Which imaging finding on MRI best discriminates a submucosal fibroid from a submucous polyp in a 42-year-old woman with abnormal uterine bleeding?

Explanation

## MRI Differentiation: Submucosal Fibroid vs Endometrial Polyp ### Pathological Basis **Key Point:** Fibroids are benign smooth muscle tumours with characteristic low T2 signal due to dense smooth muscle bundles, while endometrial polyps are benign mucosal proliferations with high T2 signal (similar to endometrium) and typically a thin stalk. ### MRI Characteristics Comparison | Feature | Submucosal Fibroid | Endometrial Polyp | |---------|-------------------|-------------------| | **T2 signal** | Low (hypointense) | High (hyperintense) | | **Appearance** | Whorled/spiral pattern | Homogeneous | | **Base** | Broad, sessile | Thin stalk (pedunculated) | | **Degeneration** | Common (cystic, hyaline) | Rare | | **Enhancement** | Heterogeneous, delayed | Homogeneous, early | | **Junctional zone** | Distorted | Normal | | **Size** | Often >2 cm | Usually <2 cm | ### High-Yield MRI Pattern **High-Yield:** The **"whorled" or "onion-skin" pattern on T2-weighted imaging** is pathognomonic for fibroids and results from concentric layers of smooth muscle bundles. This is the single most reliable MRI discriminator. Polyps lack this pattern entirely. ### Clinical Pearl **Clinical Pearl:** Submucosal fibroids often show **broad sessile bases** and distort the endometrial cavity, whereas polyps are typically **pedunculated with thin stalks**. On contrast-enhanced imaging, fibroids enhance heterogeneously and slowly (due to fibrous tissue), while polyps enhance homogeneously and early (due to endometrial vascularity). ### Mnemonic **Mnemonic:** **FIBROID** = **F**ibroid = **Low T2** (dense muscle); **P**olyp = **High T2** (endometrial tissue) [cite:Jeffcoate's Principles of Gynaecology Ch 15; DeCherney Obstetrics & Gynaecology 14e Ch 19]