On the differential diagnosis of clear cell tumours of the head and neck.

Clear cell tumours, both benign and malignant, derive from a diverse group of epithelial cell types including renal epithelium, keratinising epithelium, cutaneous adnexa, salivary glands, odontogenic epithelium, melanocytes and even mesenchymally derived cells of adipose and tendon sheath. In the head and neck, clear cell tumours represent a singular challenge to the pathologist since the classic morphological features of malignant neoplasia exemplified by cytological atypia are frequently absent in malignant clear cell variants, thereby excluding reliance on this histopathological hallmark for the establishment of a diagnosis. The differential diagnosis of both benign and malignant clear cell tumours must take into account patterns of growth as well as the phenotype of accompanying cell populations when attempting to arrive at a definitive histological diagnosis. In this review article, the histopathology of head and neck tumours that harbour significant clear cell populations will be compared and contrasted.