Challenges and limitations in the pathological application of the ISSVA 2025 classification of vascular anomalies: A 5-year retrospective study

Vascular anomalies encompass a heterogeneous spectrum of tumors and malformations where accurate classification is essential for appropriate clinical management. The International Society for the Study of Vascular Anomalies (ISSVA) 2025 classification represents the contemporary global standard for vascular lesions however; antiquated and biologically imprecise terminology continues to pervade in routine diagnostic practice. In this retrospective study, 164 biopsy-proven vascular anomalies diagnosed between January 2018, and December 2023 were reviewed and reclassified according to ISSVA 2025 criteria based on morphology, special stains, and immunohistochemistry where indicated. Reclassification was required in 96 cases (58.53%), confirming substantial discordance between prevailing terminology and current standards. Vascular malformations were the predominant lesions (67.7%) and required reclassification in majority of cases (88.5%) with venous malformations being the most frequent category that were reassigned. The term ‘cavernous hemangioma’ emerged as the single most frequent source of diagnostic error (n = 28), contributing to 50% reclassification to venous malformation. Vascular tumors comprised 51 cases (31.1%), of which 9 (17.6%) were reclassified to various other entities. Five cases were reassigned to intramuscular fast-flow vascular anomaly which is a newly delineated entity in the ISSVA 2025 classification. GLUT-1 immunohistochemistry was performed in six cases where distinction between infantile and congenital hemangioma subtypes was required based on histomorphology. The challenges observed were the continued use of outdated terminology, limited availability of imaging studies to aid in classifying fast and slow-flow lesions, and lack of molecular diagnostic platforms posing significant barriers to the systematic adoption of ISSVA 2025 in resource-limited settings.