The lesion at the apex of a tooth was biopsied and reported as PSEUDOSTRATIFIED CILIATED COLUMNAR epithelium with inflammatory cells. This tissue is most likely part of which structure?

Correct answer: A. The maxillary sinus lining

• A. CORRECT. PSEUDOSTRATIFIED CILIATED COLUMNAR epithelium — respiratory epithelium, or SCHNEIDERIAN MEMBRANE — is the lining of the MAXILLARY SINUS. When a periapical lesion of a maxillary posterior tooth is enucleated, the sinus floor is frequently only a thin plate of bone away, and the specimen can inadvertently include sinus lining. Chronic inflammation in the specimen is consistent with a reactive sinusitis of odontogenic origin, which is the most common cause of unilateral maxillary sinusitis.
• B. A dentigerous cyst is likewise lined by thin non-keratinised stratified squamous epithelium of reduced enamel epithelium origin, and is attached at the CEJ of an unerupted tooth.
• C. The nasal cavity is also lined by respiratory epithelium, but a periapical specimen from a maxillary posterior tooth is anatomically far more likely to have entered the SINUS than the nasal floor.
• D. A radicular cyst is lined by NON-KERATINISED STRATIFIED SQUAMOUS epithelium derived from the rests of Malassez, typically with a hyperplastic arcading pattern, cholesterol clefts and a dense inflammatory infiltrate. Respiratory epithelium is occasionally found in radicular cysts of the posterior maxilla — but only through metaplasia or sinus contamination.

Note: The epithelial lining is often the whole answer in cyst questions. Keratinised with a corrugated parakeratotic surface and a palisaded basal layer = OKC. Ghost cells = calcifying odontogenic cyst. Respiratory epithelium = sinus or nasopalatine duct cyst (the latter may also contain nerves and vessels from the neurovascular bundle).