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 cut off point. Large facial or lumbar IH warrants investigation for PHACE and LUMBAR syndrome, respectively. Complications of IH include ulceration, obstruction or functional impairment, hypothyroidism, and cosmetic sequelae. Differential diagnoses mostly consist of other vascular tumors and vascular malformations, though IH may sometimes mimic non-vascular tumors or developmental anomalies. Diagnosis is usually clinical and biopsy 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.