Intravascular papillary endothelial hyperplasia presenting as a lytic frontal bone lesion in a pediatric male.

Background: Masson tumor, also known as intravascular papillary endothelial hyperplasia (IPEH), is a benign reactive proliferation of endothelial cells that may present in various places in the body, most commonly in the head-and-neck region. It is more common in adolescents and adults and rarely presents as a lytic skull lesion in the pediatric population. Case Description: A 10-year-old right-handed previously healthy male presented with a painless, firm, gradually enlarging swelling over the right frontal scalp for 2 months but was otherwise neurologically intact. Computed tomography scan of the brain showed a lytic lesion in the right frontal bone with an enhancing soft-tissue component and a small dural/extradural extension and with no intracranial abnormality. Differential diagnoses included Langerhans cell histiocytosis (LCH) and, less likely, sarcoma. The patient underwent right frontal craniectomy with complete excision of the lytic lesion and cranioplasty reconstruction. Histopathology revealed papillary endothelial proliferation within a vascular lumen with positive reticulin staining, consistent with IPEH (Masson's tumor), without malignant features. Conclusion: IPEH is a rare benign vascular lesion that may present as an osteolytic skull lesion, even in pediatric patients, and may be radiologically mistaken for more common or aggressive lesions such as osteosarcoma, Ewing's sarcoma, or LCH, requiring histological analysis for confirmation. It should be considered in the differential diagnosis of pediatric lytic skull lesions, and complete gross total resection is typically curative.