単純CT（図１〜図８）と造影後期相（Late：図１７〜図２３）で肝左葉と右葉にdensityの差がないのに，造影早期相（Early：図９〜図１６）では右葉に比べ左葉が濃染しているのは何故か？　図１６から門脈（PV：Portal Vein）を頭側へ追跡すると，門脈右枝は開存しているが，左枝（↑）は造影効果を認めず閉塞しており血栓症を強く示唆する．左葉は門脈血流がないために代償性に動脈が拡張し動脈血流が増加している現象である．図Aの上腸間膜動脈造影の門脈相で左枝が造影されないことでCT所見が証明された．

参考症例（肝内門脈右枝血栓症）：42歳男性．既往歴：6年前胆嚢摘出術．1週間前に上腹部痛と発熱が出現し，3日前から外来での抗生物質投与に反応せず症状が続いている．体温：38.4℃，心窩部に圧痛があるのみ．図１〜図８は造影早期相（Early），図９〜図１２は造影後期相（Late）．上記症例同様に造影早期相で肝左葉と右葉にdensityの差があるのは，門脈右枝（↑）が血栓症により閉塞しているからだと思われる．図２〜図７の低濃度域▲は肝静脈の閉塞を意味する所見であろう（下記文献）．△は造影早期相で壁の一部が濃染され，後期相でリング状濃染となり厚くなっているので膿瘍であることを強く示唆するが，患者の希望で転院したのでその後の経過は不明である．

文献考察：肝膿瘍例で門脈が閉塞すると代償性に動脈血流が増加して高濃度領域を呈する現象が67％に見られ，肝静脈が閉塞すると動脈門脈瘻が形成されるため逆に低濃度領域を示す現象が35％に見られた．
AJR Am J Roentgenol. 2005 Oct;185(4):1015-23.
Hepatic attenuation differences associated with obstruction of the portal or hepatic veins in patients with hepatic abscess.
Lee KH, Han JK, Jeong JY, Kim YJ, Lee HJ, Park SH, Choi BI.

OBJECTIVE: The purpose of our study was to determine the nature of the association between the attenuation difference of the hepatic parenchyma surrounding an abscess and obstruction of the regional portal vein or of the hepatic vein. MATERIALS AND METHODS: Helical CT scans of 60 patients with hepatic abscess were analyzed for the presence of complete or partial obstruction of the portal or hepatic veins and for attenuation differences in the surrounding parenchyma. Clinical (age, sex, underlying disease, and microorganism) and CT (obstruction of the portal or hepatic vein and number, location, and size of abscesses) findings were analyzed statistically for possible associations with each of regional parenchymal hyper- and hypoattenuation by using the chi-square test and multivariate logistic regression analysis. RESULTS: Regional parenchymal hyperattenuation was identified in 40 patients (67%). More patients with portal vein obstruction showed regional parenchymal hyperattenuation than patients without portal vein obstruction (22/27 patients vs 18/33, p = 0.028), and more patients with hepatic vein obstruction showed regional parenchymal hypoattenuation than those without hepatic vein obstruction (11/21 vs 3/39, p = 0.0003). Multivariate logistic regression analysis showed that portal venous obstruction was the only statistically significant predictor of regional parenchymal hyperattenuation (p = 0.032; odds ratio, 3.7) and that parenchymal hypoattenuation was associated with hepatic venous obstruction (p = 0.001; odds ratio, 44.9). CONCLUSION: Parenchymal hypo- and hyperattenuation are frequently observed in the hepatic region surrounding an abscess on dynamic CT. Moreover, these parenchymal attenuation differences are associated with regional portal or hepatic vein obstruction.PMID: 16177426