Imaging findings in carcinomatous encephalitis secondary to malignant melanoma

Background: The case of disseminated cancer cell spreading throughout the brain is called “miliary metastases” or “carcinomatous encephalitis”, a very rare and critical condition (primarily associated with lung and breast cancer) in which there are multiple plaque with a perivascular distribution, made of punctate lesions spread in all the brain. To our knowledge this represents the fourth case of melanotic miliary brain metastases described in the literature, also associated with melanin content of the lesions that is already evident on unenhanced T1-weighted images. Case presentation: A 75-year-old patient with history of metastatic cutaneous melanoma (BRAF V600E mutate, PD-L1 negative) in treatment with dabrafenib and trametinib after 9 years from the diagnosis developed severe cognitive-motor slowing. Contrast-enhanced brain MRI showed miliary enhancing intra-axial brain lesions involving supra- and sub-tentorial regions and also the perivascular spaces, characterized by a bright appearance on unenhanced T1-weighted images without signal hypointensity in T2*-weighted images, as for melanotic pattern. Thus, the radiological diagnosis of “carcinomatous encephalitis” was made. Neurological examination showed an alert and cooperative subject with increased reaction time in verbal and motor responses. No ocular motility disturbances were found, and there were no motor or sensory deficits in the four limbs. The finger-to-nose test was normal, and no coordination deficit was found bilaterally. Blood tests and body temperature demonstrated no signs of ongoing infection. Electroencephalography showed slow and punctate abnormalities in bilateral fronto-temporal regions, with left prevalence. Corticosteroid therapy was started during hospitalization, improving the clinical picture. The patient was then discharged after 4 days in good clinical conditions with the indication to start second-line treatment with ipilimumab and nivolumab and to perform a whole-brain irradiation. Conclusions: Brain MRI plays a crucial role for the non-invasive diagnosis of carcinomatous encephalitis and for the differential diagnosis with other pathologies. Awareness of the existence of this disorder even in patients with melanoma is necessary to avoid diagnostic delays. Miliary brain metastases should be suspected in all melanoma patients with new neurological findings and contrast-enhanced MRI should be performed to assess the real burden of the disease.