![[From the Archives of the AFIP main menu]](../../../../../buttons/afipbtt2.gif){kind=small}
![[HOME]](../../../../../buttons/afiphom3.gif){kind=small}
RadioGraphics
Hemangiomas are classified pathologically by the predominant type of vascular channel (capillary, cavernous, arteriovenous, or venous) seen at histologic examination (Figure 1). Nonvascular components can also be seen in angiomatous lesions, particularly cavernous hemangioma, including fat, smooth muscle, fibrous tissue, bone, hemosiderin, and thrombus. Overgrowth of adipose tissue is most frequently associated with hemangiomas, and this characteristic led some authors in the past to refer to these lesions as angiolipomas. However, fat overgrowth should be considered a reactive phenomenon as opposed to a true neoplastic component; therefore, the term angiolipoma is not appropriate for the vast majority of these musculoskeletal vascular lesions (1,2,3). True angiolipomas are rare lesions of the subcutaneous tissue, most commonly in the forearm, and imaging of this neoplasm has not been reported to the best of our knowledge.
Capillary hemangiomas are composed of small vessels lined by flattened endothelium. Overall, this subtype is the most common soft-tissue angiomatous lesion, often being divided into juvenile, verrucous, and senile varieties. However, it is infrequently evaluated radiologically because these lesions most commonly involve the skin and subcutaneous tissue. Capillary hemangiomas usually occur in the first few years of life. The juvenile capillary hemangioma (strawberry nevus) occurs in one of every 200 births, is multiple in 20% of the cases, and involutes by age 7 years in 75% 90% of the cases (4). Osseous capillary hemangiomas are most frequently found in the vertebral body (5).
Cavernous hemangiomas are composed of dilated, blood-filled spaces lined by flattened endothelium and overall are less common than capillary lesions. However, these angiomatous lesions are encountered more often by radiologists for two reasons. First, cavernous hemangiomas frequently involve the deeper, often intramuscular, soft tissues and manifest clinically as masses without other diagnostic features. Second, unlike capillary hemangiomas, they do not involute and may require surgical resection. Young children are usually affected, and calcification may be present, typically in the form of dystrophic mineralization in an organizing thrombus (phlebolith). Cavernous hemangiomas in bone most frequently involve the calvaria (1).
Arteriovenous hemangiomas can be considered a persistence of the fetal capillary bed, with abnormal communication of the arteries and veins (6,7). These lesions occur in two forms: (a) superficial lesions without arteriovenous shunting that are usually clinically insignificant and (b) deep lesions with arteriovenous shunting that are frequently symptomatic. Arteriovenous hemangiomas occur in young patients and almost exclusively involve the soft tissues. These lesions usually have high blood flow, although stenosis and thrombosis can lead to decreased flow (6,7). High-flow lesions may produce symptoms similar to those accompanying a vascular shunt, including limb enlargement, distended veins, bruit, overlying skin warmth, and reflex bradycardia after compression (Branham sign). Some investigators consider these lesions to be congenital arteriovenous malformations (8). For the purposes of our discussion, however, we prefer to classify these lesions as hemangiomas (ie, composed of increased numbers of normal or abnormal arteries and veins) (1,8,9).
Venous hemangiomas are composed of thick-walled vessels containing muscle and rarely involve the musculoskeletal system. These lesions are generally found in adults and most frequently are located in the deep soft tissues such as the retroperitoneum, mesentery, and muscles of the lower extremities. They often have slow blood flow, and phleboliths may be present.
Osseous Hemangioma
The majority of hemangiomas that involve bone are discovered incidentally in asymptomatic patients. Men are affected twice as often as women, and lesions are usually discovered in the 4th 5th decades of life. Soft-tissue components may also be associated with these lesions. Osseous hemangioma is particularly common in the spine and calvaria and less frequently affects long bones such as the tibia, femur, and humerus.
Vertebral hemangioma is extraordinarily common, seen in 11% of the cases in one large autopsy series (10). It accounts for 28% of all skeletal hemangiomas (11). These lesions can involve only a portion of or the entire vertebral body and are multiple in one-third of the cases (12). The thoracic spine is the most common location for vertebral hemangiomas (Figure 2) (5,10,11,12).
At radiography, vertebral hemangiomas classically have a coarse, vertical, trabecular pattern, with osseous reinforcement (trabecular thickening) adjacent to the vascular channels that have caused bone resorption (13). This appearance on radiographs represents a response to stress and has been likened to corduroy. Vertebral fractures at the site of these hemangiomas are unusual because of this trabecular reinforcement. At CT, the thickened trabeculae are seen in cross section as small punctate areas of sclerosis, often called the polka-dot appearance. At MR imaging, areas of trabecular thickening have low signal intensity, regardless of the pulse sequence used (Figure 3). On T1-weighted MR images, the signal intensity of vertebral hemangiomas varies from low to high, depending on the degree of adipose tissue present (Figure 3). T2-weighted MR images usually show areas of very high intensity corresponding to the vascular components (14). CT or MR images obtained after intravenous administration of contrast material demonstrate lesion enhancement.
Vertebral hemangiomas occasionally cause neurologic symptoms from spinal cord compression, particularly if these lesions extend into the posterior elements or surrounding soft tissues, expand bone, or fractureAu: this seems to contradict the preceding paragraph, in which you indicated that fracture was unusual; please address discrepancy* (Figure 4) (5,14,15). The larger the degree of fat overgrowth in the stroma between thickened trabeculae (seen on CT images as low attenuation between thickened trabeculae and as areas of high intensity on T1-weighted images and intermediate intensity on T2-weighted images), the less likely these lesions will be symptomatic (inactive hemangioma) as shown by Laredo and coworkers (15).
Calvarial hemangiomas account for 20% of all hemangiomas and are most frequent in the frontal or parietal region (11). These lesions arise in the diploic space and cause expansion that often involves the outer table to a greater extent. At radiography and CT, a calvarial hemangioma commonly appears as a lytic lesion with a pattern of radiating, weblike or spoke-wheel, trabecular thickening (Figure 5) (5,10,11). This characteristic appearance, as in vertebral lesions, is caused by preexisting trabeculae that have become thickened through intramembranous bone formation adjacent to the angiomatous channels. Recognition of the pattern should alert the radiologist to the vascular nature of the lesion.
Osseous hemangiomas in other locations may also have radiating trabecular thickening on radiographs. Another common pattern is a bubbly bone lysis that creates a honeycomb, latticelike, or "hole-within-hole" appearance. These lytic areas are invariably multifocal and usually metaphyseal or epiphyseal. Bone lysis can have linear and circular components on radiographs, suggestive of a vascular lesion, with linear and circular elements representing vascular channels seen longitudinally and en face, respectively. However, these serpentine vascular channels are recognized more easily with CT and MR imaging. Characteristically, these channels have low signal intensity on T1-weighted images and very high signal intensity on T2-weighted images because of slow blood flow. In arteriovenous lesions with faster blood flow, low signal intensity may persist with all MR imaging pulse sequences. The appearance of osseous hemangiomas at bone and red blood cell labeled scintigraphy is variable, from photopenia to moderate increased activity (16,17).
Periosteal or cortical hemangiomas occur most frequently in the anterior tibial diaphysis. These lytic cortical lesions may also show the characteristic multifocal vascular channels (Figure 6) or be seen as a larger, nonspecific region of bone destruction. Cortical hemangiomas may predispose the bone to fracture, and periosteal reaction may accompany these lesions.
Soft-Tissue Hemangioma
Hemangioma is one of the most common soft-tissue tumors, constituting 7% of all benign tumors (7). It is the most frequent tumor of infancy and childhood (1,7). Clinically, these lesions often intermittently change in size and are painful; rarely, the overlying skin may have a characteristic bluish discoloration. Soft-tissue hemangiomas are more common in women and may dramatically increase in size during pregnancy. These tumors may be superficial or deep, and deeply seated lesions are more frequently a diagnostic dilemma, leading to radiologic assessment. They are usually intramuscular, although synovial hemangiomas (less than 1% of hemangiomas) also occur (1).
At radiography, soft-tissue hemangiomas may not be visualized or may appear only as a nonspecific soft-tissue mass. Characteristic calcifications with phleboliths occur most frequently in cavernous hemangiomas (30% of lesions) but may also be seen with other angiomatous lesions (Figure 7) (7,18,19). Nonspecific curvilinear or amorphous calcification may also be seen. Soft-tissue hemangiomas may extend directly into bone, or bone overgrowth (longitudinal and axial) may occur secondarily because of chronic hyperemia (Figure 8). Synovial hemangioma may cause repetitive bleeding into the joint, resulting in a radiographic appearance identical to that of hemophilic arthropathy, although the former is almost exclusively monoarticular (20,21). The knee is involved in 60% of cases, and the elbow is involved in 30% of cases (22).
At CT, a soft-tissue hemangioma is seen as a soft-tissue mass in which serpentine vascular components may enhance after administration of contrast material (23,24,25,26). Associated fat overgrowth may also be seen (Figure 9); however, both of these features are better demonstrated with MR imaging. Phleboliths are well seen with CT (Figure 9).
Sonography of soft-tissue hemangiomas often reveals a complex mass (27). Acoustic shadowing may be caused by phleboliths if they are large enough. In some cases, Doppler US studies reveal lesions with abnormal low-resistance arterial signal with forward flow during both systole and diastole, findings indicating low vascular resistance (25,26,27).
MR imaging is considered the best modality for evaluating most soft-tissue masses, and hemangioma is no exception (28,29,30). For angiomatous lesions, MR imaging findings are frequently diagnostic (31,32,33,34,35,36). On T1-weighted images, a hemangioma appears as a low- to intermediate-signal-intensity mass, which may also contain areas of high signal intensity, a finding that some have attributed to slow-flowing blood. In our experience, however, this high signal intensity is almost invariably due to fat overgrowth, and it often predominates peripherally within the mass, extending into septations (Figure 7). In fact, lipomatous overgrowth in cavernous hemangiomas can be so extensive that some areas within these lesions are histologically indistinguishable from a lipoma (7). On T2-weighted images, a hemangioma shows areas that are very high signal intensity due to vascular tissue and other regions that are intermediate in signal intensity (isointense relative to subcutaneous fat) due to fat (Figure 7). Hemangiomas are thus often heterogeneous on both T1- and T2-weighted MR images, although cavernous lesions smaller than 2 cm in size have been reported to be homogeneous (18). In one study, the ratio of signal intensity measurements on T2-weighted images (repetition time of 2,000 msec and echo time of 90 msec at 1.0 T) of hemangioma to skeletal muscle was greater than seven, distinguishing it from other soft-tissue masses (18). The vascular channels and spaces of hemangioma frequently have a characteristic circular (seen en face) or linear or serpentine (seen longitudinally) appearance with either high or low signal intensity, depending on the pulse sequence used and the rapidity of blood flow (Figure 7, Figure 8). Both the hemangioma and feeding vessels from the surrounding soft tissue enhance after intravenous administration of gadolinium (Figure 7) (25). Phleboliths appear as circular areas of low signal intensity. Areas of hemorrhage may be recognized by their high signal intensity on T1- and T2-weighted images and fluid-fluid levels (37).
MR imaging may at times allow differentiation between arteriovenous and cavernous hemangiomas. Lesions composed primarily of large cystic spaces are cavernous, whereas arteriovenous hemangiomas show more prominent serpentine vessels. Faster flow may also be recognized in arteriovenous hemangiomas as areas of low signal intensity on all MR images (Figure 8). Venous hemangiomas, on the other hand, show slow-flow serpentine vessels, as well as a tendency to be oriented along the long axis of the extremities (78% of cases) and neurovascular bundle (64%) and to have multifocal involvement (37%) and muscle atrophy with increased subcutaneous fat (36).
Dynamic, blood pool, and static bone scintigraphic studies often show only mildly increased activity in hemangiomas. These changes are related to increased blood flow, alterations of capillary permeability, and calcification. Soft-tissue hemangiomas may also show accumulation of technetium-99m diethylenetriaminepentaacetic acid or radiotracer-labeled red blood cells, reflecting vascular flow and the blood pool to the lesion (14,15,38,39).
Findings at angiography are variable, depending on the type of hemangioma. Capillary and cavernous hemangiomas have enlarged arteries with pooling of contrast material and arteriovenous shunting (9). Arteriovenous hemangiomas have large, tortuous feeding arteries; early draining veins; and dense staining. On the other hand, venous lesions may appear normal at arteriography and require venography or direct puncture with injection of contrast material for detection (Figure 10) (40).
Hemangioma