DOI: 10.1148/radiol.2372031690
(Radiology 2005;237:647-648.)
© RSNA, 2005
The Focal Hepatic Hot Spot Sign1
Asante M. Dickson, MD
1 From the Department of Radiology, Winthrop-University Hospital, 259 First St, Mineola, NY 11501. Received October 30, 2003; revision requested January 8, 2004; revision received February 2; accepted February 16.
Address correspondence to the author (e-mail: amd10{at}cornell.edu).
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APPEARANCE
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The focal hepatic hot spot sign can be observed on technetium 99m (99mTc) sulfur colloid scans of the liver and spleen. This sign is seen as a focal area of increased radiopharmaceutical uptake in segment IV of the liver (Fig 1) (1).
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Figure 1. Anterior 99mTc–sulfur colloid scans in patient with superior vena cava obstruction secondary to large mediastinal mass show focal areas of increased radiotracer uptake (arrows) in medial segment of left hepatic lobe. 99mTc–sulfur colloid scans are same image, one (right) being of greater intensity.
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EXPLANATION
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In the presence of superior vena cava obstruction, the left hepatic lobe may occasionally demonstrate areas of focally increased blood flow in the collateral veins that can be seen on images. Typically, the collateral venous pathway comprises the internal mammary vein that connects to the left portal vein via the paraumbilical vein (1,2). The flow of blood through the collateral veins may result in areas of focally increased blood flow to the liver (1,2). Specifically, an area of increased activity in segment IV of liver (ie, within the medial segment of the left hepatic lobe in what was formerly known as the quadrate lobe) has been well documented in patients with superior vena cava obstruction; this area of increased activity can be seen on 99mTc–sulfur colloid scans of the liver and spleen and is referred to as the focal hepatic hot spot sign (1). The equivalent of this sign may also be seen on contrast material–enhanced computed tomographic (CT) scans (Fig 2). Some other causes of hepatic hot spots include Budd-Chiari syndrome, liver abscess, hemangioma, focal nodular hyperplasia, and hepatocellular carcinoma (2,3). With the exception of Budd-Chiari syndrome, which causes the hot spot sign to occur in the caudate lobe, all other entities can cause the hot spot sign to occur anywhere in the liver, including segment IV.
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Figure 2. Transverse CT scan of abdomen in different patient than shown in Figure 1 demonstrates hypervascular region (arrows) in segment IV of liver that represents CT equivalent of focal hepatic hot spot sign. Note enlarged subcutaneous collateral vessels (arrowheads) with superior vena cava obstruction owing to mediastinal extension of lung carcinoma. Left pleural effusion is present.
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DISCUSSION
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A focal area of increased activity, or hot spot, in segment IV of the liver may be seen on 99mTc–sulfur colloid scans of the liver and spleen in patients with superior vena cava obstruction. The hot spot sign is believed to be caused by portosystemic venous shunting between the superior vena cava and the portal vein. Within the liver, the hot spot is created by areas of focally increased blood flow that result from this shunting. The distribution of 99mTc–sulfur colloid activity in the liver varies depending on the preferential flow of blood within the left portal vein and on the intrinsic anatomic characteristics of the patient's vascular system (4).
There are numerous routes by which collateral vessels attempt to bypass central venous obstruction. In the thorax, three major collateral venous pathways are available: the superior route, the posterior route, and the anterolateral route (5). The superior route is seen in cases of distal central venous obstruction (subclavian or brachiocephalic) and involves the anterior jugular venous system (5,6), which connects the subclavian and internal jugular veins. The posterior route comprises both the azygous-hemiazygous and paravertebral systems (5). Identification of either of these collateral pathways at cross-sectional imaging should strongly suggest superior vena cava obstruction. The anterolateral system connects the anterior intercostal, internal mammary, and long thoracic veins to the inferior vena cava via the pericardiophrenic, musculophrenic, lumbar, and hepatic veins (5).
As in patients with superior vena cava obstruction, patients with inferior vena cava obstruction may demonstrate the hot spot sign in segment IV of the liver if 99mTc–sulfur colloid is injected into a lower extremity vein. In this situation, venous blood will preferentially shunt to segment IV of the liver via collateral pathways (7).
In summary, in a patient with obstruction of the superior vena cava, collateral veins return blood to the left hepatic lobe via the internal mammary and left umbilical veins, thereby creating a hot spot in the area of insertion of the left umbilical vein and left main branches of the portal vein. The hot spot can be seen as a focal area of hyperattenuation at arterial or early portal venous CT (6) or as a focal accumulation of radionuclide in segment IV secondary to collateral venous flow through the liver at nuclear imaging. When observed, the focal hepatic hot spot sign should strongly suggest central venous obstruction in the thorax.
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ACKNOWLEDGMENTS
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I thank Douglas S. Katz, MD, Elizabeth Yung, MD, and Christopher J. Palestro, MD, for their assistance in the preparation of this article.
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FOOTNOTES
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A trainee (resident or fellow) wishing to submit a manuscript for Signs in Imaging should first write to the Editor for approval of the sign to be prepared, to avoid duplicate preparation of the same sign.
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References
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- Yamada T, Takahashi K, Shuke N, et al. Focal hepatic "hot spot" in superior vena cava obstruction: correlation between radiocolloid hepatic SPECT and contrast-enhanced CT. Clin Nucl Med 1999;24:533–534.[CrossRef][Medline]
- Muramatsu T, Miyamae T, Mashimo M, Suzuki K, Kinoshita S, Dohi Y. Hot spots on liver scans associated with superior or inferior vena caval obstruction. Clin Nucl Med 1994;19:622–629.[Medline]
- Welch TJ, Sheedy PF, Johnson CM, et al. Focal nodular hyperplasia and hepatic adenoma: comparison of angiography CT, US, and scintigraphy. Radiology 1985;156:593–595.[Abstract/Free Full Text]
- Yun M, Kim CK, Krynyckyi BR, Machac J. Incidental recognition of left subclavian vein obstruction on renal scintigraphy. Clin Nucl Med 2001;26:610–612.[CrossRef][Medline]
- Gosselin MV, Rubin GD. Altered intravascular contrast material flow dynamics: clues for refining CT diagnosis. AJR Am J Roentgenol 1997;169:1597–1603.[Abstract/Free Full Text]
- 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.[Medline]
- Habibian MR, Delbeke D, Martin WH, Sandler MP. Nuclear medicine imaging: a teaching file. Philadelphia, Pa: Lippincott Williams & Wilkins, 1999;320–321.
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