Pathology of the Head and Neck

242 L. Michaels8.2.5 Malignant Neoplasms8Fig. 8.6. Exostosis of the deep external canal. Note thin epidermallayer on the exostosis and canal skin and their proximity tothe bone. Reproduced from Michaels and Hellquist [68]periosteum merge to form a thin layer. The distancebetween the epidermal surface and underlying bone isconsequently small. This explains the propensity towardsexostoses of the tympanic bone to develop inthis region in those who swim frequently in cold water.It seems likely that the water, after dribbling intothe deep external auditory canal, exerts a cooling effecton the bone surface and stimulates it to producenew bone. Unlike osteoma (Fig. 8.5) the bone formationsof exostosis are said not to possess any marrowspaces (Fig. 8.6).Osteoma and exostosis are often associated with infectionof the external canal on their tympanic membraneside and surgical removal may be required to enhancedrainage as well as to relieve the conductive hearingloss.Five cases of a benign circumscribed bony lesion ofthe external auditory canal distinct from exostosis andosteoma have recently been described [91]. They allshowed a hard, round, unilateral, skin-covered mass occludingthe superficial external auditory canal with norelationship to the cartilaginous tissue or to the bonystructure surrounding that canal. Histologically, thelesion displayed an osteoma-like bone formation withsparse osteoblastic areas; mature lamellar bone was observedsome cases, and also bone marrow containingadipose tissue and hematopoietic remnants. The boneshowed irregular trabeculae, bordered by osteoid osteoblasts.8.2.5.1 Adenocarcinomaof Ceruminal GlandsICD-O:8420/3Adenocarcinoma of ceruminal glands is a rare neoplasmpresenting in the superficial part of the external ear canal.There is always local infiltration. The neoplasmpossesses a glandular structure with evidence of apocrinedifferentiation, but the glands show loss of a myoepitheliallayer and the cells are markedly atypical withincreased mitotic activity. Recurrence is to be expectedfollowing surgical removal. Death due to involvement oflocal vital structures has been reported. Rare examplesof low-grade adenocarcinoma of ceruminal glands havebeen documented.8.2.5.2 Adenoid Cystic Carcinomaof Ceruminal GlandsICD-O:8200/3This malignant neoplasm has the gross and microscopicfeatures of the corresponding major or minor salivarygland neoplasm, including its tendency to invade alongnerve sheaths. Relentless though often delayed recurrenceand eventual bloodstream metastasis, particularlyto the lungs, are likewise features of this cancer.8.2.5.3 Basal Cell CarcinomaICD-O:8090/3The great majority of malignant epithelial neoplasmsof the pinna are basal cell carcinomas, a small numberonly being squamous cell carcinomas. The few basal cellcarcinomas that occur in the ear canal arise near the externalopening. Their preference for the exposed part ofthe external ear is in keeping with the accepted view thatsunlight is in most cases the causal factor in skin insufficientlyprotected by melanin pigment.The gross appearance of basal cell carcinoma is usuallyone of a pearly wax-like nodule that eventually ulcerates.Twenty-five per cent of basal cell carcinomas ofthe pinna are of the morphea type (see below). The importanceof this variety is that although the edge of thetumour tends to infiltrate subcutaneously, this cannotbe recognised clinically or on gross pathological examination.The classical and most frequent form of basalcell carcinoma is composed of solid masses of cells,which are seen to be arising from the basal layers of theepidermis or the outer layers of the hair follicles. Thecells are uniform with basophilic nuclei and little cy-