In 2018, Marek classified lipoma as intraneural lipoma, extraneural lipoma, and lipomatosis of nerve based on the positional relationship between the epineurium and lipoma. Furthermore, he proposed a hybrid type, with combined characteristics of these pathologies. Herein, we describe a hybrid-type lipoma with a radial nerve running inside the tumor. The patient was a 67-year-old female who visited our hospital with a chief complaint of a tumor in her left arm. MRI indicated the radial nerve was running inside the tumor. Although we preserved the nerve during resection of the tumor, postoperative radial nerve palsy, including drop hand and hyperesthesia symptoms, was observed. The wrist drop improved 7 months after surgery, and hyperesthesia improved after 9 months. Hybrid-type lipoma is a rare condition; to our knowledge, only nine cases have been reported. Because it is difficult to separate the nerve from the hybrid-type lipoma during resection, careful dissection under a microscope is desirable.
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