Figure 1: Within the posterior compartment of the left thigh just below the buttocks and
posterior to the hamstrings within the subcutaneous space, there is a 6.5 x 5.5 x 4.5 cm (AP x Cor x CC) mass demonstrating heterogeneous T2 hyperintensity with respect to adjacent muscle. Multiple hypointense linear foci of reticulation are identified throughout the mass with multiple signal flow voids. On gradient echo imaging (not shown) these flow voids were found to represent flowing blood within vessels. These findings result in heterogeneously hyperintense T2 signal.

Figure 2: Image shows a large mass within the posterior compartment of the left thigh which demonstrates T1 isointensity with respect to adjacent muscle. The mass again has multiple areas of hypointense linear foci of reticulation with multiple signal flow voids.

Figure 3: VIBE images demonstrate a large, slightly heterogeneous, enhancing soft tissue mass in the left thigh. There are two large draining veins noted adjacent to this mass (arrows).

Movie 1: There is a large hypervascular mass in the posterior compartment of the left thigh. MRA sequences reveal preferential flow from the abdominal aorta into a dilated left common iliac and left common femoral artery with buckling of the left common iliac artery. The mass is primarily supplied by branches arising from the left profunda femoris artery. The right iliac artery and common femoral artery appear normal in size. There is early filling of an enlarged superficial vein (saphenous system), which subsequently drains into the common femoral vein and left common iliac vein and then into the IVC.

Soft tissue hemangioma.

Hemangiomas are benign vascular neoplasms that closely resemble normal vasculature. They are the most common tumors of infancy and most are medically insignificant. However, some hemangiomas can impinge on vital structures, ulcerate, hemorrhage, incite a consumptive coagulopathy, cause high output cardiac failure, or significant structural abnormalities. Hemangiomas are also a common soft tissue tumor in young adults. Hemangiomas can also occur in extra-cutaneous sites including the liver, gastrointestinal tract, central nervous system, pancreas, gall bladder, thymus, spleen, lymph nodes, lung, urinary bladder, and adrenal glands. Hemangiomas cal also be found as part of one of may of the angiomatous syndromes including: Maffucci syndrome (multiple enchondroma and soft-tissue cavernous hemangioma), Klippel-Trenaunay-Weber disease (cutaneous hemangioma, bone and soft-tissue hypertrophy, and varicose veins), Osler-Weber-Rendu syndrome (hemorrhagic teleangectasia), Kasabach-Merritt syndrome (thrombocytopenia and hemangioma, hemangioendothelioma, or angiosarcoma), and Gorham disease ( massive osteolysis with hemangioma or lymphangioma).

Hemangiomas are classified pathologically by the predominant type of vascular channel and include capillary, cavernous, arteriovenous, or venous types. Capillary hemangiomas are composed of small vessels lined by flattened endothelium. This subtype of hemangioma is the most common soft tissue angiomatous lesion. They are superficially located and can be divided into juvenile, verrucous, and senile varieties. Cavernous hemangiomas are composed of dilated, blood-filled spaces lined by flattened endothelium. These lesions frequently involve the deeper soft tissues, often intramuscular, and do not spontaneously involute. Cavernous hemangiomas often present as masses without other diagnostic features and may require surgical resection. Arteriovenous hemangiomas are considered to be a persistence of a fetal capillary bed, with abnormal communication of arteries and veins. These lesions can be superficial without arteriovenous shunting or deep lesions with arteriovenous shunting that is usually symptomatic (e.g. limb enlargement, distended veins, and reflex bradycardia after compression). These lesions occur in young patients and exclusively involve the soft tissues. Arteriovenous hemangiomas usually have high blood flow, although stenosis and thrombosis can lead to decreased flow. Venous hemangiomas are composed of thick-walled vessels containing muscle and are found in adults. These are generally found in the deep soft tissues such as the reteroperitoneum, mesentery, and muscles of the lower extremities and often have slow blood flow.

MRI is the modality of choice for evaluating soft-tissue hemangiomas and is most often diagnostic. Hemangiomas usually appear as heterogeneous masses on all MR pulse sequences. On T1-weighted images, the intramuscular hemangiomas appear as poorly marginated soft tissue masses. They appear as a low to intermediate signal intensity mass which often contains areas of high signal intensity. The areas of high signal intensity almost always represent areas of fat overgrowth within the mass. Sometimes this fat overgrowth can be so extensive, especially in cavernous hemangiomas, such that portions of it can be indistinguishable from lipoma. On T2-weighted MR images the vascular components of an intramuscular hemangioma usually show marked increased signal intensity while the associated adipose tissue appears isointense to the subcutaneous fat.

The vascular components of a hemangioma often have a characteristic appearance. The vascular channels can appear circular, if seen en face, or have a linear or a serpentine appearance, if visualized longitudinally. These vascular cannels will have either high or low signal intensity depending on the pulse sequence used and the velocity of the blood flow. Intramuscular hemangiomas and their feeding vessels show marked enhancement after administration of intravenous gadolinium contrast. Phleboliths, although more easily recognized on CT or radiographs, appear as circular areas of low signal intensity on all MR pulse sequences not distinguishable from flow voids on contrast enhanced images. Fluid-fluid levels and areas of high signal intensity on T1- and T2-weighted images can represent hemorrhage within the hemangioma.

MR imaging can sometimes also allow differentiation of the various histological subtypes of soft tissue hemangiomas. Cavernous lesions are composed primarily of large cystic spaces while arteriovenous hemangiomas demonstrate prominent serpentine vessels. Arteriovenous hemangiomas may show rapid blood flow in these serpentine vessels which appears as a persistent low signal intensity on all MR pulse sequences. Venous hemangiomas also have serpentine vessels but these vessels show slow blood flow and have a tendency to be oriented along the long axis of extremities and neurovascular bundles. These lesions also tend to be multifocal and have an abundant amount of associated fat.

References:

1. Berquist, TH (ed). MRI of the Musculoskeletal System, 4th Edition. Philadelphia: Lippincott-Williams & Wilkins, c2001. pp. 875-875.
2. Deutsch AL and Mink JH (eds). MRI of the Musculoskeletal System: A Teaching File, 2nd Edition. Philadelphia: Lippincott-Raven Publishers, c1997. pp. 641-642.
3. Murphey MD Fairbairn KJ, Parman LM, et al. Musculoskeletal Angiomatous Lesions: Radiologic-Pathologic Correlation. Radiographics. 1995; 15: 893-917.
4. Antaya, RJ. Infantile Hemangioma. (2002). eMedicine.