All of the following ovarian tumours usually occur bilaterally, except:
**Core Concept**
Ovarian tumours can be broadly categorized into epithelial, germ cell, and sex cord-stromal tumours, each with distinct characteristics and clinical presentations. Bilateral ovarian involvement is more commonly associated with certain types of ovarian tumours.
**Why the Correct Answer is Right**
The correct answer is related to the type of ovarian tumour that typically presents unilaterally. Germ cell tumours, such as dysgerminomas, are more likely to occur unilaterally, whereas epithelial tumours and sex cord-stromal tumours often present bilaterally.
**Why Each Wrong Option is Incorrect**
**Option A:** Dysgerminomas are a type of germ cell tumour that typically occur unilaterally, making this option correct for the question, so we skip it.
**Option B:** Serous cystadenocarcinomas are a type of epithelial tumour that often occur bilaterally, so this option is incorrect.
**Option C:** Granulosa cell tumours are a type of sex cord-stromal tumour that can occur bilaterally, making this option incorrect.
**Option D:** Mucinous cystadenocarcinomas are another type of epithelial tumour that often present bilaterally, so this option is also incorrect.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that germ cell tumours, such as dysgerminomas, are more likely to occur unilaterally, whereas epithelial and sex cord-stromal tumours often present bilaterally.
**Correct Answer:** A. Dysgerminomas.