Roentgen Ray 1997
uhrad.com - Abdominal Imaging Case of the Day
Case #2
by: Thomas Herbener, M.D.
Diagnosis: Focal liver enhancement on contrasted CT secondary to SVC obstruction.
Fig. 2A: CT scan through the upper abdomen shows focal enhancement in the medial
segment of the left lobe of the liver adjacent to the falciform ligament (straight
arrow). Note the enhancing venous collaterals on the anterior abdominal wall
(curved arrows).
Fig. 2B: CT scan through the superior mediastinum showing mediastinal lymphadenopathy
(long straight arrow) causing obstruction of the superior vena cava. Note venous
collaterals (curved arrow) on the anterior chest wall communicating with the internal
mammary vein. Note also enhancement within an enlarged azygous vein (short arrow).
Fig. 2C: CT scan at the level of the diaphragm shows anterior thoracoabdominal wall
venous collaterals (short arrows) and a large diaphragmatic collateral (long arrow).
Discussion: With SVC obstruction, various venous collateral pathways exist to shunt blood around the obstruction back to the heart. The main venous collateral pathways include: the azygous-hemiazygous pathway, the internal mammary vein to abdominal wall veins pathway, superficial thoracoabdominal to lateral thoracic veins pathway, and the vertebral venous
plexus.[1] The azygous-hemiazygous pathway predominates unless it is poorly developed or unless obstruction blocks the azygous confluence with the superior vena cava. Then the other pathways will predominate. The case presented here demonstrates focal enhancement in the liver due to superior vena cava obstruction. This focal hepatic enhancement has been reported with superior vena cava obstruction [1-4]. It correlates with the "hot-spot" seen in the liver on a technetium sulfur colloid study in the presence of superior vena cava obstruction [1-6]. Two venous collateral pathways can lead to such enhancement in the liver. One collateral pathway involves anastomosis of the superficial epigastric vein with the patent remnant of the umbilical vein which drains into the left portal vein. Reversed flow of blood within this pathway may cause enhancement in the adjacent liver parenchyma. This venous collateral pathway has been angiographically documented by Lee et al.[2] Paraumbilical veins can communicate through the falciform ligament with the patent remnant of the umbilical vein to the left portal vein and/or directly into the liver. Such veins are usually small; however, they may increase in size with portal hypertension or in the setting of superior vena cava or inferior vena cava obstruction. Other small collateral veins known as rete mirabile may develop in the falciform ligament connecting deep epigastric veins with superficial veins of the abdominal wall and hence lead to direct communication with the abdominal wall and the left portal venous system.[2]
A second pathway may exist described by Ishikawa et al [3]. This pathway explains observed increased contrast enhancement in the liver in the region of the bare area of the right and left lobe due to musculophrenic collaterals with suspected slow flow in the setting of superior vena caval obstruction.
Since in most patients the preferential venous collateral pathway with superior vena caval obstruction is the azygous-hemiazygous pathway, this focal liver enhancement is not commonly seen. In fact, such focal liver enhancement was seen in only one of 22 patients with either superior vena cava, brachiocephalic vein, or subclavian vein obstruction in a series by Bashist et al [1]. This also explains why the so called hot spot is not always seen on radiocolloid uptake liver scans [5,6]. If such focal liver enhancement is identified on a CT scan, investigation for superior vena caval obstruction from such entities as tumor, lymphadenopathy, or even mediastinitis should be further investigated with a chest CT scan.[1-6]
References:
1. Bashist B, Parisi A, Frager DH, Suster B. Abdominal CT findings when
the superior vena cava, brachiocephalic vein, or subclavian vein is obstructed.
AJR 1996;167:1457-1463.
2. Lee KR, Preston DF, Martin NL, Robinson RG. Angiographic documentation of
systemic-portal venous shunting as a cause of a liver scan "hot spot" in superior
vena caval obstruction. AJR 1976;127:637-639.
3. Ishikawa T, Clark RA, Tokuda M, Ashida H. Focal contrast enhancement on hepatic
CT in superior vena caval and brachiocephalic vein obstruction. AJR 1983;140:337-338.
4. Maldjian PD, Obolevich AT, Cho KC. Focal enhancement of the liver on CT:a sign
of SVC obstruction. J Comput Assist Tomogr 1995;19:316-318.
5. Coel M, Halpern S, Alazraki N, et al. Intrahepatic lesion presenting as an area of
increased radiocolloid uptake on a liver scan. J Nucl Med 1972;13:221-222.
6. Holmguest DL, Burdine JA. Caval-portal shunting as a cause of a focal increase in
radiocolloid uptake in normal livers. J Nucl med 1973;14:348-351.
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Submitted by:
Thomas Herbener, M.D.