125 E pulides are a common group of oral lesions which account for 40 per cent of all oral neoplasms in dog. There is considerable confusion about the use of the term epulis in veterinary literature. It simply refers to localized gingival enlargment and encom- passes both non-neoplastic reactive and neoplastic lesions (Bostoch, 1987; Dubielzig, 2002). Canine epulides differ strikingly in clinical behav- iour. Fibromatous epulis of periodontal ligament origin, also called peripheral odontogenic fibroma by Gardner and Baker (1991) and ossifying epulides are considered inflammatory and hyper- plasic lesions. On the contrary, acanthomatous ameloblastoma (Gardner, 1993; Head, 2003), pre- viously called acanthomatous epulides because ori- gins from odontogenic epithelial cells found near the tooth or in the gingival epithelium (Dunne, 2001), despite its benign histological appearance, usually shows a malignant biological behaviour (Yoshida, 1999, b). Acanthomatous ameloblastoma is considered an aggressive tumor of the canine jaw, characterized by an irregular verrucous masses adjacent to the tooth, consisting of sheets of no keratinizing odontogenic epithelium, with peripheral palisading epithelium and abundant central acanthocytes with prominent inter- cellular bridges. (Head, 2003). Characteristically, epithelial cells have an infiltrative growth and invade the deep sub mucosa.These lesions are in fact local- ly invasive, with repeated recurrences following sur- gery (Backer, 1993; Gardner, 1993) and can change into malignant tumors when they invade bone and after irradiation (Thrall, 1981; Thrall, 1984). Moreover,recurrent tumors are more aggressive and anaplastic than primary tumour, and have a biologi- cal behaviour similar to that of squamous cell carci- noma (Head, 2003). Several studies, in veterinary medicine, have con- sidered nuclear morphometric analysis as an useful diagnostic predictor in various cancers (mast cell ©2006, European Journal of Histochemistry The aim of this study was to evaluate whether morphometrical analysis can be of diagnostic value for canine acanthomatous ameloblastoma. We calculated, by means of an automated image analyser, some morphometric nuclear parameters, in par- ticular: mean nuclear area (MNA), mean nuclear perimeter (MNP), maximum and minimum diameters (MDx and MDm) coefficient of variation of the nuclear area (NACV), largest to smallest dimension ratio (LS ratio), and form factor (FF), in 8 canine acanthomatous ameloblastomas, and we compared these morphometric data to those of 13 squamous cell carci- nomas of canine gingiva. The results indicated a progressive increase of the MNA, NACV, MNP and MDm proceeding from acanthomatous ameloblastomas (MNA: 42.11±8.74; NACV: 28,36±7,23; MNP: 24.18± 2.68; MDm: 5.69±0.49) to squa- mous cell carcinomas (MNA:49,69±9,10; NACV: 30,89±7,75; MNP: 25.63±2.54; MDm: 6.64±0.73). On the contrary, the LS ratio and the FF resulted greater in acanthomatous ameloblas- tomas (LS ratio: 1,63±0,12; FF: 1,13±0,002) than in SCCs (LS ratio: 1,40±0,12; FF:0.91±0.38). Moreover, the MNA, MNP,MDx and MDm resulted similar (MNA: p=0.89; MNP: p=0,65; MDm: p=0,16; MDx: p=0,13) in a subset of four acanthomatous ameloblastomas with cellular atypia (MNA:49,01±6,88; MNP: 26,28±1,99; MDm: 6.08±0.41; MDx: 10.18±0.88) and in squamous cell carcinomas (MNA:49.69±9,10; MNP: 25.63±2.54; MDm: 6.64±0.73; MDx: 9.26±1.05). While the NACV values resulted higher in typical acanthomatous ameloblastoma (29,99±6,06) than in atypical acanthomatous ameloblastoma (26,74±8,84) and similar to those of the SCCs (30,89±7,75). These results seem to confirm that acanthoma- tous ameloblastoma is a malignant or potentially malignant lesion and emphasizes that nuclear morphometry analysis can be an useful diagnostic and prognostic method in canine oral pathology. Key words: acanthomatous ameloblastoma, dog, nuclear morphometry, squamous cell carcinoma. Correspondence: Manuela Martano, Dipartimento di Patologia e Sanità Animale, Facoltà di Scienze Biotecnologiche, Università degli Studi di Napoli Federico II, Via Delpino 1, 80137 Naples, Italy Tel: +39.81.440301/447176. Fax: +39.81.446746. E-mail: manuela.martano@unina.it Paper accepted on April 4, 2006 European Journal of Histochemistry 2006; vol. 50 issue 2 (Apr-Jun):125-130 Nuclear morphometry in canine acanthomatous ameloblastomas and squamous cell carcinomas M. Martano,* S. Damiano, B. Restucci, O. Paciello, V. Russo, P. Maiolino *Dipartimento di Patologia e Sanità Animale, Settore Anatomia Patologica, Facoltà di Scienze Biotecnologiche, Università degli Studi di Napoli Federico II; Dipartimento di Patologia e Sanità Animale, Settore Anatomia Patologica, Facoltà di Medicina Veterinaria, Università degli Studi di Napoli Federico II, Italy ORIGINAL PAPER 2006_02.qxd 7-07-2008 12:15 Pagina 125