Brainstem bloomy rind sign in leptomeningeal metastasis of lung adenocarcinoma

A 70-year-old woman presented to the neurology department with numbness and weakness in extremities for one month.She was diagnosed with lung adenocarcinoma with epidermal growth factor receptor (EGFR) mutation (19del), and had been treated with almonertinib for six months.Neurological physical examination showed stiff-neck, extremities paralysis (2/5 strength), and bilateral Babinski sign.Subsequently, enhanced magnetic resonance imaging (MRI) of the brain revealed a symmetrical hyperintense band along the anterior and lateral surfaces of the brainstem extending to the cerebellar peduncles in T2-FLAIR (Figure 1), and there were no enhancing lesions in the brain parenchyma or leptomeninges.Meanwhile, electroencephalogram (EEG) showed no obvious abnormalities.Combining clinical and imaging presentations, leptomeningeal metastasis or paraneoplastic syndrome was highly suspected and lumbar puncture was carried out immediately.Cerebrospinal fluid demonstrated 1 leucocyte/μl (reference value: < 10 leucocytes/μl), total protein 0.320 g/l (reference value: 0.150-0.450g/l) and paraneoplastic associated antibodies were negative, but cerebrospinal fluid cytology indicated cancer cells carrying EGFR mutation (19del).Taken together, she was definitively diagnosed with leptomeningeal metastasis originating from lung adenocarcinoma.The patient's muscle weakness improved significantly after chemotargeted and neurotrophic treatments.Leptomeningeal metastasis is a complication of malignancy, specifically lung adenocarcinoma, characterized by the dissemination of cancer cells to the pia mater, arachnoid membrane and cerebrospinal fluid. 1 Brain MRI T2-FLAIR hyperintensity on the brainstem surface without abnormal enhancement is a characteristic.It is a peculiar finding that the imaging looks like a bloomy rind on cheese called bloomy rind sign，which is described as a rare marker of leptomeningeal metastasis of lung adenocarcinoma, mainly related to positive EGFR mutations. 2This abnormal imaging may result from an early stage of cancer cells spread in the cerebrospinal fluid space, and cytotoxic edema may be caused by highly cellular infiltrating cancer in the subarachnoid and subpial spaces of the brainstem.This case brings to our attention an exceptional and new MRI pattern or marker of leptomeningeal metastasis that can be used as a guide for clinicians to make a correct diagnosis and give treatment timely.