胞巣状軟部肉腫と診断した小児眼窩腫瘍の1例

An infant of orbital tumor diagnosed as alveolar soft part sarcoma

（P−2-3）　眼窩の胞巣状軟部肉腫は大変稀であり，世界的にも報告例は多くはない。眼瞼腫脹と流涙で発症し，急速に増大した1歳半女児の眼窩腫瘍を経験した。CTでは骨浸潤を伴わない眼球外後方の眼窩内腫瘍で，MRIでは腫瘍内にflow voidを認めた。病理組織学的には胞巣状構造を有し，明瞭な核小体を持つ類円形核を有する腫瘍細胞で，針状結晶は認められなかったが，その前駆物質と考えられているジアスターゼ耐性PAS陽性の顆粒をわずかに認めた。免疫組織化学的にはα-smooth muscle actin，desminなどの筋肉markerやHMB-45, S-100蛋白などが陰性であることより，横紋筋肉腫や明細胞肉腫を除外した。特徴的な針状結晶は確認できなかったが，臨床経過，画像および針状結晶以外の病理所見より胞巣状軟部肉腫と診断した。

A 18-month old female infant developed epiphora and eyelid swelling in her right eye. Computerized tomography showed an orbital tumor without bone infiltration. Magnetic resonance imaging (MRO showed a flow void area within the tumor. Following surgical removal, histopathological studies showed a distinctive alveolar pattern with nest-like prolifera-tion of tumor cells. The cells had vesicular nuclei with distinct nucleoli with little variation in cell size and shape. While no typical needle-shaped crystals were present which is a diagnostic feature of alveolar soft part sarcoma (ASPS) , the tumor had PAS-positive, diastase-resistant granules which appeared to be precursors of these crystals. The diagnosis of rhabdomyosarcoma and clear cell sarcoma could be excluded because of immunohistochemical negativity of a -smooth muscle actin, myoglobulin, desmin, S-100 protein and HMB-45. From these findings, ASPS was the most likely diagnosis for this patient. To our best knowledge, this is the second reported case in Japan.