Imaging of Benign Focal Liver Lesions

CONTENTS

4.1 Primary Benign Liver Lesions

4.1.1 Hemangioma

4.1.2 Focal Nodular Hyperplasia

4.1.3 Hepatocellular Adenoma

4.1.4 Nodular Regenerative Hyperplasia

4.1.5 Cysts

4.1.6 Miscellaneous Tumors

4.1.6.1 Lipomatous Tumors

4.1.6.2 Leiomyoma

4.2 Secondary Benign Liver Lesions

4.2.1 Pyogenic Abscess

4.2.2 Amebic Abscess

4.2.3 Candidiasis Infection

4.2.4 Echinococcal Cyst

Primary Benign Liver Lesions

Each of the cellular components of the liver - he-patocytes, biliary epithelium and mesenchyme -can give rise to benign tumors.

It is possible to classify these tumors based on their cellular origin:

Hepatocellular Origin

Hepatocellular adenoma Hepatocellular hyperplasia

Focal nodular hyperplasia (FNH) Nodular regenerative hyperplasia

Cholangiocellular Origin

Hepatic cyst

Simple hepatic cyst

Congenital hepatic fibrosis or polycystic liver disease

Mesenchymal Origin

Mesenchymal hamartoma

Hemangioma

Lipoma, Angiomyolipoma, Myelolipoma

Leiomyoma

Most benign tumors are incidental findings during abdominal ultrasonography. The most common entities are simple cysts, cavernous heman-giomas, and focal nodular hyperplasia.

Hemangioma

Hepatic hemangioma is the most common primary liver tumor; the incidence of this lesion in the general population varies in published reports from 0.4% to 20%. Hemangiomas may be multiple in up to 50% of cases, but may also be found in conjunction with other neoplasms. An association with focal nodular hyperplasia occurs in 10-20 % of cases [18,53].

There are two forms of this neoplasm: those that occur in childhood and those that occur in adults. Infantile hepatic hemangioma frequently resolves spontaneously. However, it may also become life-threatening due to arterio-venous shunting and resulting cardiac failure. In such cases, the lesion requires aggressive surgical intervention. Hemangiomas in adults occur most frequently in the fourth and fifth decades of life and there is a much higher incidence in women (about 80%). Estrogen replacement therapy may play a role in the pathogenesis of this type of tumor [24]. Hemorrhage is the most common reason for prophylactic resection, although this occurs relatively infrequently.

Hemangioma, whether solitary or multiple, is a well-defined lesion that ranges in size from a few mm to more than 20 cm. Hemangiomas larger

Fig. 1a, b. Hemangioma on US: ultrasound reveals (a) a well-defined homogeneously hyperechoic lesion (arrow) or (b) a tumor with heterogeneous echogenicity (arrowheads)

Define Hemangioma Ultrasound Image

Fig. 1a, b. Hemangioma on US: ultrasound reveals (a) a well-defined homogeneously hyperechoic lesion (arrow) or (b) a tumor with heterogeneous echogenicity (arrowheads)

Hyperechoic Liver Lesion

Fig. 2. Hemangioma on color Doppler US. On color Doppler ultrasound the lesion demonstrates a homogeneous structure with no flow within the nodule than 10 cm are considered "giant" hemangiomas. Microscopically, they are tumors composed of multiple vascular channels lined by a single layer of endothelial cells supported by a thin, fibrous stroma. Large lesions almost always have a heterogeneous composition with areas of fibrosis, necrosis, cystic changes and intratumoral coarse calcifications. In some cases, abundant fibrous tissue completely replaces the lesion [1,107].

As demonstrated in many studies on the natural history of hemangioma, a large proportion are asymptomatic, and liver function tests are normal. Nevertheless, in some cases, symptoms of liver he-mangioma may be misleading. Rarely, patients present with abdominal pain, and in exceptional cases, with fever, leukocytosis, thrombocytopenia, consumptive coagulopathy (Kasabach-Merritt Syndrome) or cholestasis. Occasionally, very large hemangiomas may cause symptoms by compressing adjacent organs [80].

Fig. 2. Hemangioma on color Doppler US. On color Doppler ultrasound the lesion demonstrates a homogeneous structure with no flow within the nodule

On ultrasound (US) examination, hemangiomas are typically homogeneously hyperechoic with well-defined margins, and may exhibit faint acoustic enhancement. The echogenicity may vary because these tumors may contain cystic and fi-brotic regions; this is especially true in large hemangiomas (Fig. 1). Color Doppler US demonstrates filling vessels in the periphery of the tumor but no significant Color Doppler flow deep within the hemangioma itself (Fig. 2).

Power Doppler, however, may detect flow within hemangiomas but the pattern is non-specific and can also be seen in other primary hepatic liver lesions such as hepatocellular carcinoma (HCC) and focal nodular hyperplasia (FNH) [23].

Contrast-enhanced US allows monitoring of the dynamic enhancement behavior of heman-gioma. During the arterial phase, both capillary and cavernous hemangiomas generally demonstrate an early and strong peripheral enhance-

Lesions Compared Hemangiomas

Fig. 3a-c. Hemangioma on SonoVue-enhanced US. During the arterial phase after contrast administration (a) a large hyperechoic lesion (arrows) id detected and hyperechoic peripheral vessels (arrowheads) are visible. In the portal-venous (b) and equilibrium (c) phases the lesion shows progressive centripetal enhancement, appearing heterogeneously isointense on the equilibrium phase image ment. In the portal-venous phase, hemangiomas show a tendency for centripetal filling, and during the late phase, the vascular components of both capillary and cavernous hemangiomas tend to appear hyperechoic compared to the surrounding normal liver parenchyma. In the late phase, however, cavernous hemangiomas tend to be more heterogeneous due to incomplete filling of the lesion (Fig. 3) [7,56].

Hemangiomas typically appear as low density masses on computed tomography (CT) imaging, with well-defined lobulated margins on unen-hanced scans. During the arterial phase, heman-giomas demonstrate an initial peripheral nodular enhancement on spiral CT; this enhancement is isodense with the the aorta and progresses centrally with time. On delayed scans,the lesion becomes hy-perdense or isodense compared with normal liver parenchyma (Fig. 4). The early nodular peripheral enhancement corresponds to large peripheral feed ing vessels. The presence of nodular enhancement which is isodense with the aorta has been found to be about 70% sensitive and 100% specific in differentiating hemangioma from hepatic metastases [59].Although small lesions often fill-in rapidly and completely (Fig. 5), large tumors may show central non-enhanced areas corresponding to scar tissue, myxoid changes or cystic cavities (Fig. 4) [118].

Hemangiomas are revealed as focal defects on both hepatobiliary and sulfur colloid scans against underlying liver which shows normal isotope uptake. Tagged red blood cell scans can be virtually diagnostic of this lesion; there is a defect in the early phases that shows prolonged and persistent "filling-in" on delayed scans [41].

Evaluation of hemangiomas of the liver is one of the major applications of magnetic resonance (MR) imaging, particularly in oncology patients with atypical hemangiomas detected on CT or US examinations (Fig. 6).

Fig. 4a-d. Cavernous hemangioma. On the unenhanced CT scan (a) the lesion (asterisk) is homogeneously hypodense with well-defined margins. During the arterial phase (b), hyperdense peripheral nodular enhancement is seen, which progresses centrally during the portal-venous phase (c). Stromal components within the lesion are demonstrated during the equilibrium phase (d), as areas of incomplete filling-in (arrow)

Cancer Liver Lesions Mri

Fig. 4a-d. Cavernous hemangioma. On the unenhanced CT scan (a) the lesion (asterisk) is homogeneously hypodense with well-defined margins. During the arterial phase (b), hyperdense peripheral nodular enhancement is seen, which progresses centrally during the portal-venous phase (c). Stromal components within the lesion are demonstrated during the equilibrium phase (d), as areas of incomplete filling-in (arrow)

On unenhanced T1-weighted MR images, hemangiomas are most commonly visualized as well-defined, typically homogeneous, hypointense masses with lobulated borders. On T2-weighted images they characteristically show marked homogeneous hyperintensity with occasional low signal intensity areas corresponding to areas of fibrosis (Fig. 7) [63,92].

After administration of an extracellular Gd-agent, or an agent with both extracellular and liver-specific properties, three types of enhancement pattern may be seen, depending on the size of the lesion. The majority of small lesions under 1.5 cm in diameter show uniform early enhancement during the arterial phase at 25-30 sec post-contrast, or peripheral nodular enhancement progressing cen-tripetally to uniform enhancement in the late arterial and portal-venous phases (Fig. 8).

The second pattern is frequently seen in medium-size lesions between 1.5 and 5 cm, but may also be seen in large hemangiomas. These lesions typically show a peripheral nodular enhancement that progresses centripetally to a uniform enhancement in the equilibrium phase at 3-5 min post-contrast. In particular, large hemangiomas may show peripheral nodular enhancement with persistent central hypointensity corresponding to fibrosis and or cystic areas (Fig. 9).

Peripheral nodular enhancement, in particular, detected during the arterial phase of dynamic MR

Fibrosed Hemangioma

Fig. 5a-d. Hypervascular hemangioma. On the unenhanced CT scan (a) the he-mangioma appears slightly hypodense (arrow). Rapid filling-in is seen in the arterial phase (b), which persists into the portal-venous phase (c). During the delayed phase (d)the hemangioma is isodense with the surrounding liver tissue

Fig. 5a-d. Hypervascular hemangioma. On the unenhanced CT scan (a) the he-mangioma appears slightly hypodense (arrow). Rapid filling-in is seen in the arterial phase (b), which persists into the portal-venous phase (c). During the delayed phase (d)the hemangioma is isodense with the surrounding liver tissue

Mri Scan Lever
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Responses

  • nina
    Is true that benign focal nodular hyerplasia lesion will fall off liver?
    2 years ago

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