Thornwaldt’s cyst is seen in:
**Core Concept**
Thornwaldt's cyst is an uncommon type of nasopharyngeal cyst that arises from the remnant of the notochord, specifically from the remnants of the embryonic hypopharyngeal bursa. The bursa is a temporary structure that is present during embryonic development, and it usually regresses by the fifth week of gestation. However, in some cases, remnants of the bursa can persist and give rise to Thornwaldt's cyst.
**Why the Correct Answer is Right**
Thornwaldt's cyst typically presents as a midline nasopharyngeal mass, often located in the posterior wall of the nasopharynx. It is usually asymptomatic but can cause nasal obstruction, difficulty swallowing, or other symptoms if it becomes large enough to compress surrounding structures. The cyst is lined by a pseudostratified columnar epithelium and is filled with a mucinous or serous fluid. The exact pathogenesis of Thornwaldt's cyst is not well understood, but it is thought to arise from the metaplastic transformation of the epithelial lining of the nasopharynx.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is not relevant to Thornwaldt's cyst, which is a specific type of nasopharyngeal cyst.
**Option B:** While nasopharyngeal carcinoma is a type of cancer that can occur in the nasopharynx, it is not related to Thornwaldt's cyst, which is a benign condition.
**Option C:** A ranula is a type of mucocele that occurs in the floor of the mouth, not in the nasopharynx, so it is not related to Thornwaldt's cyst.
**Clinical Pearl / High-Yield Fact**
It's essential to distinguish Thornwaldt's cyst from other nasopharyngeal masses, such as nasopharyngeal carcinoma or a nasopharyngeal abscess. A thorough history, physical examination, and imaging studies, such as MRI or CT scans, can help diagnose Thornwaldt's cyst.
**Correct Answer: C. A ranula is a type of mucocele that occurs in the floor of the mouth, not in the nasopharynx, so it is not related to Thornwaldt's cyst.