Nipple inversion occurs when the nipple retracts inward instead of protruding outward from the areola. While nipple variations are common, and slight asymmetry in breast structure is normal, the sudden or unilateral appearance of an inverted nipple warrants attention. The change itself, especially when affecting only one side, necessitates a closer look to determine if it is a normal variation or a sign of an underlying process.
The Anatomy of Nipple Inversion
The structure of the nipple is complex, composed of smooth muscle fibers, glandular tissue, and a network of lactiferous ducts. Nipple inversion occurs when the tissue underneath the nipple pulls it inward. The primary physical mechanisms involve short lactiferous ducts or fibrous tissue that tethers the nipple to the underlying breast tissue.
The degree of inversion is often classified by three grades. Grade 1 is mild, where the nipple can be easily pulled out and maintains its projection. Grade 2 is moderate, where the nipple can be pulled out but retracts immediately upon release. Grade 3 is the most severe, with the nipple being permanently retracted due to severe fibrosis and significantly shortened ducts.
Distinguishing Congenital vs. Acquired Inversion
The most significant distinction when evaluating an inverted nipple is whether it has always been present or is a recent change. Congenital inversion, which affects up to 20% of the population, is a benign developmental variation, often affecting both breasts, but it can occur unilaterally.
Acquired inversion develops later in life, involving a previously protruding nipple retracting inward. This change is the primary reason for concern and requires medical investigation, especially when unilateral. A change to a fixed, inverted state should be considered acquired. The most informative question in a medical evaluation is whether the nipple has always been this way or if the change is recent.
Specific Causes of New Unilateral Inversion
A new, unilateral inversion suggests a process is happening within the breast tissue to pull the nipple inward. This retraction is caused by the development of fibrosis, or scar tissue, in the ducts or the tissue beneath the nipple. The causes of this acquired, one-sided inversion are divided into benign inflammatory conditions and suspicious pathologies.
Benign Causes
Benign causes are often related to inflammation or trauma. Mammary duct ectasia is a non-cancerous condition where a milk duct widens, its walls thicken, and it can become blocked, leading to inflammation and subsequent fibrosis that pulls the nipple inward. Infections like mastitis or a subareolar abscess can also lead to scar tissue formation and inversion as the body heals. Other benign causes include fat necrosis (a lump after trauma) and postsurgical changes.
Suspicious Causes
A new, fixed, non-reducible unilateral inversion can be a sign of malignancy and must be investigated. Certain types of breast cancer, such as ductal carcinoma, can infiltrate and shorten the lactiferous ducts, physically tethering the nipple to the tumor underneath. Inflammatory breast cancer or Paget’s disease of the nipple are other malignancies that can present with nipple changes. Suspicion increases if the inversion is accompanied by:
- A new lump
- Bloody or yellowish nipple discharge
- Changes to the skin texture, such as dimpling
Practical Considerations and Medical Consultation
For those with long-standing, congenital inversion, the condition is usually harmless, though it may present challenges with breastfeeding depending on the grade. Many individuals with Grade 1 or 2 inversion can still breastfeed successfully, as the infant latches onto the areola. However, any new, acquired, or changing unilateral inversion must prompt a consultation with a healthcare professional.
The primary goal of medical evaluation is to rule out serious underlying conditions. The doctor will perform a physical examination to check for lumps and assess the reducibility of the inversion. Imaging tests are usually ordered, including a diagnostic mammogram and a breast ultrasound, focusing on the area behind the nipple. For individuals under 30, ultrasound is often the initial imaging study used.