消化管脂肪腫の診断と治療

Diagnosis and Treatment of Lipoma in the Alimentary Tract

要旨　消化管における脂肪腫は大腸に最も多く発生し，次いで十二指腸・小腸，胃，食道の順である．消化管非上皮性良性腫瘍の中に占める脂肪腫の割合は，大腸では最も高く，十二指腸・小腸では平滑筋腫に次いで高く，食道や胃では非常に低い．脂肪腫は，無茎性から有茎性の表面平滑な黄色調の柔らかい粘膜下腫瘍で，特徴所見としてsqeeze sign，cushion sign，naked fat signがある．粘膜下層に主座を置く内部が均一な腫瘍で，超音波検査では高エコー，CT検査ではlow density，MRI検査ではT1強調像でhigh intensity，T2強調像でiso intensityな腫瘤として描出される．しばしば，腸重積の原因となり，蟹爪様所見，coiled-spring appearance，target signあるいはmultiple concentric ring signを呈する．また，腸重積を繰り返すと，循環障害のため腫瘍表面に炎症，びらん，潰瘍を生じ，そのため腫瘍表面は凹凸不整で発赤調を呈し，上皮性腫瘍との鑑別は困難となる．病理組織学的には成熟脂肪細胞の増生と少量の血管を含む結合織から成る良性腫瘍である．脂肪腫は，出血や閉塞症状を来すものは治療の対象となり，内視鏡摘除や外科的切除術が施行される．

　The occurrence of lipomas in the alimentary tract is most common in the colon, but although they can be found also in the duodenum and the small bowel, their occurrence is very rare in the stomach and the esophagus.

　Lipomas are yellowish and soft submucosal tumors. They show various forms sessile to pedunculated types. Their characteristic findings in X-rays and in endoscopy are “squeeze sign”,“cushion sign” and “naked fat sign”. Moreover they demonstrate high echolevel tumor in ultrasonography and low density tumor in CT scans. Their MRI findings are high intensity in T1weighed axial scanning and iso intensity in T2scanning.

　Most lipomas cause no symptoms but the larger ones may develop symptoms including bleeding, intussusception and obstruction, etc. When they cause intussusception, “concave pressure defect”, “coiled-spring appearance” and “target sign or multiple concentric ring sign” are demonstrated in X-rays, ultrasonography and CT. In the case of repeated invagination, their surface shows redness and granularity mimicking epithelial neoplasms due to inflammation, erosion and ulceration.

　Microscopically, a lipoma is a benign tumor made up of a fibrous capsule containing mature adipose tissue lobules and thin fibrovascular septa. In the case in which a lipoma should develop serious symptoms, such as massive bleeding and obstruction, it should be endoscopically or surgically removed.

　1) Internal Medicine II, Osaka Medical College, Takatsuki, Japan

　2) Gastrointestinal Division, Ishikiri Seiki Hospital, Higashi-Osaka, Japan

　3) Pathology I, Osaka Medical College, Takatsuki, Japan