Is a 2.5 × 1.8 × 2.4 cm well‑defined hypoechoic lesion in the deep subcutaneous fat just above the muscle at the right lateral edge of a lower‑segment cesarean‑section scar a normal postoperative finding or scar endometriosis?

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Scar Endometriosis: Not a Normal Finding

A 2.5 × 1.8 × 2.4 cm well-defined hypoechoic lesion in the deep subcutaneous fat at the right lateral edge of a cesarean section scar is NOT a normal postoperative finding and represents scar endometriosis until proven otherwise. This requires surgical excision for both definitive diagnosis and treatment.

Why This is Pathologic

  • Normal postoperative healing does not produce well-defined hypoechoic masses in the subcutaneous tissue years after surgery. 1

  • Scar endometriosis develops in 64-96% of cases following cesarean delivery, making it the most common cause of such lesions in LSCS scars. 2

  • The typical presentation includes a gradually growing nodular mass in or adjacent to the cesarean scar, often with cyclical pain (73.3% of cases) or non-cyclical pain (26.6%). 3

  • The incidence of cesarean scar endometriosis is approximately 0.08%, though likely underdiagnosed and increasing with rising cesarean section rates worldwide. 4, 5

Diagnostic Features Supporting Scar Endometriosis

  • Ultrasound characteristics: Solid hypoechoic mass with well-defined borders in the subcutaneous fat or fascia layer, often with neovascularization (color score 3-4 on Doppler). 4

  • Size range: Mean diameter typically 3.9 ± 1.4 cm, with your lesion at 2.5 cm falling within the expected range. 3

  • Location specificity: Deep subcutaneous fat plane just above muscle at the lateral scar edge is a classic location for implanted endometrial tissue. 4, 6

  • Timing: Scar endometriosis develops 12 months to 21 years after cesarean delivery, so any interval from surgery is possible. 4

Critical Differential Diagnosis

While scar endometriosis is most likely, this lesion could mimic:

  • Incisional hernia (though these are typically not solid hypoechoic masses)
  • Hematoma (would have different temporal evolution)
  • Granuloma or abscess (different clinical presentation)
  • Soft tissue tumor including malignancy (rare but must be excluded) 3

The American Gastroenterological Association emphasizes that hypoechogenicity alone is not diagnostic, and tissue sampling is necessary for definitive diagnosis, especially when malignancy cannot be excluded. 1

Recommended Management Algorithm

  1. Assess Doppler vascularity immediately: High color score (3-4) with neovascularization strongly supports endometriosis and indicates active disease. 4

  2. Correlate with clinical symptoms:

    • Cyclical pain with menses (highly specific for endometriosis)
    • Progressive growth of the mass
    • Bluish discoloration of overlying skin during menses 4, 6

  3. Consider fine needle aspiration cytology (FNAC) if diagnosis uncertain: This can confirm endometriosis and rule out malignancy preoperatively, though it is not always necessary. 6

  4. Proceed to wide surgical excision: This is both diagnostic and therapeutic, with complete excision preventing recurrence and eliminating the small risk of malignant transformation. 4, 6, 3

  5. Ensure adequate margins: Excise the mass with surrounding tissue including involved fascia if necessary, as incomplete excision leads to recurrence. 4

Why Surgical Excision is Mandatory

  • Complete resolution of symptoms occurs in 100% of cases with adequate surgical excision. 3

  • Medical management alone is insufficient and does not address the structural pathology. 5

  • There is a theoretical risk of malignant transformation, though rare, making observation inappropriate. 4

  • Biannual follow-up for two years post-excision shows no recurrence when margins are adequate. 3

Common Pitfalls to Avoid

  • Do not dismiss this as "normal postoperative change" – normal healing does not produce solid masses years after surgery. 3

  • Do not delay diagnosis – the average time from symptom onset to diagnosis is often prolonged due to lack of awareness. 2

  • Do not perform simple biopsy without planning for complete excision – incomplete removal leads to recurrence. 4

  • Do not forget to examine the fascia intraoperatively – endometriosis can extend into deeper layers and must be completely excised. 4

References

1
Guideline

Hypoechoic Lesions on Ultrasound: Clinical Significance and Diagnostic Approach

Praxis Medical Insights: Practical Summaries of Clinical Guidelines, 2025

4
Research

Case report: Caesarean scar endometriosis - A rare entity.

International journal of surgery case reports, 2021

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Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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