choriocarcinoma, yolk sac tumour or mixed. [2]

This patient had choriocarcinoma subtype with extensive lung and liver metastases (stage III) and considered of poor prognosis; therefore, with 48% chance of 5-year survival with chemotherapy. Stage III patients are stratified into good, intermediate or poor prognosis: with their overall 5-year survival with primary chemotherapy treatment, 92%, 80% and 48% respectively. [3]

Pulmonary Interstitial Emphysema (PIE) is a rare condition whereby air dissects within the pulmonary interstitium: typically in the peribronchovascular sheaths, interlobular septa, and visceral pleura, as a result of alveolar and terminal bronchiolar rupture. It results in the formation of cystic structures with an associated inflammatory reaction. PIE leads to compression of adjacent functional lung tissue and vascular structures - hindering both ventilation and pulmonary circulation. It is typically seen in neonates receiving ventilatory support but has been observed very rarely in adults, usually associated with mechanical ventilation. In other cases, the cause could be air trapping from mechanical obstruction, necrotizing pneumonia, decreased lung compliance or mechanical trauma. Interstitial air may resolve spontaneously or progress with decompression into adjacent spaces causing pneumomediastinum, pneumothorax, pneumopericardium, pneumoperitoneum or subcutaneous emphysema which if large enough can be life-threatening. [4, 5] Therefore the early detection of PIE, particularly in ventilated patients, and subsequent management could reduce progression to severe barotrauma.

Imaging Perspective:

Early features of PIE can be subtle but include the characteristic lucent halo. Chest X-ray findings include parenchymal and subpleural cysts, perivascular halos, intraseptal air, and linear lucencies extending to the mediastinum. CT findings are more readily identifiable and include air tracking along the bronchovascular sheaths, parenchymal stippling, and cysts. [6, 7] PIE has previously been reported in a patient with metastatic choriocarcinoma under chemotherapy. [8]

The appearance of thin-walled cavities arising at the sites of pulmonary metastases from germ cell tumours treated with chemotherapy has previously been described and termed ‘pulmonary lacunae’. They occur with a prevalence of approximately 7% in patients with multiple pulmonary metastases from testicular teratoma. [9]

Differential Diagnosis List

Final Diagnosis

Progressive NSGCT, extensive pulmonary interstitial emphysema and pulmonary lacunae.

URL:	https://www.eurorad.org/case/13387
DOI:	10.1594/EURORAD/CASE.13387
ISSN:	1563-4086