A 50-year-old woman presented with a mass in the upper outer quadrant of her left breast, which proved to be a mucinous cystadenocarcinoma by biopsy. An 18F-FDG PET/CT was performed for staging, which showed that the breast tumor was the only lesion with abnormal 18F-FDG avidity. Breast-conserving surgery was performed following a negative sentinel lymph node biopsy of the left axilla, and primary mucinous cystadenocarcinoma of the breast was finally diagnosed.

Rationale: Disseminated cryptococcosis is extremely rare and is easily misdiagnosed as a malignant lymphoma. 18 F-Fluorodeoxyglucose Positron Emission Tomography (PET)/ computed tomography (CT) may be useful to assess the involvement of disseminated cryptococcosis and to evaluate residual disease after treatment.Patient Concerns: A 21-years-old man presented with fever and cough for a month, with multiple red nodules scattered on the skin. 18 F-Fluorodeoxyglucose PET/CT revealed multiple hypermetabolic lymph nodes in the upper and lower parts of the diaphragmatic region and hypermetabolic nodules in the skin. According to the PET/CT results, malignant lymphoma was considered a possibility, especially T-cell lymphoma involving the skin.Diagnosis: Cryptococcosis was diagnosed using inguinal lymph node biopsy and blood culture. Interventions:The patient received two months of amphotericin B, fluconazole, and half a month of meropenem.Outcomes: The patient's body temperature returned to normal and the red nodules on the skin disappeared. Most of the hypermetabolic enlarged lymph nodes disappeared, which was confirmed by reexamination with PET/CT.Lessons: Disseminated cryptococcosis is easily misdiagnosed as malignant lymphoma, especially when the lymph nodes are more involved. When multiple hypermetabolic enlarged lymph nodes appear on PET/CT, except for lymphoma, specific infections should also be considered.