LAUSR

Rationale: Nodular fasciitis (NF) can be misdiagnosed as a sarcoma because of its rapid growth and pathological features, such as nuclear atypia and mitoses. Patient concerns: We present a rare case of a 72-year-old Japanese man who developed NF with suspected postirradiation myxofibrosarcoma (MFS) after segmentectomy for left-sided osteoradionecrosis (ORN) of the mandible. Diagnosis: A mass appeared in the intraoral postoperative wound 1 year after left-sided mandibular segmentectomy and showed rapid growth, reaching a size of 50 mm within 2 months. Incisional biopsy revealed strongly Ki-67-positive spindle-shaped cells with large irregular nuclei and a diagnosis of postirradiation MFS. Interventions: The patient was diagnosed with oropharyngeal cancer (T4aN2bM0) and underwent surgical resection of primary oropharyngeal squamous cell carcinoma with selective neck dissection and reconstruction with a rectus abdominis musculocutaneous flap at the age of 57 years, followed by postoperative 66 Gy of radiotherapy combined with cisplatin administration. No recurrent or metastatic lesions of oropharyngeal squamous cell carcinoma have been detected for > 10 years. However, the ORN of the jaw worsened, and the patient underwent sequestrectomy 3 times on the right side of the mandible, followed by a left-sided segmentectomy at the age of 72 years. One year after segmentectomy, a 10-mm mass with soft-to-firm consistency appeared in the buccal mucosa of the wound and grew rapidly. An incisional biopsy revealed MFS. Complete resection under general anesthesia was immediately performed. Outcomes: The histopathological diagnosis of the excised specimen was NF without any malignant findings. Two years after surgery, there was no evidence of recurrence or metastasis. Lessons: NF grows rapidly and has pathological features similar to sarcoma, making differential diagnosis difficult at the time of incisional biopsy. Further studies should be conducted to determine the clinical and pathological features of this tumor.