The focal hepatic hot spot sign, also known as the hot quadrate sign can be seen on technetium 99m sulfur colloid scans of the liver and spleen, as well as CT studies.
Radiographic features
It occurs as a focal area of increased radiopharmaceutical uptake, or iodinated contrast accumulation, in the medial segment of the left hepatic lobe (segment IV). This is a pseudolesion caused by abnormal tracer or contrast accumulation due to superior vena cava obstruction (SVCO). In SVCO, if contrast is injected into an upper limb vein, it is diverted into collateral pathways that ultimately direct the flow of blood (and therefore the contrast) into the inferior vena cava in order to reach the right side of the heart. These collateral pathways include the internal thoracic, superior epigastric and inferior epigastric veins, which communicate with paraumbilical veins in the anterior abdominal wall around the umbilicus. The superior and inferior veins of Sappey are the chief paraumbilical veins and carry the blood (and the contrast) to the left lobe of the liver, with direct hepatic parenchymal perfusion as well as drainage into branches of the portal vein. This dual drainage explains the two different densities observed within the area of avid enhancement.
Differential diagnosis
There are other conditions that can result in increased uptake such as:
- hemangioma
- hepatocellular carcinoma
- focal nodular hyperplasia
- hot caudate sign: similar to the hot quadrate sign, but manifests in the caudate lobe, in the setting of a Budd Chiari syndrome
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