Congenital absence of the portal vein (CAPV) is a rare malformation of the splanchnic venous system. To our knowledge, only 35 cases of CAPV have been reported in the literature (1–16). The age at diagnosis ranges from 1 day to 64 years. Most cases are accompanied by other anomalies such as cardiac and skeletal malformations and hepatic tumors. Laverdiere et al described the usefulness of magnetic resonance angiography (MRA) to diagnose CAPV noninvasively (1). In this report, we describe a case of a 16-year-old Japanese girl with CAPV who also had hepatic tumors.

A 16-year-old Japanese woman visited Yaizu Municipal Hospital because of nausea and dizziness in September 2001. She had no history of previous disease. Physical examination revealed no abnormal findings except for scoliosis. Laboratory data (Table 1) showed a mild elevation of total bilirubin (2.3 g/dl, normal 0.2–1.0), but serological markers for hepatitis B and C viruses were negative and serum ammonia (NH₃) was normal (47 μg/dl). Abdominal ultrasonography (US) showed a hyperechoic lesion (12 mm in diameter) in segment VI of the liver, and revealed that the portal vein entered directly into the inferior vena cava (IVC) (Fig. 1A, B). The hepatic parenchyma was normal, but no intrahepatic portal vein was detected. Dynamic incremental computed tomography (CT) showed space occupying lesions in segments V and VI of the liver, which appeared as an irregular enhancement with high-density rims. The left portal vein was detectable only within the porta hepatis, and the right and the intrahepatic vein were not detectable. Further, there was dilatation of the common hepatic artery (Fig. 2A–C). Although magnetic resonance imaging (MRI) with T1 and T2-weighted images failed to clearly demonstrate a space occupying lesion, magnetic resonance angiography (MRA) demonstrated a direct connection of the portal vein with the IVC (Fig. 3A, B). CT imaging also confirmed these findings. The early phase of contrast MRA revealed simultaneous enhancement of the IVC, the right atrium and the right ventricle demonstrating the existence of a porto-systemic shunt. Based on these findings, we diagnosed this case as CAPV with hepatic tumors. As the patient refused a needle biopsy, no histological diagnosis for the tumors was obtained. Therefore, a diagnosis of the liver tumors was made tentatively only with the several imaging findings. In this patient, there were no typical CT findings of focal nodular hyperplasia (FNH) for the liver tumors such as the presence of central scar or contrast-enhancement of tumor on early phase images. However, we currently suppose that these tumors seem to be FNH, because CT findings revealed an irregular enhancement with high density rims described previously as an atypical feature of FNH (17). In addition, frequent occurrence of FNH in patients with CAPV has been reported in the literature, and further hepatitis virus infections are absent in this case. Monitoring of the tumors has continued for 18 months, during which time they have shown no evidence of enlargement or expansion. The patient has been clinically well with no episodes of encephalopathy.

CAPV is an extremely rare anomaly that is defined as a congenital loss of the portal vein accompanied by an abnormal drainage of the supramesenteric and splenic veins directly into the systemic circulation. These veins normally anastomose to form the portal vein outside the liver. Development of the portal vein is initiated by selective involution of peri-intestinal vitelline venous loops between the 4th to 10th weeks of gestation (1). Abnormal involution can lead to a preduodenal, prebiliary, or duplicated portal vein, and further excessive involution can result in absence of the portal vein (2). Morgan and Superina classified CAPV into two types, depending on the pattern of the anastmosis between the portal vein and the IVC: type I, in which the entire blood supply from the portal vein drains into the IVC; and type II, in which the blood supply from the portal vein partly drains into the IVC through a side-to-side anastmosis (2). The present case corresponds to type II.

Anatomical loss of the portal vein accompanied by abnormal blood drainage from the portal vein is required for a definite diagnosis of CAPV. Traditionally, conventional angiography has been used to obtain direct vascular images. Recently, we have seen the advent of several new modalities for abdominal imaging, and MRA has proved to be a reliable and non-invasive diagnostic technique for imaging portal system, especially in children (1, 3). MRA clearly demonstrated the absence of the portal vein in the present patient, enabling a diagnosis of CAPV. In addition, US combined with echo-color doppler examination revealed the porto-systemic shunt clearly, which highlights the potential of this technique as a convenient and non-invasive screening examination.

There is the possibility of hepatic dysfunction in patients with CAPV due to insufficient hepatic circulation that is supplied only by a dilatated hepatic artery. However, hepatic encephalopathy rarely ensues in such patients (4), many of whom have normal or only mildly elevated serum levels of liver transaminase and ammonia. The physiological mechanisms that allow patients with CAPV to compensate for chronically impaired hepatic circulation and avoid serious hepatic dysfunction, remain unknown. Kamiya et al proposed that alterations in bacterial intestinal flora induced by an extraordinary entero-hepatic circulation may provide a homeostatic mechanism for maintaining liver function in patients with CAPV (5). Starzl et al speculated that hormonal factors, such as insulin and/or glucagons, in the mesenteric vein might play a role in supporting the integrity of hepatic structure and function (18), thereby keeping liver function quiescent persistently. In the present patient, the initial blood ammonia level (47 μg/dl) was within the normal range, and there was absence of hepatic dysfunction even when the subsequent level fluctuated and reached 107 μg/dl in July 2002 during the follow-up period.

CAPV has been frequently associated with other anomalies outside the abdominal cavity, such as cardiac and skeletal malformations. In the present patient, cardiac US examination failed to detect any cardiac anomalies, however, the patient displayed severe scoliosis, which may be closely associated with CAPV. It is worth noting that a high proportion of patients with CAPV presents with malignant or benign liver tumors (Table 2). A total of 35 patients with CAPV has been reported in the literature, of which 16 CAPV patients had several kinds of hepatic tumor. Seven patients had focal nodular hyperplasia (FNH) or FNH-like lesions, 2 patients had nodular regenerative hyperplasia (NRH), 2 patients had hepatocellular carcinoma, 2 patients had hepatoblastoma, 2 patients had adenoma and 1 patient had benign hepatic tumor. Kondo et al demonstrated histologically abnormal vascularization of the portal system with abnormal arterial vascularization, in the livers of patients with FNH, NRH, and FNH-like large regenerative nodules (LRN) (19). Consequently, they hypothesized that abnormal circulation of the portal system in an affected liver may provide an environment for the development of neoplastic tumor. Similarly, it is likely that disequilibrium of hepatic circulation between the hepatic artery and portal vein may mainly cause tumor development in patients with CAPV (16).

Morse et al reported a patient with CAPV who underwent liver transplantation for hepatoblastoma that was initially diagnosed FNH 2 years previously (6, 7). This suggests that long-term follow-up and monitoring for malignancy should be mandatory, even with an initial diagnosis of benign tumor. Although there were no imaging results of the lesions as definite malignancy in our patient, histological examination of the tumors was not performed. Further uncertainty with the diagnosis also remains because of the reduced accuracy of interpreting images obtained in cases of chronically impaired and abnormal hepatic circulation.

In summary, we have described a patient with CAPV with concurrent liver tumors. This patient displayed no hepatic dysfunction and had no obvious findings consistent with liver malignancy. Since histological evaluation of the tumors has not been performed, we are continuing careful monitoring for the development of neoplastic liver tumors using several imaging modalities on a three- to six-month basis.