Miliary pulmonary metastases from mesothelioma (miliary mesothelioma)

Clinical History

A 60-year-old patient on palliative chemotherapy for known pleural mesothelioma presented with a 3-week history of progressive shortness of breath and generalized deterioration. There were no signs of any concurrent second malignancy or any infection.

Imaging Findings

The initial chest radiograph (figure 1a) and CT examination (figure 2a) performed 6 months prior to the current admission demonstrate circumferential pleural thickening with volume loss affecting the left hemithorax with imaging features typical for pleural mesothelioma. At this stage there was no evidence of chest wall or diaphragmatic invasion or contralateral lung involvement. During the admission, the chest radiograph (figure 1b) showed deterioration of pleural thickening and accompanying volume loss of the left hemithorax. In addition there was a suggestion of numerous miliary type nodules throughout the contralateral (right) lung. These findings were further confirmed by a CT scan (figure 2b). The patient continued to deteriorate clinically and a subsequent CT scan 2 weeks later (figure 2c) demonstrated even worse pleural thickening, volume loss and interlobular septal thickening of the left hemithorax with many more conspicuous miliary type nodules within the right lung.

Discussion

Mesothelioma is a neoplasm that generally carries a very poor prognosis. It typically arises from serosal membranes of the pleura and rarely from the pericardium and/or peritoneum [1]. Its typical pattern of growth is by aggressive local spread [1-2], with tumour frequently invading the chest wall, mediastinum, and / or diaphragm. Tumoural encasement with retraction of the lung (as was shown even on the initial images of the presented case) is a typical imaging feature [1]. In autopsy studies, 40-45 % of cases may have metastatic hilar or mediastinal nodal involvement.

A much rarer metastatic pattern of mesothelioma is the one characterized by distant ipsilateral or contralateral lung metastases. This tends to occur particularly in the late phase of disease [3].
Contralateral pulmonary metastases can manifest in various forms which include:

1. Large masses [1]
2. Smaller nodular lesions [1]
3. Alveolar opacities [4]
4. Small miliary lesions [5-6]

It is thought that the incidence of distant ipsilateral or contralateral lung metastases have become more common over the recent years in the advent of more modern treatment strategies (i.e. induction chemotherapy followed by extra-pleural pneumonectomy and adjuvant high-dose hemithoracic radiation therapy) especially as patients live longer with the disease giving more opportunity for the disease to manifest in more atypical forms [2].

A miliary metastatic pattern to the lungs is still an uncommon phenomenon overall [1, 3-7]. This can involve both the ipsilateral as well as contralateral lung [8]. Important differential diagnoses to consider on imaging include miliary type nodules secondary to a concurrent infective source (haematogenous infection or miliary tuberculosis) or miliary metastases from a concurrent second malignancy. This case highlights the imaging features of an uncommon but recognised mode of disease spread of mesothelioma as miliary lung metastases.

Differential Diagnosis List

Final Diagnosis

Miliary metastases from mesothelioma

URL:	https://www.eurorad.org/case/10569
DOI:	10.1594/EURORAD/CASE.10569
ISSN:	1563-4086