'Hot cross bun' sign with leptomeningeal metastases of breast cancer: a case report and review of the literature

Background: The 'hot cross bun' (HCB) sign refers to a cruciform-shaped hyperintensity within the pons found on T2-weighted magnetic resonance imaging (MRI). It is commonly associated with atrophy of the pons, cerebellum, and putamen in multiple system atrophy (MSA). In this report, we describe a rare case of the HCB sign in an adult female patient with leptomeningeal metastases of breast cancer without any signs of brain atrophy. Case presentation: The patient was a 58-year-old woman diagnosed with grade 2 ductal breast carcinoma, who had undergone a right mastectomy, followed by chemotherapy treatments and chest wall radiotherapy. The tumor had metastasized to the skin, and the patient presented with vomiting, drowsiness, and intermittent episodes of confusion, slurred speech, and involuntary movements. Immunohistochemical staining demonstrated a triple-negative status of the tumor. Axial T1-weighted MRI showed a linear enhancement in the cerebellar sulcus. A diagnosis of leptomeningeal metastases of breast cancer was confirmed by detection of tumor cells in the cerebrospinal fluid. Axial T2-weighted MRI indicated a cruciform hyperintensity in the pons without any atrophy of the pons, cerebellum, or putamen. Conclusion: The HCB sign can occur with leptomeningeal metastases of solid tumors, though the underlying mechanisms remain unknown.