Pathology International 2005; 55: 391–397 Blackwell Science, LtdOxford, UKPINPathology International1320-54632005 Japanese Society of PathologyJuly 2005557391397Original Article Pyogenic granulomaA. Epivatianos et al. Correspondence: Apostolos Epivatianos, DDS, PhD, Department of Oral Medicine and Oral Pathology, School of Dentistry, University of Thessaloniki, Thessaloniki 54124, Greece. Email: aepivati@dent.auth.gr Received 13 January 2005. Accepted for publication 25 February 2005. Original Article Pyogenic granuloma of the oral cavity: Comparative study of its clinicopathological and immunohistochemical features Apostolos Epivatianos, 1 Demetrios Antoniades, 1 Thomas Zaraboukas, 2 Eleni Zairi, 3 Athanasios Poulopoulos, 1 Athina Kiziridou 4 and Savas Iordanidis 5 1 Department of Oral Medicine and Oral Pathology, School of Dentistry, 2 Department of Pathology, School of Medicine and 5 Department of Oral and Maxillofacial Surgery, Dental School, University of Thessaloniki, 3 Interbalkan Hospital of Thessaloniki and 4 Anticancer Hospital of Thessaloniki, Thessaloniki, Greece There are two histological types of pyogenic granuloma (PG) of the oral cavity: the lobular capillary hemangioma (LCH) and non-LCH type. The aim of the present study was to examine and compare the clinical features, etiological factors, diameter of vascular elements and immunohis- tochemical features of LCH and non-LCH histological types of PG to determine whether they are two distinct entities. Thirty cases of LCH and 26 cases of non-LCH PG were retrieved and retrospectively studied. Clinically, LCH PG occurred more frequently (66.4%) as sessile lesion whereas non-LCH PG occurred as pedunculated (77%). Non-LCH PG was associated more frequently (86.4%) with etiological fac- tors. The lobular area of the LCH PG contained a greater number of blood vessels with small luminal diameter than did the central area of non-LCH PG. In the central area of non-LCH PG a significantly greater number of vessels with perivascular mesenchymal cells non-reactive for a-smooth muscle actin and muscle-specific actin was present than in the lobular area of LCH PG. The differences found in the present study suggest that the two histological types of PG represent distinct entities. Key words: a-smooth muscle actin, CD34, lobular capillary hemangioma, muscle-specific actin, pyogenic granuloma Pyogenic granuloma (PG) is a common vascular growth of the skin and mucous membranes. Clinically oral PG is char- acterized as a soft mass, smooth or lobulated, sessile or pedunculated. The color of the lesion ranges from pink to red purple and hemorrhage may occur either spontaneously or after minor trauma. 1 The term ‘pyogenic granuloma’ or ‘gran- uloma pyogenicum’ was applied by Hartzell 2 and is a misno- mer in that, contrary to what the name implies, the lesion does not contain pus. There are two histological types of PG. The first type con- sists of highly vascular proliferation that resembles granula- tion tissue, 1,3 whereas the second type is characterized by proliferating blood vessels that are organized in lobular aggregates although superficially the lesion frequently under- goes no specific change, including edema, capillaries dilation or inflammatory granulation tissue reaction. This histological type of PG was called lobular capillary hemangioma (LCH) 4 and the lobular arrangement of blood vessels is required by some pathologist for the diagnosis of PG. 1,5,6 ‘Epulis granu- lomatosa’ is a term used to describe hyperplastic growth of granulation tissue that sometimes arises in healing extraction sockets and is considered special PG. 1,3 Many previous clinicopathological studies of PG included cases of both LCH and non-LCH histological type, 7–12 others examined only cases with LCH histological type 13–15 and others with non-LCH type. 16,17 To the best of our knowledge, the clinical features and etiological factors of the two histological types of PG have not been studied comparatively in the literature. The aim of the present study was to examine and compare the clinical features, etiological factors, diameter of vascular elements and immunohistochemical features of LCH and non-LCH PG in an attempt to determine differences between them that would show that they are two distinct entities. MATERIALS AND METHODS An archival number of 56 cases that were diagnosed as PG and as epulis granulomatosa with complete patient records in the Department of Oral Medicine and Oral Pathology at Dental School of University of Thessaloniki between 2001 and 2003 were retrieved. The slides were reviewed by two of