Antenatal diagnosis of an extrahepatic portal vein aneurysm.

To the Editor: We are writing to report an infant antenatally diagnosed with an extrahepatic portal vein aneurysm. A healthy 30-year-old female underwent an antenatal sonogram at 34 weeks' gestation. A large flowing vessel was noted near the midline, in proximity to the caudate lobe of the liver. Following an otherwise unremarkable pregnancy, a boy weighing 3,145 g was born via repeat cesarean section at 39 weeks' gestation. At birth, the physical examination was normal. Physiologic jaundice resolved without treatment. An abdominal sonogram performed on the first day of life showed a portal vein aneurysm at the junction of the splenic and superior mesenteric veins measuring 1.5 X 0.8 cm, with venous flow confirmed by color flow and duplex Doppler sonography. The infant underwent a follow-up study at one month and at one year, showing no change in the size of the aneurysm. The child remains asymptomatic.

Portal vein aneurysms are rare anomalies of unknown etiology. Since being first described in 1956, fewer than 60 cases have been reported. (1-3) The cause of portal vein aneurysms remains controversial, with proposed etiologies including a developmental anomaly, congenital weakness of the venous wall, or acquired weakening of the vessel due to portal hypertension or inflammation. (4) In the absence of an apparent acquired postnatal cause such as weakening of the portal vein vessel due to inflammation or portal hypertension, cases of aneurysmal dilation of the portal vein have been attributed to a venous anomaly related to abnormal development.

Normal splanchnic venous development provides insight into the potential developmental anomaly that may lead to these aneurysms. The portal vein develops from the paired vitelline veins and their communications. Three anastomoses form between the right and left vitelline veins by the fourth week of gestation. The most cranial is located at the porta hepatis, the middle in a retroduodenal position, and the most caudad distal to the origin of the common bile duct. The portal vein forms from the most cranial portion of the right vitelline vein, the middle anastomosis, and the caudad portion of the left vitelline vein following regression of the remaining portions of the venous plexus. The most common sites for portal vein aneurysms are at the confluence of the splenic and superior mesenteric veins (as was found in the patient in the current report), in the main portal vein, and in the intrahepatic portal vein at branching sites. (5) Incomplete regression of portions of the vitelline veins and their anastomoses may account for portal vein aneurysms observed at these locations.

The current case supports a possible developmental defect as the cause of portal venous aneurysms first identified in older children and adults.

References

1. Barzilai RE, Kleckner MS. Hemocholecyst following ruptured aneurysm of portal vein. Arch Surg 1956;72:725-727.

2. Ohnami Y, Ishida H, Konno K, et al. Portal vein aneurysm: report of six cases and review of the literature. Abdom Imaging 1997;22:281-286.

3. Arda K, Kizilkanat KT, Tosun O, et al. Portal vein aneurysm; CT, MR, and MR angiography appearances. Acta Gastroenterol Belg 2002;65:136-138.

4. Fulcher A, Turner M. Aneurysms of the portal vein and superior mesenteric vein. Abdom Imaging 1997;22:287-292.

5. Gallego C, Velasco M, Marcuello P, et al. Congenital and acquired anomalies of the portal venous system. Radiographics 2002;22:141-159.

Raquel Gomez, MD

Danielle M. Bentsen, MD

Randall S. Burd, MD, PHD

Department of Surgery, Division of Pediatric Surgery, Robert Wood Johnson Medical School, and Department of Radiology, Robert Wood Johnson University Hospital, New Brunswick, NJ