Clinical Characteristics

Hemangioma of infancy is a benign proliferation of blood vessels that occurs in approximately 5% of the newborn population, with a reported incidence as high as 10% in the first year of life, making it one of the most common tumors of infancy. ^{2 ,​ 3 ,​ 4} This discrete and generally well-circumscribed tumor predominantly affects females, persons of fairer skin types, and premature infants (particularly those weighing < 1,500 g) ( Fig. 3.1 ). ⁵ The clinical presentation is variable, depending largely on the anatomical site and the level of cutaneous involvement. More than half of these lesions tend to involve the head, neck, and trunk, and lesions can occur either singly or in multiple anatomical sites.

Based on these clinical features and the level of soft tissue involvement, these lesions have traditionally been described as superficial, deep, or combined. Further efforts to better characterize these lesions have involved using anatomical spatial configurations (i.e., localized, segmental, indeterminate, or multifocal). There is some debate as to whether hemangiomas that are called “segmental type” are a misnomer because, instead of being limited to a particular anatomical location, they may in fact be derived embryologically from a soft tissue segment. ⁶ Despite greater than approximately 50% of hemangiomas having good outcomes, it appears the segmental type of hemangiomas have higher rates of complications, usually resulting in ulceration. ⁵ Additionally, segmental hemangiomas and hemangiomas with a deep component tend to have an unusually prolonged growth phase. ⁷ Other epidemiologic studies have found that, in addition to gender, ethnicity, and early gestational age, certain prenatal associations also exist, including older maternal age, placenta previa, and pre-eclampsia. ⁸

Although the pathogenesis is not completely understood, the natural history of these tumors is well established. IHs can be present at birth or develop postnatally, typically manifesting at a median age of 2 weeks. Approximately a third of these lesions will manifest as precursor or nascent lesions, either as an erythematous macule or blanched lesion, with or without telangiectasias. ⁹ Over a span of months during the initial period of rapid growth, these lesions continue to develop and enlarge, reaching their maximum size after 3 to 6 months. ^{2 ,​ 3} A recent prospective study of the growth characteristics of IHs found that the early proliferative part of the growth phase was essentially complete by 5 months of age and the overall growth was complete by 9 months of age. ¹⁰ Most of the time, this period of growth is followed by a slower period of total or partial regression of the lesion, occurring at as late as 5 to 10 years of age. ^{2 ,​ 4} Finally, the end stage of this lesion occurs when the involution of the lesion is replaced, either entirely or partially, by a fibrofatty residuum. ¹¹

In addition to the previously classified types of hemangiomas, several atypical presentations of hemangiomas can occur, including deep subcutaneous, telangiectatic, AVM-like, multiple cutaneous, and congenital hemangiomas. ¹² In addition, it is important for treating clinicians to keep in mind that mimics of hemangiomas do exist. The differential diagnosis includes capillary malformations (CMs) or telangiectasias, venous and lymphatic vascular malformations, KHE, TAs, pyogenic granulomas, infantile hemangiopericytomas, spindle cell hemangioendotheliomas, congenital eccrine angiomatous hamartomas, congenital fibrosarcomas, and other deep soft tissue masses. ¹²

Pathogenesis

Historically, the pathogenesis of IHs has been difficult to elucidate. Fortunately, attempts at understanding vasculogenesis and angiogenesis of normal and malignant vascular development has contributed to much of what we now know about hemangiomas. ¹³ Also, recent investigations of hemangiomas during different phases of the growth cycle and during involution have revealed some useful information regarding cellular markers ( Table 3.3 ).

Studies have shown that during the proliferative phase, expression of type IV collagenase, vascular endothelial growth factor (VEGF), and basic fibroblast growth factor (bFGF) increase, in contrast to the markedly decreased expression of VEGF observed during involution of the hemangiomas. During involution, a persistently high expression of bFGF exists despite the decreased expression of VEGF. Other studies have revealed that during the proliferative phase, VEGF increases proangiogenic factors (e.g., B-cell lymphoma-2, interleukin-8) while decreasing levels of the apoptotic enzyme (caspase-3), ¹⁴ whereas expression of apoptotic proteins increases in involuting hemangiomas. ¹⁵ In addition, gene-expression analysis has shown that insulin-like growth factor 2 follows an expression pattern similar to that of VEGF, increasing during proliferation and significantly decreasing during involution. Recent studies have shown that IH endothelial cells have low VEGF receptor (FEGFR)1 expression but constitutive VEGFR2 signaling caused by reduced activity of a pathway involving β1 integrin, the integrin-like receptor tumor endothelial marker-8 (TEM-8), VEGFR2, and nuclear factor of activated T-cells (NFAT). ¹⁶ Mutations in VEGFR2 and TEM-8 genes have also been found in some patients with IHs and caused reduced NFAT activity and VEGFR1 expression.

Other efforts toward examining messenger RNA expression patterns of genes necessary for angiogenesis in hemangiomas have shown that the angiopoietin-Tie-2 system is also a molecular regulator of IHs. ¹⁷ Numerous studies evaluating immune-mediated processes and their roles in IH involution have been fruitful. For instance, one study showed how treatment with imiquimod for proliferating hemangiomas accelerated their regression. ¹⁸ This finding was further examined in murine studies assessing the effects of imiquimod and the expression of tissue inhibitor of matrix metalloproteinase 1 (TIMP-1), ¹⁹ which is significant because this inhibitor (i.e., TIMP-1) is known to be increased in involuting hemangiomas. ²⁰ Continuing this effort to understand more fully the involvement of the immune system with IHs, another group investigated the role of indoleamine 2,3 dioxygenase (IDO). ²¹ IDO is an enzyme that is involved in the degradation of the amino acid tryptophan. Tryptophan’s availability is critical to normal T-cell functioning. When tryptophan is depleted or decreased, T-cell proliferation and activity decrease and T-cell apoptosis increases. Ritter et al proposed that the extended involution period of IHs is secondary to the early inhibition of T-cell function by way of increased levels of IDO. They found that IDO levels were highest during the proliferative phase of IHs and lowest during involution. ²¹

More recently, several distinct and shared markers between IH and placental fetal microvessels have been demonstrated. These cellular markers include glucose transporter 1 (GLUT1), Lewis Y antigen, Fc (Fragment, crystallizable region of heavy chain regions of immunoglobins) gamma receptor II, and merosin. ^{11 ,​ 22} These findings raise the possibility that angioblasts (vascular precursor cells) might undergo aberrant differentiation into a placental vascular phenotype during development. ²³ Another consideration is that placental vascular cells shed, secondary to local trauma, and embolize to locations (via right-to-left shunting) within the fetus and then undergo maturation to become a hemangioma. This notion is further supported, but yet to be proven, by the observed increased incidence of infants born with hemangiomas of mothers who have undergone chorionic villous sampling during pregnancy. ²⁴ Additionally, an immunohistochemical evaluation of the expression of vascular lineage-specific markers revealed ( Fig. 3.2 ) that IHs express the same markers [specifically, CD34 and lymphatic vessel endothelial hyaluronan-1 (LYVE-1)] as the cardinal vein during early normal embryogenesis, suggesting that IHs display the immature immunophenotype of a vessel arrested early in vascular differentiation. ²⁵

Lastly, the significance of mast cells and their proangiogenic role in hemangiomas has yet to be fully understood. Recent efforts have found that the number of mast cells is highest during the involuting phase, second highest once the hemangioma has completely involuted, and lowest during proliferation. ^{26 ,​ 27} Other studies have supported this relationship by studying how mast cell proliferation increases during the involuting stage of IH. ²⁷ Subsequent investigations have revealed that, of the several mast cell mediators, VEGF and FGF-2 are the most potent of the angiogenic factors. ²⁸

Histology

Both focal and segmental types of IHs have a characteristic histopathologic ( Fig. 3.1 c,d) evolution that correlates with the gross clinical appearance. During the proliferative phase, hemangiomas are composed of lobules of compact capillaries lined by plump, mitotically active endothelial cells with intervening stromal elements (fibroblasts, pericytes, and mast cells). Difficult to appreciate in early proliferation are small vascular lumens noted focally throughout the growing lesion. To illustrate more clearly the individual lobules, reticulin and periodic-acid Schiff stains can be used to highlight the reticulin fibers surrounding the endothelial cells and underlying endothelial cell basement membrane, respectively. As the proliferating lobules mature, the fibrous septae separating each lobule become more apparent. It is within these septae that large feeding and draining vessels can be found. The mitotic activity during this stage is reflective of the hyperplastic nature of IHs. Notably, increased numbers of mast cells are seen at this stage. Once the lesion has reached maturity, it then begins the next stage of involution.

At the beginning of involution, mitotic activity decreases and the numbers of mast cells increase somewhat; the ensuing apoptosis of the endothelium results in a flattened endothelial appearance. During this stage, the numbers of vessels begin to decrease and those that remain undergo separation and replacement by fibrofatty tissue. Toward the end stages of involution, the numbers of mast cells begin to decrease along with the numbers of persistent lobules. In addition to the morphologic findings, immunohistochemical stains can further assist in differentiating IHs from the other vascular lesions. Of these markers, GLUT1 is the most specific for IHs ( Fig. 3.1 e). In IHs, GLUT1 stains strongly positive but negative in congenital hemangiomas, vascular malformations, and other various reactive vascular lesions.

Clinical Characteristics

Clinically, RICHs ( Fig. 3.3 a,b,c) can manifest as infiltrating violaceous plaques or firm violaceous telangiectatic nodules with a surrounding pale halo and large peripheral radiating vessels. These lesions can also have a central depression, scar, or ulceration. Prenatal ultrasounds have detected them at as early as 12 weeks of gestation, and they typically spontaneously involute by the time the child is 14 months of age or sooner. ³¹ The early flow dynamics of these tumors by ultrasound or MRI is fast flow. It is important not to confuse RICHs with congenital fibrosarcomas on imaging. ³² Classically, RICHs demonstrate accelerated involution by 12 to 14 months of age. ⁹ The remaining skin overlying the regressed lesion is often depressed or atrophic. Subsequent Doppler imaging of the postregressional lesion reveals normal blood flow.

Pathogenesis

The pathogenesis of RICHs is still unclear and it is uncertain whether there is any similarity to that of IHs.

Histology

Compared with the lobular architecture of IHs and NICHs, RICHs tend to have the smallest lobules ( Fig. 3.3 d,e). The endothelial cells are moderately enlarged and occasionally may have cytoplasmic endothelial inclusions. Similar to NICH, RICHs have prominent draining channels; however, RICHs tend to have more perilobular fibrous tissue than NICHs and much more than IHs. In resected lesions, a zonation effect is observed. This effect is created by the central portion of the RICHs having more involution than the periphery. The zonation effect can also be seen in NICHs but not in IH. Unlike IHs, RICHs characteristically do not stain immunohistochemically ( Fig. 3.3 f) for GLUT1. ²⁹

Clinical Characteristics

Clinically, NICHs can appear much like RICHs ( Fig. 3.4 a). Characteristically, NICHs have coarse, prominent, overlying telangiectasias with admixed areas of pallor and a pale peripheral halo. Usually, they are warm to palpation, are only slightly raised, and have a heterogeneous pink–purple color. These lesions tend to occur slightly more often in male infants, and they grow proportionally with the child. Hemodynamically, these lesions are quite similar to IHs during the proliferative phase, exhibiting fast-flow dynamics by Doppler examination. ^{29 ,​ 33 ,​ 34} Some propose that NICHs could be a variant of RICHs, as some RICHs have been observed to involute only partially, resembling an NICH. ^{12 ,​ 35}

Pathogenesis

The pathogenesis of NICHs is still unclear, and it is uncertain whether there is any similarity to IHs or RICHs.

Histology

The architecture of NICHs ( Fig. 3.4 b,c) is generally dominated by large lobules of small, thin-walled vessels with curved lamina and a large, often stellate, central vessel. ²⁹ They also have hobnailed endothelial cells and eosinophilic endothelial cytoplasmic inclusions with prominent lobular draining channels and a prominent interlobular vascular network. ³⁴ Similar to the involuting or involuted phase of IHs, NICHs can have lobules of capillaries with multilamellated basement membranes. ²⁹ However, extensive fibrosis separates the lobules. An interesting aspect is the presence of iron scattered apparently free and in siderophages diffusely throughout the tissue. Another characteristic feature is the presence of extramedullary hematopoiesis. Generally, there is no significant atypia. Like RICHs, these lesions are negative for GLUT1.

Clinical Characteristics

Despite a small number of cases of infants with facial hemangiomas and associated aortic or cerebrovascular malformations reported in the literature in the 1980s, Frieden et al were the first to describe the PHACES association or syndrome. ^{36 ,​ 37} The PHACES association ( Fig. 3.5 ) is a neurocutaneous syndrome associated with facial segmental IHs consisting of the following features: posterior fossa brain malformations, cervicofacial hemangiomas, arterial anomalies, cardiac defects or coarctation of the aorta, eye anomalies, and sternal clefting or supraumbilical raphe. ^{36 ,​ 38} Although up to 70% of the patients have only one extracutaneous defect, the most critical and important associations remain the cardiac and cerebrovascular anomalies.

It is likely that PHACES is an underrecognized syndrome given that nearly 20% of the infants who are referred for facial hemangiomas are eventually diagnosed with this disorder. ³⁹ Most infants with PHACES have hemangiomas in the V1 distribution alone or in combination with V2, V3 dermatomes. They have a tendency to be ipsilateral and more commonly are on the left side of the face; however, bilateral lesions can occur. The more extensive the cutaneous disease, the more likely there seems to be structural or vascular central nervous system involvement, resulting in higher complication rates. ⁴⁰ The most frequent cardiovascular anomaly associated with PHACES is aortic coarctation. These coarctations tend to have an absence of aortic valve pathology and a much more complex anatomical involvement than the classic aortic coarctation. ⁴¹

The noncutaneous associations of PHACES are described in order of most to least common. Beginning with the posterior fossa abnormalities, the different types of abnormalities include Dandy-Walker malformation, hypoplasia or absence of cerebellum, corpus callosum of cerebrum or the septum pellucidum, frontal lobe calcifications, microcephaly, and arachnoid cysts. Of the arterial malformations, arterial stenosis and intracranial aneurysmal dilations are most common. Arterial vessel absence, or hypoplasia, as well as anomalous or aberrant branches of carotid and vertebral arteries can occur. The persistence of embryonic arteries should also be considered. As previously mentioned, aortic coarctations are the most common of the aortic cardiac anomalies, followed by, aneurysms, hypoplasia, atresia, duplication, and aberrant locations. Aside from the aortic complications, pulmonary stenosis, patency of both ductus arteriosus and foramen ovales can occur, as well as ventricular or atrial septal defects and aortic and tricuspid atresia. Ophthalmologic abnormalities can include microphthalmos, exophthalmos, coloboma, optic nerve atrophy or hypoplasia, hemangiomas, congenital cataracts, congenital glaucoma, amblyopia, and strabismus. Sternal fusion defects, including supraumbilical raphes, sternal clefting and a sternal pit have been described. ⁴²