Cavernous hemangioma is the most common primary liver tumor; its occurrence in the general population ranges from 0.4-20%, as reported by Karhunen in an autopsy series.  Cavernous hemangiomas arise from the endothelial cells that line the blood vessels and consist of multiple, large vascular channels lined by a single layer of endothelial cells and supported by collagenous walls. These tumors are frequently asymptomatic and incidentally discovered at imaging, surgery, or autopsy. Hemangiomas are uncommon in cirrhotic livers; the fibrotic process in cirrhotic liver may prohibit their development.  The radiologic characteristics of hemangiomas are demonstrated in the images below.
Usually, cavernous hemangiomas occur as solitary lesions; however, they may be multiple in as many as 50% of patients.  No lobar predilection exists, and the tumors may be associated with focal nodular hyperplasia.  Hemangiomas typically measure less than 5 cm; those larger than 4-5 cm are sometimes called giant hemangiomas. [5, 6, 7]
Most hemangiomas are incidentally detected on imaging studies. Ultrasonography is a cost-effective imaging modality for the diagnosis of a hemangioma. However, computed tomography (CT) scanning and/or magnetic resonance imaging (MRI) may be required to specifically diagnose a hemangioma. Ultrasonography is a heavily operator-dependent technique; its performance depends on the expertise and experience of the ultrasonographer. In addition, the acquisition of satisfactory images in obese patients is technically difficult. Contrast-enhanced CT scanning is relatively contraindicated in patients who have renal insufficiency and in those who have a previous history of hypersensitivity to iodinated contrast agents; thus, MRI may be the preferred modality of choice in the characterization of hemangiomas in such patients. Angiography is an invasive method that is used for the characterization of liver hemangiomas; this imaging modality is associated with low, but definite, risks of morbidity and mortality. [8, 9, 10, 11, 12, 13, 14]
Kobayashi et al found a sensitivity of 79% and a specificity of 100% for the diagnosis of hepatic hemangioma using contrast-enhanced ultrasonography (CEUS) with Levovist. Liver-specific findings were affected by taking early-phase ultrasonograms or changing the posture of the patient. 
Hemangiomas are enhancing lesions that have characteristic dynamic features after the administration of contrast material. On nonenhanced CT scans, hemangiomas appear hypoattenuating relative to the adjacent liver. Calcification is uncommon; it may be marginal or central, spotty or chunky.  During the arterial-dominant phase, small hemangiomas show intense and uniform contrast enhancement and retain their contrast enhancement during the portal venous phase. (See the image below.) [4, 16, 9]
Wedge-shaped subcapsular or segmental perilesional enhancement may be noted adjacent to high-flow hemangiomas. These findings are possibly due to hemodynamic alterations in the liver.  The pattern of a peripheral, discontinuous, intense nodular enhancement during the arterial-dominant phase with progressive centripetal fill-in on CT scans is considered pathognomonic for hemangiomas (see the image below). Pathologically, the nodular areas consist of small vascular spaces that are more densely packed than the rest of the lesion.
Degree of confidence
Hemangiomas that show early, homogeneous contrast enhancement on dynamic CT scans and/or MRI may be mistaken for other hypervascular liver tumors such as hepatoma, focal nodular hyperplasia, adenoma, and hypervascular metastases. The absence of a history of cirrhosis and/or primary malignancy is an important factor in diagnosing hemangioma. The characteristic features of a hemangioma on dynamic CT scanning, red blood cell scintigraphy, and/or MRI permit confident diagnosis in more than 95% of cases.
Magnetic Resonance Imaging
MRI is more sensitive and specific than other imaging modalities in the diagnosis of hemangiomas. Hemangiomas appear as smooth, lobulated, homogeneous, sometimes septated, hypointense lesions on T1-weighted images. On T2-weighted images, they appear hyperintense relative to the liver (ie, more pronounced on fast spin-echo images), and they remain as bright as cerebrospinal fluid or bile with increased echo time (TE). (See the image below.) [22, 10]
The high signal intensity on T2-weighted images is due to the extremely long T2 relaxation time of the free fluid (ie, slowly moving blood). The T2 relaxation time is directly proportional to the collective size of the hemangioma's constituent vascular spaces.  The T2 values for hemangiomas vary between 90 and 200 msec, compared with T2 values >300 msec for cysts.
Rarely, the imaging features of heavily fibrotic (hyalinized) hemangiomas can be mistaken for those of metastases.  With the injection of contrast material (gadolinium chelates), lesions typically demonstrate peripheral nodular enhancement with progressive, centripetal fill-in that usually appears after 5-30 minutes. (See the image below.)
Large hemangiomas may appear cystic on images as a result of recurrent hemorrhage or myxomatous degeneration. In some hemangiomas, MRI may demonstrate fluid-fluid levels due to the sedimentation of blood products. The supernatant layer consists of unclotted serous blood, and the sediment consists of red blood cells. Definitive diagnosis is often difficult. 
Gadolinium-based contrast agents (gadopentetate dimeglumine [Magnevist], gadobenate dimeglumine [MultiHance], gadodiamide [Omniscan], gadoversetamide [OptiMARK], gadoteridol [ProHance]) have been linked to the development of nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD). For more information, see the eMedicine topic Nephrogenic Systemic Fibrosis. The disease has occurred in patients with moderate to end-stage renal disease after being given a gadolinium-based contrast agent to enhance MRI or MRA scans.
NSF/NFD is a debilitating and sometimes fatal disease. Characteristics include red or dark patches on the skin; burning, itching, swelling, hardening, and tightening of the skin; yellow spots on the whites of the eyes; joint stiffness with trouble moving or straightening the arms, hands, legs, or feet; pain deep in the hip bones or ribs; and muscle weakness. For more information, see Medscape.
Degree of confidence
MRI is more sensitive and specific than other imaging modalities in the diagnosis of hemangiomas. On the basis of liver hemangioma characteristics on T2-weighted images (morphologic and quantitative T2 values), MRI has a sensitivity of 100%, a specificity of 92%, and an accuracy rate of 97%.
Hemangiomas that show early, homogeneous contrast enhancement on dynamic CT scans and/or MRI may be mistaken for other hypervascular liver tumors such as hepatoma, focal nodular hyperplasia, adenoma, and hypervascular metastases. The absence of a history of cirrhosis and/or primary malignancy is an important factor in diagnosing hemangioma. The characteristic features of a hemangioma on dynamic CT scans, red blood cell scintigraphy, and/or MRI permit confident diagnosis in more than 95% of cases.
At ultrasonography, hemangiomas appear as well-circumscribed, uniformly hyperechoic lesions (see the image below). The increased echogenicity has been postulated to be caused by multiple interfaces between the walls of the cavernous spaces and the blood within them. 
In a study by Taboury et al, more than 75% of hemangiomas had posterior acoustic enhancement that the authors believed was correlated with hypervascularity at angiography.  In large hemangiomas, heterogeneous areas are interspersed within the hyperechoic mass. Atypical features include hypoechoic lesions with a thin hyperechoic rim or a thick rind and scalloped borders.  Note that hemangiomas may appear hypoechoic in fatty livers. 
Color power or duplex Doppler ultrasound examinations have a limited role in the specific diagnosis of hemangioma.  Occasionally, a kilohertz shift in the low to midrange may be observed in the peripheral and central blood vessels in the hemangiomas. 
Red blood cell–tagged technetium-99m (99m Tc) scintigraphy with single photon emission CT (SPECT) scanning permits a specific diagnosis of hemangiomas.  Hemangiomas characteristically show decreased activity on early dynamic images and delayed filling from the periphery of the lesion.
The reported sensitivity is 97%; the specificity, 83%; and the accuracy, 96%, for red blood cell–tagged99m Tc scintigraphy in the diagnosis of hemangiomas.
At angiography, the feeding vessels of the hemangioma are of normal caliber, except those in the large tumors. During the late arterial/hepatic parenchymal phases, a dense, nodular pattern of opacification of the dilated vascular spaces persists into the venous phase. 
Although hemangiomas have characteristic angiographic features, the use of angiography is not warranted in the diagnosis of hemangioma, given the diagnostic capabilities of less invasive techniques, such as helical CT scanning and MRI.