A 64-year-old man with right mandibular swelling of 6 months' duration. The plain X-ray showed a well-demarcated, osteolytic, multiloculated, expansive lesion located in the horizontal mandibular ramus. The computed tomography showed an expansive lesion with destruction of the bone cortex. With the provisional diagnosis of probable ameloblastoma, the lesion was resected and biopsied. By means of an interpapillary incision, the mandible was exposed, showing a bulging surface destroyed by a fleshy tumour of dense consistency surrounding the branch of the inferior dental nerve. After careful curettage of the bone cavity, the mandible was reconstructed and the mucosa was replaced. There were no postoperative complications.
The material sent to the pathological anatomy consisted of tumour fragments of about 2x1.5 cm, greyish-white when cut and of firm consistency. Several samples were taken, fixed in formaldehyde, embedded in paraffin and processed using routine techniques: 4m thick sections were cut and stained with haematoxylin-eosin. Representative sections were immunohistochemically studied by the avidin-biotin peroxidase method, using primary antibodies anti epithelial membrane antigen EMA, (Dako M613, USA, 10/500), S-100 protein (Dako, L1845, USA, pre-diluted), neurofilaments (Biogenex 6670-0154, USA), NSE neuro-specific enolase, (Biogenex MU055-VC, USA, 10/1000), CD57 (Becton-Dickinson 7660, USA, 10/500), CD34 (Becton-Dickinson 7660, USA, 10/500), smooth muscle a-actin (Dako MO851, USA, 10/200), desmin (Dako M760, USA, 10/500), and vimentin (Shandon 402255, USA, pred. ). The process was performed following the standard protocol, using positive and negative controls.
Fluorescence in situ hybridisation (FISH) was performed on 50m thick paraffin-embedded sections using an LSI BCR/ABL dual colour mixer (VYSIS Inc, Downers Grove, USA) following the manufacturer's recommended procedure and examined with a Nikon fluorescence microscope with a triple band filter, and a hundred nuclei were studied by two of the authors.
Histologically, the tumour fragments consisted of elongated cells of regular shape and size arranged in interlacing bundles and in "onion bulb" structured whorls. The cell density and intercellular stroma were variable, with some areas showing a myxoid appearance. No palisaded cells or atypical cell pleomorphism or atypical mitoses were observed. Residual fibres of the mandibular nerve trunk were identified at the periphery of some fragments. With the provisional diagnosis of PIN, complementary examinations were performed.
Immunohistochemistry showed that the tumour cells were strongly positive for EMA and vimentin and negative for S-100 protein, NSE, collagen IV, CD57, smooth muscle a-actin, desmin and CD34. Schwann cells in the whorls were positive for S-100 protein and axons positive for anti-neurofilament antigen were identified in the centre of the "bulbs". Residual dental nerve fibres were positive for S-100 protein, NSE and neurofilaments and the perineurium positive for EMA.
Fluorescence in situ hybridisation revealed deletion of the long arm of chromosome 22 (22q11) in the nuclei of 75% of tumour cells as well as centromere loss of chromosome 22.
