Differential Diagnosis for the Right Shoulder Lesion
Single Most Likely Diagnosis
- Epidermoid Cyst: A small, cyst-like area with a small opening and no signs of infection (redness, fluctuance) is consistent with an epidermoid cyst. Gentle pressure not relieving the lesion and the absence of material expression also support this diagnosis.
Other Likely Diagnoses
- Pilar Cyst: Similar to epidermoid cysts, pilar cysts are benign, fluid-filled lesions that can present as small, firm nodules. They are often found on the scalp but can occur on other parts of the body, including the shoulder.
- Dermoid Cyst: Although less common, dermoid cysts can present similarly to epidermoid cysts but may contain hair, teeth, or other tissue. The lack of fluctuance and the small size make this less likely but still a consideration.
- Sebaceous Cyst: These are benign cysts filled with a cheesy material and can have a small opening to the skin. However, they often become inflamed or infected, which is not indicated in this case.
Do Not Miss Diagnoses
- Malignant Tumor (e.g., Basal Cell Carcinoma, Squamous Cell Carcinoma): Although rare, any new or changing skin lesion should be evaluated for the possibility of malignancy. The absence of typical signs of cancer (e.g., rapid growth, ulceration, bleeding) makes this less likely, but it cannot be ruled out without further investigation.
- Infected Cyst or Abscess: Despite the lack of redness or fluctuance, an infected cyst or abscess could present atypically, especially in immunocompromised patients. The small opening could be a sinus tract.
Rare Diagnoses
- Keratoacanthoma: A low-grade, or sometimes considered benign, tumor of the skin that can resemble a cyst but often has a more rapid growth phase and can resolve on its own.
- Trichoepithelioma: A rare, benign tumor of hair follicle origin that can present as a small, firm nodule but is less likely to have a visible opening.
- Pilomatrixoma: A rare, benign skin tumor arising from the hair follicle matrix that can present as a firm, sometimes cystic, nodule but is more common in children and on the face or neck.