P0890 - Kasabach-Merritt Phenomenon in Kaposiform Hemangioendothelioma: Red Flags in Neonatal Vascular Lesions

Introduction:
Kasabach-Merritt Phenomenon (KMP) is a rare, life-threatening consumptive coagulopathy that occurs in a subset of vascular tumors, namely a benign locally aggressive vascular neoplasm known as kaposiform hemangioendothelioma (KHE) and less frequently in tufted angioma. KMP may occur in as many as 70% of pediatric patients with KHE,1 making it crucial to identify red flag findings in neonatal vascular lesions concerning for KHE.

Case Description:
A 4-month-old female presented to the emergency department for one-day duration of rapidly progressive swelling with violaceous discoloration of her left upper back. History revealed she had 2 discrete bruise-like lesions overlying her left scapula at birth (Figure 1). These lesions remained stable in size throughout the neonatal period and an ultrasound at 2 months of life demonstrated a 5.9 x 2.2 x 5.6 cm, well circumscribed, heterogeneous, hypervascular lesion consistent with hemangioma.

Repeat ultrasound in the emergency department demonstrated interval increase in size of a heterogeneous vascular tumor with ill-defined borders. Due to rapid progression and changing radiographic findings, laboratory evaluation was obtained and demonstrated severe thrombocytopenia (platelets 9,000/μL) and findings suggestive of DIC (fibrinogen 150 mg/dL, d-dimer >20 μg/mL, INR 1.2). Suspicion for KHE complicated by KMP was raised and MRI with contrast confirmed a vascular mass that was infiltrating through multiple tissue planes consistent with KHE (Figure 2).

Treatment was initiated with sirolimus 0.8 mg/m2 BID (goal sirolimus level 8-10 u/dl) and prednisolone 2 mg/kg/d divided BID. Within 2 weeks, family noted significant improvement in localized swelling, while blood work confirmed normalization of platelet count (450,000/μL) and normalized coagulation pathway.

Discussion/

Conclusion:
This case illustrates the importance of understanding the natural history and clinical findings of neonatal vascular tumors. The most common neonatal vascular tumor is infantile hemangioma. These tumors are typically not fully formed at birth, proliferate during the first several months of life, and are generally not associated with significant morbidity. Clinical characteristics inconsistent with this history may signify the presence of a more serious vascular tumor like KHE.

The misdiagnosis of an infantile hemangioma could have been avoided in our patient if red flag clinical findings of the tumor quality (deep bruise-like swelling) and natural history (being fully formed at birth and remaining visually unchanged at 2 months of life) were able to call into question the initial ultrasound results. The secondary presentation illustrated successful identification of clinical red flags (acute tumor enlargement and ill-defined tumor borders on imaging) to avoid anchoring bias and prompt diagnostic re-evaluation with subsequent early treatment. Pharmacologic management of KHE, in particular with sirolimus, has shown promising rapid response in the treatment of KMP as well as overall tumor regression,2 thus reinforcing the importance of prompt KHE diagnosis.