右側結腸（A:上行結腸、C：盲腸）は図２〜図１４まで，約１２cmにわたり壁が肥厚している．図１０〜図１２で憩室を認め（↑），図７〜図１１で周囲脂肪組織の濃度上昇と後腹膜筋膜肥厚を示し（△），憩室炎である．図１０と図１１の↑が責任病変の憩室である．図１２の１〜図１５の４は虫垂であるが，腫大はなく周囲脂肪組織の濃度上昇も認めず急性虫垂炎の所見ではない．腹部所見で急性虫垂炎と診断され手術となったが，虫垂は軽度の発赤を認める（図A）のみで，盲腸は発赤と炎症性壁肥厚を呈し憩室炎と思われた．病理：catarrhal appendicitis．

参考症例（5mmスライス，盲腸憩室炎）：43歳女性．2日前からの右下腹部痛のため来院した．体温：36.9℃，右下腹部に圧痛と反跳痛がある．
右側結腸（A：上行結腸，C：盲腸）は図８までで，回腸末端（ＴＩ）は図２から始まる．図２〜図７の盲腸（C）は粘膜下浮腫による壁肥厚を呈し，図１〜図６で結腸背側に後腹膜筋膜の肥厚（▲）と脂肪組織の濃度上昇（△）を示し，多発性の憩室（↑）を認めるので憩室炎である．図５と図６の↑が原因の憩室病変であろう．正常虫垂（図８の1〜図１１の8 ）が描出されており，虫垂炎を否定できる．

文献考察：右側結腸憩室炎のUS・CT診断.
Radiology 1998 Sep;208(3):611-8
Right colonic diverticulitis: US and CT findings--new insights about frequency and natural history.
Oudenhoven LF, Koumans RK, Puylaert JB.

PURPOSE: To evaluate how the use of ultrasonography (US) and computed tomography (CT) has changed insights on the frequency and natural history of right colonic diverticulitis. MATERIALS AND METHODS: Clinical findings, US and CT images, and clinical and surgical records in 44 patients with a final diagnosis of right colonic diverticulitis seen over 11 years were retrospectively studied. RESULTS: Of the 44 patients, three underwent diverticulectomy, and 41 were successfully treated conservatively. Follow-up US demonstrated a consistent change in the pattern of the findings of diverticulitis over time, with eventual spontaneous evacuation of the contents of the inflamed diverticulum into the colonic lumen. Five patients had recurrent symptoms; two of them underwent elective surgery. The frequency of right colonic diverticulitis was one in 34 appendectomies, which is nine times higher than that reported to date. CONCLUSION: Right colonic diverticulitis is more common than has been previously reported. US and CT findings are characteristic and show a consistent pattern of changes over time. The natural history is benign, and surgical intervention can be avoided in the vast majority of patients.PMID: 9722836
The CT criterion for the diagnosis of right-sided colonic diverticulitis that we used was direct visualization of the diverticulum as an outpouching of the right-sided ｈｅｍｉｃｏｌｏｎ ａｔ the level of maximum circumferential wall thickening. The diverticulum was expected to contain gas, fluid, or calcified material with hyperattenuating strands in the surrounding fatty tissue adjacent to the diverticulum. There should be no evidence of appendicitis. Disease in the patients was staged according to the method of Netf and vanSonnenherg for the staging of sigmoid diverticulitis. Stage 0 represents the earliest stage of diverticulitis, with only phlegmonous changes around the diverticulum containing a fecalith (Figs 1). Stage 1 implies the presence of a small pericolonic abscess. We introduce here stage R diverticulitis, a residual stage of　the disease after spontaneous evacuation　The diverticulum is empty, and the bowel wall thickening and the amount of surrounding inflamed fat have decreased (Fig 1).

Figure 1. Schematic reconstruction of the natural history of right-sided colonic diverticulitis. The starting point is stage 0 inflammation of the diverticulum, which contains a fecalith and is surrounded by inflamed fat that represents mesentery and omentum. There is local, circumferential thickening of the colonic wall. Evacuation of the contents of the diverticulum takes place either directly (stage 0 evolving to stage R) or by means of the intermediate development of a small pericolonic abscess (stage 0 evolving to stage 1 evolving to stage R). The common end point after spontaneous evacuation is stage R, which is characterized by gradual resolution of the inflammatory abnormalities.