MFDS Oral Pathology — Questions and Answers
Question 1: A radiolucent lesion is found at the apex of a non-vital lower premolar. Histological examination reveals a cyst lined by non-keratinised stratified squamous epithelium with arcading pattern and cholesterol clefts in the wall. What is the most likely diagnosis?
- Dentigerous cyst
- Radicular (periapical) cyst (Correct answer)
- Odontogenic keratocyst
- Lateral periodontal cyst
Correct answer: Radicular (periapical) cyst
A radicular cyst is the most common odontogenic cyst, arising from epithelial cell rests of Malassez stimulated by inflammation from a non-vital tooth. The characteristic histological features include non-keratinised stratified squamous epithelium with an arcading (net-like) pattern, and the cyst wall typically contains chronic inflammatory cells, cholesterol clefts surrounded by multinucleated giant cells, and haemosiderin deposits.
Question 2: Which odontogenic tumour is characterised by the histological appearance of ameloblast-like cells arranged in a follicular or plexiform pattern with stellate reticulum-like areas?
- Odontoma
- Ameloblastoma (Correct answer)
- Cementoblastoma
- Myxoma
Correct answer: Ameloblastoma
Ameloblastoma is a locally aggressive benign odontogenic tumour that recapitulates the enamel organ. The follicular pattern shows islands of epithelium with peripheral tall columnar cells (resembling ameloblasts) showing reverse nuclear polarity, surrounding central areas of loosely arranged cells resembling stellate reticulum. The plexiform pattern shows anastomosing strands and sheets of epithelium. It most commonly occurs in the posterior mandible.
Question 3: What is the most common malignant tumour of the oral cavity?
- Adenoid cystic carcinoma
- Mucoepidermoid carcinoma
- Squamous cell carcinoma (Correct answer)
- Malignant melanoma
Correct answer: Squamous cell carcinoma
Squamous cell carcinoma accounts for approximately 90% of all malignant tumours of the oral cavity. The most common sites are the lateral border of the tongue and the floor of the mouth. Major risk factors include tobacco use, alcohol consumption (synergistic effect), betel quid chewing, and HPV infection (particularly for oropharyngeal SCC). The TNM staging system is used for classification, and treatment typically involves surgery with or without adjuvant radiotherapy.
Question 4: A 12-year-old patient presents with a well-defined radiolucent area surrounding the crown of an unerupted lower second premolar. What is the most likely diagnosis?
- Radicular cyst
- Dentigerous (follicular) cyst (Correct answer)
- Ameloblastoma
- Stafne bone cavity
Correct answer: Dentigerous (follicular) cyst
A dentigerous cyst is the second most common odontogenic cyst, developing from the reduced enamel epithelium and attached to the cemento-enamel junction of an unerupted tooth. It presents as a well-defined unilocular radiolucency surrounding the crown of an unerupted tooth, most commonly lower third molars, upper canines, and lower premolars. Treatment is enucleation with removal of the associated tooth, or marsupialization if the tooth may erupt.
Question 5: What are the histological features that distinguish an odontogenic keratocyst (OKC) from other odontogenic cysts?
- Thick, non-keratinised epithelial lining with rete ridges
- Thin, regular parakeratinised stratified squamous epithelium (5-8 cells thick) with a corrugated surface, prominent basal layer with palisading, and absence of rete ridges (Correct answer)
- Ciliated columnar epithelium resembling respiratory mucosa
- Mucous-secreting epithelium with goblet cells
Correct answer: Thin, regular parakeratinised stratified squamous epithelium (5-8 cells thick) with a corrugated surface, prominent basal layer with palisading, and absence of rete ridges
The OKC (now reclassified as odontogenic keratocyst in the 2017 WHO classification, reverting from 'keratocystic odontogenic tumour') has distinctive histology: a thin, regular parakeratinised stratified squamous epithelium typically 5-8 cells thick with a corrugated (wavy) surface, a well-defined palisaded basal layer of cuboidal or columnar cells, and characteristically lacks rete ridge formation. The lumen contains desquamated keratin. These features, along with its high recurrence rate, distinguish it from other odontogenic cysts.
Question 6: A biopsy of a palatal swelling reveals a tumour composed of a mixture of epithelial and myoepithelial cells in a chondromyxoid stroma. What is the most likely diagnosis?
- Mucoepidermoid carcinoma
- Pleomorphic adenoma (mixed tumour) (Correct answer)
- Warthin tumour
- Acinic cell carcinoma
Correct answer: Pleomorphic adenoma (mixed tumour)
Pleomorphic adenoma is the most common salivary gland tumour, accounting for approximately 60% of all salivary neoplasms. It shows great histological diversity ('pleomorphic') with a mixture of epithelial cells (forming ducts and sheets), myoepithelial cells, and mesenchymal-like stroma (chondroid, myxoid, or fibrous). The palate is the most common intraoral site (minor salivary glands). Despite being benign, it has a tendency to recur if incompletely excised.
MFDS Oral Pathology
A radiolucent lesion is found at the apex of a non-vital lower premolar.
Histological examination reveals a cyst lined by non-keratinised stratified squamous epithelium with arcading pattern and cholesterol clefts in the wall.
What is the most likely diagnosis?