Most Likely Diagnosis: Submucosal Leiomyoma
The most likely cause of heavy and prolonged vaginal bleeding in this woman with a lesion in the uterine cavity on ultrasound is a submucosal leiomyoma (Option C).
Diagnostic Reasoning
Why Submucosal Leiomyoma is Most Likely
Submucosal fibroids are the primary cause of heavy menstrual bleeding when a discrete lesion is identified within the uterine cavity on ultrasound, as they directly impinge on the endometrial surface and disrupt normal hemostatic mechanisms 1.
The ultrasound finding of a lesion IN the uterine cavity is pathognomonic for either a submucosal leiomyoma or endometrial polyp, and submucosal fibroids are specifically associated with heavy and prolonged bleeding patterns 2, 3.
Excessive uterine bleeding is usually due to a submucous myoma or an intramural myoma encroaching into the uterine cavity, making this the most likely structural cause given the imaging findings 3.
Why Other Options Are Less Likely
Endometrial Polyp (Option B):
- While polyps can present with a lesion in the uterine cavity, saline infusion sonohysterography has 97% accuracy in distinguishing leiomyomas from polyps when needed for definitive differentiation 4, 1.
- Polyps typically cause intermenstrual bleeding more than the heavy, prolonged menstrual bleeding described here 5.
Adenomyosis (Option A):
- Adenomyosis does not present as a discrete lesion in the uterine cavity on ultrasound; instead, it shows diffuse myometrial thickening, heterogeneous echotexture, and an ill-defined endomyometrial junction 5.
- The normal-sized uterus on examination makes extensive adenomyosis less likely, as adenomyosis typically causes uterine enlargement 5.
Dysfunctional Uterine Bleeding (Option D):
- DUB is a diagnosis of exclusion made only after structural pathology has been ruled out 5.
- The presence of a discrete lesion on ultrasound definitively excludes this diagnosis, as DUB represents non-structural causes of bleeding 5.
Clinical Significance and Next Steps
Hysteroscopic myomectomy is highly effective in controlling menorrhagia related to submucous myoma and should be the definitive diagnostic and therapeutic intervention 3, 6.
If initial transvaginal ultrasound shows a focal endometrial abnormality, saline infusion sonohysterography can provide 96-100% sensitivity for further characterization before surgical planning 4, 1.
Medical therapy should be attempted first unless the structural pathology clearly requires surgery, with options including levonorgestrel-releasing IUD, combined oral contraceptives, or tranexamic acid 5, 1.
Key Clinical Pitfall
Do not assume all intrauterine lesions are polyps—submucosal leiomyomas are more commonly associated with the heavy, prolonged bleeding pattern described and require different surgical approaches (hysteroscopic myomectomy vs. polypectomy) 3, 6.