The objective of this study is to determine the maximal diameter threshold at which infants with lumbosacral, sacrococcygeal, perineal, gluteal, or lower-limb extending infantile hemangiomas should undergo screening for LUMBAR syndrome.

Infantile hemangiomas located in the lumbosacral, sacrococcygeal, perineal, gluteal, or lower-limb-extending regions may be associated with LUMBAR syndrome. LUMBAR syndrome refers to a spectrum of regional congenital anomalies associated with lower-body infantile hemangiomas, including lower-body hemangioma, urogenital anomalies, ulceration, myelopathy or spinal dysraphism, bony deformities, anorectal malformations, arterial anomalies, and renal anomalies.

However, the optimal lesion size threshold for initiating systematic screening remains unclear. In current clinical practice, some patients with large or segmental hemangiomas undergo magnetic resonance imaging and systemic evaluation, whereas others with smaller but potentially high-risk lesions may not be screened. Therefore, a clinically practical and evidence-based diameter threshold is needed to guide LUMBAR syndrome screening.

Previous prospective evidence has suggested that lumbosacral infantile hemangiomas larger than 2.5 cm may be associated with a high rate of spinal anomalies. However, whether this 2.5-cm threshold applies to hemangiomas involving the sacrococcygeal, perineal, gluteal, or lower-limb-extending regions remains uncertain. Therefore, this study aims to prospectively evaluate the relationship between maximal lesion diameter and LUMBAR-associated anomalies and to identify an optimal screening threshold.

Inclusion Criteria:

1. Clinically diagnosed infantile hemangioma.
2. Lesion located in at least one of the following regions: lumbosacral region, sacrococcygeal region, gluteal region, perineal region, perianal region, external genital region, or continuous extension to the lower limb.
3. Maximal lesion diameter ≥2.0 cm.
4. Written informed consent obtained from the parents or legal guardians.

Exclusion Criteria:

1. Vascular anomaly other than infantile hemangioma, such as venous malformation, lymphatic malformation, arteriovenous malformation, or congenital hemangioma.
2. Previously diagnosed genetic or congenital syndrome unrelated to LUMBAR syndrome, which may independently explain the detected anomalies.
3. Incomplete clinical data preventing accurate measurement of lesion diameter.
4. Refusal of participation or refusal to complete core screening examinations.
5. Any condition judged by the investigators to be unsuitable for study participation.

The study population will consist of infants clinically diagnosed with infantile hemangioma involving the lower-body region, including the lumbosacral, sacrococcygeal, gluteal, perineal, perianal, external genital, or continuously extending lower-limb areas. Eligible patients will be prospectively and consecutively recruited from participating centers. The target population is selected because infantile hemangiomas in these anatomical regions, particularly large or segmental lesions, may be associated with LUMBAR syndrome or LUMBAR-associated structural anomalies.

Patients with a maximal lesion diameter of ≥2.0 cm will be included in order to allow evaluation of different candidate screening thresholds. The 2.0-cm cutoff will serve as the enrollment threshold rather than the final screening threshold. This design enables comparison of clinically relevant candidate cutoffs, including ≥2.0 cm, ≥2.5 cm, ≥3.0 cm, ≥4.0 cm, and ≥5.0 cm, for predicting LUMBAR-associated anomalies.