Imaging in Oncology (ANSWER)

Answer:

2. findings suggestive of a cavernous hemangioma

Discussion

    Cavernous hemangiomas occur in 0.4% to 7.3% of patients on autopsy and are the most common benign tumors of the liver. Most hemangiomas occur in women. Most are single lesions and less than 5 cm in diameter, but multiple hemangiomas and larger lesions are common. Cavernous hemangiomas are composed of multiple endothelium-lined blood-filled spaces separated by fibrous septa. Calcifications occur rarely. Generally, cavernous hemangiomas are asymptomatic and are found incidentally at surgery, autopsy, or radiologic workup.¹

    The characteristic CT picture of hemangioma is that of a low attenuation area that develops rim enhancement during bolus infusion and gradual filling in of the lesion on delayed images. There may be some suggestion of a central, low-density focus that appears cystic or necrotic. A rapid intravenous bolus of contrast material is suggested, and serial images are obtained following a delay. The progressive contrast enhancement toward the more central parts of the hemangioma on the delayed CT imaging is related to the gradual accumulation and slow washout of the contrast material. In the largest series describing CT findings in hemangiomas, Freeny and Marks² found this "characteristic" pattern of delayed enhancement from periphery to center in only 54% of cases studied. They calculated a 14% probability that, in a patient with cancer, the characteristic hemangioma pattern would in fact be produced by a metastasis (Fig 2).

    Hemangiomas can show an increase in CT density, becoming hyperintense relative to normal liver parenchyma with contrast administration. Alternatively, they may appear to decrease in size as the enhancement produces isodensity relative to the surrounding normal liver parenchyma. Calcifications are rare.

    Magnetic resonance imaging (MRI) has been advocated by some as having higher than 85% specificity for distinguishing hemangioma from metastases, with a characteristic low-signal intensity on T1-weighted images switching to a high-intensity, homogeneous "light bulb" pattern on spin echo images that are heavily T2-weighted.³ This pattern has been shown to be nonspecific for hemangioma, however, and has now been documented in both metastases and hepatic cysts.⁴

Due to these problems with both CT and MRI, a technetium-labeled red blood cell study is recommended for patients with suspected hemangiomas in the liver. Although large lesions can be detected with conventional planar imaging, smaller lesions require the use of single photon emission computed tomography (SPECT) techniques. Birnbaum and Weinreb⁵ compared the technetium-labeled red blood cell study to MRI in 37 patients with suspected liver hemangiomas from prior CT or ultrasound examination. They demonstrated that the radionuclide study has a specificity approaching 100%. Indeed, the radiologic literature includes only four instances of false-positive red blood cell hemangioma studies. Three were produced by hepatocellular carcinoma and one by a hemangiosarcoma. In contrast, MRI has been found to have a false-positive rate of 20%.⁵

    The radionuclide "hemangioma scan" involves the labeling of red blood cells with technetium 99m pertechnetate. The labeled red blood cells are injected into the patient, and immediate static and SPECT imaging of the liver is performed. Initially, hemangiomas typically show a photon-deficient area in the liver parenchyma. At times, there is enhancement of the hemangioma, usually involving the periphery of the lesion. Delayed static and SPECT imaging of the abdomen is performed following a period of two to three hours. Hemangiomas characteristically show increased enhancement and filling in of the photon-deficient region seen on the immediate images (Fig 3A). There is a gradual accumulation of the radioactively labeled red blood cells that are retained within the hemangioma over time (Fig 3B). This leads to a conversion of the photopenic mass into a mass with increased uptake on the delayed images.

References

1. Moss AA, Gamsu G, Genant HK.  Hepatic pathology.  In:  Computed Tomography of the Body.  Philadelphia, Pa: WB Saunders Co; 1983:634-637.

2. Freeny PC, Marks WM.  Patterns of contrast enhancement of benign and malignant neoplasms during bolus dynamic and delayed CT.  Radiology.  1986;160:613-618.

3. Ferrucci JT.  Liver tumor imaging:  current concepts.  AJR Am J Roentgenol. 1990; 155:473-484.

4. Halvorsen RA Jr, Thompson WM.  Imaging primary and metastatic cancer of the liver.  Semin Oncol.  1991;18:111-122.

5. Birnbaum BA, Weinreb JC.  Definitive diagnosis of hepatic hemangiomas:  MR imaging versus Tc-99m-labeled red blood cell SPECT.  Radiology.  1990;176:95.

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