胃粘膜下腫瘍のCT/MRI診断

Submucosal Tumor of the Stomach:CT and MRI Diagnosis

要旨●胃粘膜下腫瘍の診断におけるCTとMRIの有用性について代表的疾患を提示しながら概説した．GISTは胃体部に多く，管腔外に発育し腫瘍内に出血・壊死・囊胞変性を反映した低吸収域をみることが多い．神経鞘腫は境界明瞭な卵型を呈し管外性発育を示す．造影パターンは均一で平衡相に向けて漸増型の増強効果を示す．グロームス腫瘍は胃前庭部に好発し，門脈や脾臓と同様の強く遷延する造影増強パターンを示す．迷入膵は胃幽門前部の大彎に中心陥凹を伴う粘膜下腫瘤を呈する．造影CTでは他病変と比較して病変部の粘膜が高い増強効果を示し，長径/短径比が1.4以上のことが多い．CTとMRIは拡がり診断に役立つのみならず，局在・進展方向・造影パターン・内部性状などの所見を組み合わせることで病理学的診断に迫ることができる．

　We discussed usefulness of the CT and MRI in evaluating for the gastric submucosal tumors, and illustrated several representative cases. GIST（gastrointestinal stromal tumors）most often locate at gastric body and have a tendency of extraluminal extension. GISTs may show central necrosis, hemorrhage or cystic degeneration. Schwannomas show well circumscribed oval shaped mass. On the enhanced CT or MRI, schwannomas may show homogeneous and persistent enhancing pattern. Glomus tumors tend to locate at gastric antrum. On the enhancing study, glomus tumors may show strong and persistent enhancement which is similar to those of portal vein and spleen. Ectopic pancreas predominantly locates at greater curvature of the gastric antrum and shows submucosal tumor with central depression. The prominent enhancement of overlying gastric mucosa and the long diameter/the short diameter ratio greater than 1.4 are found to be significant for differentiating ectopic pancreas from other tumors. CT and MRI are not only useful for evaluating precise tumor extent, but also can speculate pathological diagnosis of gastric submucosal tumors, based on the combined information of location, extension, enhancing pattern, and internal architecture of the tumors.