**Core Concept**
Elevated CA 125 levels in epithelial ovarian tumors indicate possible recurrence, metastasis, or persistent disease, necessitating further evaluation to determine the extent of spread and guide management.

**Why the Correct Answer is Right**
The correct answer involves imaging studies to assess for tumor spread and identify potential sites of metastasis. CT scans of the abdomen and pelvis are particularly useful in evaluating the extent of disease, as they can detect enlarged lymph nodes, ascites, and metastatic lesions in the liver, lungs, and other organs. This information is crucial for determining the need for surgery, chemotherapy, or other treatments.

**Why Each Wrong Option is Incorrect**
**Option A:** Ultrasound is useful for evaluating ovarian masses and guiding biopsies, but it is not the primary imaging modality for assessing the extent of disease in recurrent ovarian cancer.

**Option B:** MRI can provide detailed images of pelvic structures and detect small tumors, but it is not the preferred imaging modality for evaluating the extent of disease in recurrent ovarian cancer.

**Option C:** PET-CT is useful for detecting metabolic activity in tumors and can be useful in evaluating the response to treatment, but it is not the primary imaging modality for assessing the extent of disease in recurrent ovarian cancer.

**Clinical Pearl / High-Yield Fact**
In patients with recurrent epithelial ovarian cancer, the CA 125 level can be elevated in the absence of detectable disease, emphasizing the need for imaging studies to assess for tumor spread and guide management.

**Correct Answer:** C. CT scan of the abdomen and pelvis.