Head and Neck Pathology

Abstract

Most malignant tumors in the head and neck are conventional keratinizing squamous cell carcinomas, and their microscopic diagnosis usually pose little challenge for pathologists. However, other conditions including rare malignancies can be encountered so infrequently that diagnosis or grading may be challenging. This issue of Pathology Case Reviews attempts to answer some of the more common questions that pathologists ask of their colleagues with an expertise in oral and/or head and neck pathology. These include the diagnosis and grading of oral epithelial dysplasia, the differential diagnosis of basaloid squamous carcinoma, and the relevance of HPV infection in squamous cancer of the oropharynx. Complementary articles discuss the diagnosis and grading of mucoepidermoid carcinoma, the clinical and pathologic features of salivary duct carcinoma, the diagnostic criteria of parathyroid carcinoma, and the microscopic and immunophenotypic features of marginal zone (MALT) lymphoma of the parotid gland. The diagnosis and terminology of precursor lesions to carcinomas of the upper aerodigestive tract is a challenging area for many pathologists because of the subtle microscopic features that form the basis of grading. This area is important because grading often guides clinical management for patients with premalignant disease. In their article, Drs Speight and Torres-Rendon present a case of squamous dysplasia of the oral tongue that progressed to squamous cell carcinoma. They clarify the clinical presentation of oral epithelial dysplasia and provide terminology and the histologic criteria for grading. The practical differential diagnosis and clinical management of oral epithelial dysplasia is also covered. Mucoepidermoid carcinoma is the most common primary malignancy of the salivary glands. Microscopic grading seems to play an important role in treatment selection and patient prognosis, and yet no common grading system has been agreed on. Drs Griffith and Seethala present a case of mucoepidermoid carcinoma arising in a minor salivary gland of the buccal mucosa. They present the differential diagnosis for mucoepidermoid carcinoma and then compare competing microscopic grading systems, problems in their application, and the clinical significance of grading. Salivary duct carcinoma is a rare, high-grade adenocarcinoma of the major salivary glands with a poor prognosis. Despite the distinctive cytologic and histologic features of this tumor and its resemblance to apocrine-type ductal carcinoma of the breast, salivary duct carcinoma can be mistaken for several other high-grade malignancies including mucoepidermoid carcinoma. We present a case of salivary duct carcinoma of the parotid gland and discuss the diagnostic features in fine needle aspirate and histologic samples, including the important role immunohistochemical assessment plays in establishing the diagnosis. Given the prevalence of primary hyperparathyroidism and the routine nature of parathyroid specimens in surgical pathology, a clear understanding of the diagnostic criteria for parathyroid carcinoma is required. Drs Khanafshar and van Zante discuss a case of parathyroid carcinoma, present the diagnostic criteria for a diagnosis of carcinoma and the diagnostic category of atypical adenoma. The applicability of a limited panel of immunostains is additionally reviewed. Another challenging area of head and neck pathology is the diagnosis of marginal zone (MALT) lymphoma, especially given the overlapping findings between long-standing autoimmune sialadenitis and MALT lymphoma. Drs McAlhany, Etzell, and Treseler present a case of MALT lymphoma of the parotid and discuss the histologic features, immunophenotype, and differential diagnosis. Recent advances in the understanding of the etiology of squamous cell cancer of the head and neck has shown that this group of tumors is made up of distinct subtypes with unique biological and histologic features. It has now been established that most squamous cell carcinomas arising in the oropharynx (base of tongue and lingual tonsils) are etiologically associated with oncogenic strains of human papillomavirus (HPV) rather than tobacco and alcohol, the traditional risk factors for head and neck cancer. Many HPV-associated squamous cell carcinomas are nonkeratinizing with a basaloid appearance. In their article, Drs Mills, Stelow, and Mills discuss the diagnosis of basaloid squamous cell carcinoma and highlight the broad differential that must be considered when a basaloid or small cell malignancy is encountered in the head and neck region. Finally, given that treatment paradigms may soon rely on pathologists to differentiate HPV-driven tumors and HPV-negative tumors, pathologists should make an effort now to understand the typical clinical presentation and histology of HPV-associated squamous cell carcinoma. A basic understanding of the indications for and limitations of immunohistochemistry for p16 and in situ hybridization for the identification of high-risk HPV is also required. The final article in this journal is an orientation to HPV-associated squamous cell carcinoma of the oropharynx and provides practical advice on how to evaluate and report squamous cancers of the oropharynx and the clinical implications of the diagnosis.FIGUREFIGURE