Intravascular Lobular Capillary Hemangioma (Intravascular Pyogenic Granuloma): A Clinicopathologic Study of 40 Cases.

Intravascular lobular capillary hemangioma (ILCH), or intravascular pyogenic granuloma, is relatively rare and likely underrecognized. We reviewed all ILCH cases from our institution confirmed pathologically from 2006 to 2019. Immunostains for smooth muscle actin and Wilms tumor 1 were performed on all cases and prior immunohistochemical stains were reviewed. Forty cases were identified (22 females; 18 males) with a median age of 53 years (range: 13 to 85 y). Clinically, all were well-circumscribed, stable to slow-growing raised/cystic skin lesions ranging from 1 to 40 mm. Most were located on the upper extremities (n=18), followed by head and neck (n=16). Vascular lesions were suspected clinically in one third. Of the consultation cases, provided differential diagnoses included Masson tumor, other hemangiomas, and vascular tumors of intermediate malignancy. The common histologic features were a well-circumscribed, lobular proliferation of closely packed capillaries with central ectatic vessels. The surrounding vascular wall was well-visualized in only half of the cases. About 30% of the cases were mitotically active (mean: 8 to 9 mitotic figures/10 HPFs), and 34% showed mild to moderate cytologic atypia. Hobnail features were present in 40% of cases. All cases were diffusely and strongly positive for Wilms tumor 1. Smooth muscle actin stains highlighted pericytes in all cases. Of the 20 cases with clinical follow-up (median: 40 mo), none recurred. ILCH commonly involves the upper extremities and a vascular tumor is suspected clinically in the minority. Mitotic activity and cytologic atypia, when present, can cause confusion with more aggressive vascular tumors. Recognition of this entity is essential as it is a benign lesion with no risk of recurrence following limited local excision.