What are the differential diagnoses for a 37‑year‑old woman with difficulty losing weight despite regular exercise, a tubal ligation performed two years ago, and a slightly enlarged uterus on examination?

Differential Diagnoses for Enlarged Uterus in a 37-Year-Old Woman with Weight Loss Difficulty and Prior Tubal Ligation

The most likely diagnosis is uterine leiomyomata (fibroids), which are extremely common in this age group and can cause both uterine enlargement and difficulty losing weight due to the mass effect and metabolic changes. 1

Primary Differential Diagnoses

Uterine Leiomyomata (Fibroids) – Most Likely

• Leiomyomata are detected most commonly on pelvic examination as an enlarged, irregular uterus, and ultrasound is the standard confirmatory imaging modality 1
• The vast majority of leiomyomata remain undiagnosed clinically, with histologic or sonographic evidence present in far more women than those who are symptomatic 1
• Fibroids can contribute to weight retention through direct mass effect (the uterus itself weighs more) and may be associated with metabolic changes 2
• Uterine weight >500g is associated with increased morbidity if surgical intervention becomes necessary 2
• Fibroids may be asymptomatic or cause menorrhagia, pelvic pressure, or bulk symptoms 1

Adenomyosis

• Adenomyosis causes diffuse uterine enlargement and is common in women in their 30s-40s 2
• Typically presents with dysmenorrhea, menorrhagia, and a uniformly enlarged, boggy uterus on examination
• Ultrasound may show heterogeneous myometrial echotexture, though MRI provides superior soft-tissue characterization 1
• Often coexists with leiomyomata 2

Post-Tubal Ligation Complications

• Proximal tubal distension with blood can occur after tubal ligation, causing pelvic pain and potentially contributing to uterine size perception 3, 4
• "Post-ablation-tubal sterilization syndrome" describes swollen, blood-filled proximal tubal segments that can mimic early ectopic pregnancy appearance 4
• This patient had tubal ligation 2 years ago, placing her in the timeframe for developing retrograde menstruation into occluded proximal tubes 3
• Laparoscopy during menstruation may reveal dilated proximal tubal stumps if this is contributing to symptoms 3

Pregnancy-Related Conditions (Must Be Excluded)

• Early intrauterine pregnancy must be ruled out with quantitative β-hCG, even with prior tubal ligation, as sterilization failure occurs in approximately 1 in 200 cases 5, 6
• Ectopic pregnancy remains possible after tubal ligation, particularly interstitial pregnancy, which carries higher rupture risk 5, 7
• Obtain β-hCG, CBC, blood type/Rh, and transvaginal ultrasound if any possibility of pregnancy exists 7, 6
• 84-93% of ectopic pregnancies occur in the fallopian tube, but interstitial, cervical, and cesarean scar locations are possible 5, 7

Endometrial Pathology

• Endometrial hyperplasia or polyps can cause uterine enlargement, though typically less pronounced than fibroids
• Endometrial carcinoma is less likely at age 37 but should be considered if abnormal bleeding is present
• Transvaginal ultrasound will assess endometrial thickness; endometrial thickness ≥25mm virtually excludes ectopic pregnancy but may suggest intrauterine pathology 5

Polycystic Ovary Syndrome (PCOS)

• PCOS is associated with obesity and difficulty losing weight despite exercise, particularly visceral adiposity 8
• PCOS increases insulin resistance and compensatory hyperinsulinemia, which amplifies adipogenesis and decreases lipolysis 8
• PCOS does not typically cause significant uterine enlargement but may contribute to the weight loss difficulty
• Consider if patient has oligomenorrhea, hirsutism, or acne 8

Critical Next Steps Before Sonogram

Immediate Laboratory Evaluation

• Quantitative serum β-hCG is mandatory to exclude pregnancy, even with prior tubal ligation 7, 6
• Complete blood count to assess for anemia from potential menorrhagia 7, 6
• Consider thyroid function tests if weight gain is disproportionate to caloric intake

Clinical History to Elicit

• Menstrual pattern changes: menorrhagia, dysmenorrhea, intermenstrual bleeding 1, 3
• Pelvic pain characteristics: cyclic cramping may suggest retrograde menstruation into tubal stumps 3, 4
• Bulk symptoms: pelvic pressure, urinary frequency, constipation (suggest large fibroids) 1
• Infertility concerns: although tubes are ligated, submucosal fibroids can affect fertility if reversal is considered 1

Physical Examination Findings to Document

• Uterine size, contour, and mobility: irregular contour suggests fibroids; uniformly enlarged suggests adenomyosis 1
• Adnexal masses or tenderness: may indicate ovarian pathology or tubal distension 7
• Cervical motion tenderness: would suggest infection or ectopic pregnancy 1

Sonographic Evaluation Strategy (Scheduled in 3 Weeks)

Transvaginal Ultrasound Should Assess

• Uterine size and myometrial echotexture: fibroids appear as well-defined hypoechoic masses; adenomyosis shows heterogeneous myometrium 1
• Endometrial stripe thickness and regularity: normal is <8mm in non-pregnant state 5
• Adnexal structures: evaluate for ovarian masses, hydrosalpinx, or tubal pathology 1, 7
• Free fluid in pelvis: would suggest rupture, infection, or malignancy 1, 5
• Proximity of any fibroids to endometrial cavity: submucosal location has different management implications 1

If Ultrasound Is Indeterminate

• MRI pelvis provides superior soft-tissue contrast and is the preferred problem-solving modality 1
• MRI is particularly helpful for evaluating fibroid complications including hemorrhage, torsion, or infarction 1
• CT should be reserved for acute presentations due to radiation exposure in reproductive-age women 1

Common Pitfalls to Avoid

• Do not assume tubal ligation provides 100% contraception; pregnancy must be excluded with β-hCG 5, 6
• Do not attribute all weight difficulty to behavioral factors alone; PCOS, hypothyroidism, and large fibroids can contribute 8, 2
• Do not dismiss cyclic pelvic pain in a woman with prior tubal ligation; retrograde menstruation into proximal tubal stumps is a recognized complication 3, 4
• Do not delay ultrasound if patient develops acute pain or bleeding; ectopic pregnancy can occur at any β-hCG level 5, 7
• Do not overlook the possibility of endometriosis, though it is less common after tubal ligation due to prevented retrograde flow 9