乳児血管腫と鑑別を要したNTRK-rearranged spindle cell neoplasmの1例

A Case of NTRK-Rearranged Spindle Cell Neoplasm Mimicking Infantile Hemangioma

はじめに

　NTRK-rearranged spindle cell neoplasm（以下，NTRK-RSCN）は骨軟部腫瘍WHO分類第5版から新しく収載・定義されたまれな軟部腫瘍群である 2）。20歳までの若年者に発生し，四肢や体幹の表層から深層に認められることが多いとされ，形態や病理組織学的グレードに幅があり低悪性度から高悪性度のものまでさまざまである 2）。一方，乳児血管腫は乳幼児期に最も多い腫瘍で，多くは肉眼的に診断が可能である 3）が，まれにほかの血管性病変や腫瘍との鑑別を要することがある。今回われわれは初診時に乳児血管腫と診断されたが非典型的な経過をたどり，最終的にNTRK-RSCNの診断に至った症例を経験したので臨床経過について報告する。

　Neurotrophic tyrosine receptor kinase (NTRK)-rearranged spindle cell neoplasm (NTRK-RSCN), newly described in the 5th edition of the WHO classification for Soft Tissue and Bone Sarcomas, is a rare soft tissue tumor that is usually observed in individuals <20 years old and often develops at superficial and/or deep regions of the extremities as well as the trunk. This neoplasm also shows a wide range of histologic grades.

　An infantile hemangioma is the most common benign tumor of childhood, and it can be diagnosed with a careful examination and macroscopic findings. It must occasionally be distinguished from other vascular lesions or malignant tumors. We present the case of a 4-year-old boy with a tumor at the middle forehead. The initial diagnosis was an infantile hemangioma. The tumor showed mild shrinkage when the patient was 35 months old but had re-expanded and become firm approx. 1 month later at the age of 4 years. Based on the atypical clinical course and the suspicion of an infantile hemangioma, ultrasound and MRI/MRA studies were carried out but the definitive diagnosis was not obtained. The pathological study demonstrated that the tumor was a low-grade NTRK-RSCN. No recurrence of the lesion was observed over the 28-month follow-up period after surgical extirpation.