What is the most likely cause of heavy and prolonged vaginal bleeding in a woman with a lesion in the uterine cavity as seen on pelvic ultrasound?

Most Likely Cause: Submucosal Leiomyoma

A discrete lesion within the uterine cavity on ultrasound in a woman presenting with heavy and prolonged menstrual bleeding is most consistent with a submucosal leiomyoma (Answer C), as submucosal fibroids directly impinge on the endometrial surface and disrupt normal hemostatic mechanisms, making them the primary cause of heavy menstrual bleeding when such a lesion is identified. 1

Diagnostic Reasoning

Why Submucosal Leiomyoma is Most Likely

• Submucosal fibroids are specifically associated with heavy and prolonged bleeding patterns, which matches this patient's presentation perfectly 1
• The ultrasound finding of a lesion in the uterine cavity is pathognomonic for either a submucosal leiomyoma or endometrial polyp 1
• Excessive uterine bleeding is usually due to a submucous myoma or an intramural myoma encroaching into the uterine cavity 2
• Hysteroscopic myomectomy is highly effective in controlling menorrhagia related to submucous myoma, confirming this as a well-established cause-effect relationship 2

Why NOT the Other Options

Endometrial Polyp (Option B):

• While polyps can present as lesions in the uterine cavity, they typically cause intermenstrual bleeding more than the heavy, prolonged menstrual bleeding described in this case 1
• Saline infusion sonohysterography has 97% accuracy in distinguishing leiomyomas from polyps when definitive differentiation is needed 1

Adenomyosis (Option A):

• Adenomyosis does not present as a discrete lesion in the uterine cavity on ultrasound 1
• Instead, it shows diffuse myometrial thickening, heterogeneous echotexture, and an ill-defined endomyometrial junction 1
• The normal-sized uterus on examination makes extensive adenomyosis less likely, as adenomyosis typically causes uterine enlargement 1

Dysfunctional Uterine Bleeding (Option D):

• DUB is a diagnosis of exclusion made only after structural pathology has been ruled out 1, 3
• This patient has a documented structural lesion on ultrasound, which automatically excludes DUB as the diagnosis 1
• When an organic cause of abnormal uterine bleeding cannot be found, only then is the diagnosis of dysfunctional uterine bleeding assumed 3

Next Steps in Management

Diagnostic Confirmation

• If initial transvaginal ultrasound shows a focal endometrial abnormality, saline infusion sonohysterography provides 96-100% sensitivity for further characterization before surgical planning 1, 4
• This can definitively distinguish between submucosal leiomyoma and endometrial polyp with 97% accuracy 1, 5

Treatment Approach

• 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 1, 4
• The levonorgestrel-releasing intrauterine device is the first-choice medical treatment when postponing surgery or awaiting menopause, though the risk of expulsion in women with leiomyomas is approximately 20% 6
• Hysteroscopic myomectomy is highly effective in controlling menorrhagia related to submucous myoma and should be considered if medical management fails 2

Clinical Pitfall to Avoid

Do not assume dysfunctional uterine bleeding when imaging has identified a structural lesion—this is a common error that delays appropriate treatment 1, 3