腹部領域

Misreading and false positive in diagnosis of FDG-PET/CT in the abdominal region

腹部のFDG-PET/CT診断において，見逃しと読み過ぎ，すなわち偽陰性，偽陽性，診断の限界は多岐にわたって存在する。胃癌，肝癌，腎癌，前立腺癌などではFDG集積が低くPETではみえないことがあるのはすでに広く知られているが，種々の炎症によって臓器やリンパ節などに集積を生じることも多数経験する。全身所見からの判断や，過去画像との比較，PET直前の画像との短期の微妙な変化などを手がかりにして推測するが，適切な診断を下すことが難しいことも多い。本稿では，診断に苦慮した自験例を挙げて日々経験する診断の限界や注意点を述べたい。

A lot of pitfalls are hiding in diagnosis of FDG-PET/CT in the abdominal region. The fact that some kind of tumor, like gastric cancer, hepatocellular carcinoma, renal cell carcinoma, and prostatic carcinoma shows weak uptake of FDG is well known. On the other hand, inflammatory change of organs and lymph nodes show hyper accumulation of FDG. This article presents our own cases which were difficult to diagnose. Liver abscess may occur after biliary drainage. It may show high uptake of FDG and mimic liver metastases. Small disseminated lesions are easily missed, and renal metastases are difficult to identify in the strong urinal FDG uptake. Fat necrosis that may occur after chemotherapy of malignant lymphoma shows strong FDG uptake. Consideration of the CT images, its irregular shape and low density, is important for accurate diagnosis. To prevent overlooking and overestimation, it is necessary not only to observe the images（PET, PET/CT, and CT）carefully, but also to compare them with the previous images and to take clinical information into account.