Differential Diagnosis for a Lump Under the Breast During Pregnancy

Single Most Likely Diagnosis

• Breast cyst or fibroadenoma: These are common benign breast lesions that can become more pronounced during pregnancy due to hormonal changes. The lump's location under the breast, near the rib cage, could be consistent with a breast lesion that has grown or become more noticeable.

Other Likely Diagnoses

• Costochondritis: Inflammation of the cartilage that connects the ribs to the breastbone, which can cause lumps or swellings in the area under the breast near the rib cage. Pregnancy can increase the likelihood of this condition due to changes in posture and rib cage expansion.
• Lipoma: A benign tumor composed of fat tissue, which can occur almost anywhere in the body, including under the breast. Lipomas can become more noticeable during pregnancy due to weight gain and changes in body fat distribution.
• Breast engorgement or mastitis: Although these conditions typically present with more diffuse breast symptoms, a localized area of engorgement or infection could be perceived as a lump under the breast.

Do Not Miss Diagnoses

• Breast cancer: Although less common in pregnant women, breast cancer can occur and may present as a lump. It is crucial to not miss this diagnosis due to its significant implications for both the mother and the fetus.
• Lymphoma: A type of cancer that can cause lymph nodes to swell, potentially forming lumps under the breast or in other areas. Early detection is critical for effective treatment.
• Pulmonary or mediastinal masses: Rarely, masses originating from the lung or mediastinum can present as lumps under the breast if they are large enough to push against the chest wall.

Rare Diagnoses

• Neurofibroma: A rare benign tumor of the nerve tissue, which can occur under the breast and cause a lump.
• Hamartoma: A rare, benign breast tumor that can present as a lump.
• Phyllodes tumor: A rare breast tumor that can be benign, borderline, or malignant, presenting as a rapidly growing lump.

Each of these diagnoses requires careful consideration and appropriate diagnostic workup to determine the cause of the lump under the breast during pregnancy.