Infantile hemangioma. Part 1: Epidemiology, pathogenesis, clinical presentation and assessment.

Infantile hemangioma (IH) is the most common pediatric vascular tumor. Its pathogenesis is poorly understood but thought to represent an aberrant response of pluripotent stem cells to stimuli such as hypoxia and the renin-angiotensin system. IH usually appears during the first few weeks of life and follows a characteristic natural trajectory of proliferation and involution. Their clinical appearance depends on their depth and distribution. Classification comprises superficial, mixed, and deep IH as well as IH with minimal or arrested growth. Multifocal IHs are more likely to be associated with infantile hepatic hemangioma and, although the need for screening based on a specific number of IH has been recently debated, 5 remains the most widely acceptable cutoff point. Large facial IHs warrant investigation for posterior fossa malformations, hemangioma, arterial anomalies, cardiac defects or aortic coarctation and eye anomalies (PHACE) syndrome. Lumbar IHs warrant investigation for lower body IH and other cutaneous defects, urogenital anomalies, ulceration, myelopathy, bony deformity, anorectal malformations, arterial anomalies, and renal anomalies (LUMBAR) syndrome. Complications of IH include ulceration, obstruction or functional impairment, hypothyroidism, and cosmetic sequelae. Differential diagnoses mostly consist of other vascular tumors and vascular malformations, although IH may sometimes mimic nonvascular tumors or developmental anomalies. Diagnosis is usually clinical and biopsy is rarely indicated. High-frequency ultrasonography may help with the differential diagnosis, particularly with subcutaneous lesions. Referral to other specialists may be required in specific cases.