In a woman with a 4‑year history of postpartum diastasis recti who now has a palpable lump under the right breast that appears when she sits or performs a Valsalva maneuver, how should I evaluate this finding?

Evaluation of a Palpable Lump Under the Right Breast in a Woman with Known Diastasis Recti

Order a targeted breast ultrasound immediately as the first-line imaging study to rule out a breast mass, as this is the mandatory initial evaluation for any palpable breast finding in a woman of childbearing age. 1, 2, 3

Critical Clinical Distinction Required

The key issue here is determining whether this represents:

• A true breast mass (requiring urgent cancer workup)
• An abdominal wall hernia through the diastasis recti defect (benign but may need surgical repair)

The location "under the right breast" and appearance with Valsalva maneuver (sitting, pushing) strongly suggests an abdominal wall hernia rather than breast pathology, but you must definitively exclude breast cancer first. 1

Immediate Diagnostic Algorithm

Step 1: Breast Ultrasound (First-Line Study)

• Perform targeted breast ultrasound of the area where the lump is palpable, as this has nearly 100% sensitivity for detecting breast masses and is the appropriate initial study for women under 40 years. 1, 2, 3
• The American College of Radiology mandates ultrasound as first-line imaging for palpable findings in women under 30-40 years due to dense breast tissue and high diagnostic yield. 1, 2
• Do not perform mammography first in this age group (she was pregnant 4 years ago, likely in her 30s), as ultrasound is superior for dense breast tissue. 2, 3

Step 2: Physical Examination Details to Document

• Palpate the mass while the patient performs Valsalva maneuver (bearing down, coughing) to determine if it enlarges or becomes more prominent—this is pathognomonic for a hernia. 4, 5
• Examine whether the mass is located within breast tissue proper versus the abdominal wall below the inframammary fold. 1
• Check if the mass reduces when the patient lies supine—hernias typically reduce, breast masses do not. 4, 5
• Assess for a palpable fascial defect in the abdominal wall, which would confirm hernia rather than breast pathology. 4, 5

Step 3: Management Based on Ultrasound Results

If Ultrasound Shows a Breast Mass:

• Simple cyst or clearly benign finding (BI-RADS 2): Return to routine clinical follow-up only, no further imaging needed. 2
• Solid mass with benign features (BI-RADS 3): Perform short-interval ultrasound at 6 months, then every 6-12 months for 1-2 years. 2
• Suspicious features (BI-RADS 4-5): Perform ultrasound-guided core needle biopsy immediately—never fine-needle aspiration, as core biopsy provides histology and hormone receptor status. 1, 2

If Ultrasound Shows No Breast Pathology:

• The lump is almost certainly a hernia through the diastasis recti defect, particularly given the Valsalva-induced appearance. 4, 5
• Order abdominal wall ultrasound or CT scan to characterize the diastasis recti defect and confirm hernia, as imaging guides surgical planning. 4
• Refer to general surgery for evaluation of hernia repair if symptomatic or enlarging. 5

Critical Pitfalls to Avoid

• Never assume this is "just" diastasis recti without imaging—any palpable mass in a woman of childbearing age requires imaging evaluation to exclude breast cancer. 1
• Do not delay imaging because the clinical features seem benign—even experienced examiners show only 73% agreement on malignancy, and breast cancer can present with deceptively benign features. 1, 2
• Do not perform biopsy before imaging, as post-biopsy changes will obscure subsequent image interpretation. 1, 2
• Do not order MRI, PET, or molecular breast imaging as initial evaluation—these have no role in the workup of a palpable mass in this age group. 1, 2
• Recognize that diastasis recti itself does not cause discrete lumps—it causes a midline bulge without a fascial defect, so a unilateral lump "under the right breast" suggests either breast pathology or a hernia, not simple diastasis. 4, 5, 6

Why This Approach Prioritizes Morbidity and Mortality

Breast cancer in young women is rare but highly aggressive when present, with worse prognosis than screen-detected cancers, making timely diagnosis critical for survival. 1 The negative predictive value of ultrasound in this setting exceeds 97%, providing strong reassurance when negative. 1 Missing a breast cancer diagnosis would have catastrophic mortality consequences, whereas a brief ultrasound examination carries no risk and definitively excludes malignancy. 1, 2, 3