Micronodular metastases of melanoma mimicking granulomatous disease

Dear Editor, A 62-year-old man arrived at the emergency room complaining of a dry cough, significant deterioration of his general condition, and mental confusion. Laboratory test results were normal. A chest X-ray was unremarkable. Chest CT showed small nodules scattered throughout the lungs, suggesting granulomatous disease [Figure 1]. The patient was sent to a referral hospital for diagnostic investigation. Physical examination revealed purplish and blackened skin lesions. Serological test results were negative. Bronchoalveolar lavage yielded negative results for fungi, mycobacteria, and neoplastic cells. A review of the CT scan by a thoracic radiologist highlighted the presence of several larger nodules and nodular thickening along the interlobular septa and fissures, suggestive of micronodular metastases. In addition, several subcutaneous nodules were observed in the thoracic and abdominal walls, as well as hypodense lesions in the liver, consistent with metastases [Figure 2]. Biopsy of a skin lesion led to the diagnosis of melanoma. The patient died 2 weeks after admission, with a final diagnosis of metastatic dissemination of melanoma.Figure 1: Chest CT images with axial (a and b), coronal (c), and sagittal (d) reconstruction show small and some larger (arrowheads) nodules disseminated throughout the lungs. Note also the small nodules along the fissures (arrows) and interlobular septa, characterizing lymphatic involvement. (e and f) Axial maximum-intensity projections demonstrate diffuse micronodular lesions with the random distribution, indicating hematogenous disease disseminationFigure 2: (a and b) Multiple nodular melanoma metastases on the face and anterior chest wall (arrows). (c and d) Axial slices of the thoracoabdominal transition with windows to the mediastinum showing subcutaneous nodules (arrows) and hypodense lesions in the liver (arrowheads), consistent with metastasesMicronodular lung disease is defined by the presence of diffuse pulmonary nodules < 3 mm in diameter. Nodular distribution throughout the lung parenchyma can be categorized as centrilobular, perilymphatic, or random. Centrilobular nodules may be found in cases of hypersensitivity pneumonitis, silicosis, and infectious bronchiolitis. Perilymphatic nodules are commonly found in cases of sarcoidosis, silicosis, and lymphangitic carcinomatosis. Randomly distributed nodules are generally related to hematogenous dissemination, including metastasis and miliary granulomatous diseases, particularly tuberculosis and histoplasmosis.[1,2] Hematogenous dissemination is the most common form of metastasis to the lungs. Lung metastases have several forms of radiological presentation, depending on the primary tumour type. Miliary nodules form an uncommon pattern of hematogenous lung metastasis characterized by the diffuse, random distribution of innumerable small nodules.[1-3] This pattern can be seen with highly vascular primary tumours, such as those of melanoma, thyroid cancer, breast cancer, ovarian cancer, and renal cell carcinoma, among others, and may be misdiagnosed as miliary granulomatous infection (e.g. tuberculosis or histoplasmosis). Typically, miliary metastases are less numerous and more variable in size; they may have a mild basilar predominance due to preferential blood flow to the lung bases, and they are sometimes associated with perilymphatic tumour spread. Pleural effusion and enlarged lymph nodes are commonly found.[1-4] Malignant melanoma is a highly aggressive cancer with the potential to metastasize to various locations, such as the lymph nodes, lungs, liver, brain, and bone. Pulmonary metastasis of malignant melanoma commonly presents as solitary or multiple solid nodules, sub-solid nodules, or miliary opacities on CT.[5] In conclusion, CT can help to narrow the differential diagnosis of miliary lung diseases. Nodule distribution, associated radiological findings, and clinical features point frequently to a definite etiological diagnosis.