Pilar Cyst Appearance
Pilar cysts are firm, flesh-colored nodules on the scalp, that are easily palpable. The surface is smooth and dome-shaped. Pilar cysts may be difficult to distinguish from epidermal cysts clinically, except by location. Both present as a firm, subcutaneous nodules ranging from 0.5 to 5.0 cm. No central punctum is seen over a pilar cyst, as is found over an epidermal cyst. When dissected, a pilar cyst possesses a tough, white-gray wall that is more resistant to tearing than the wall of an epidermal cyst. The pilar cyst wall separates easily and cleanly from the surrounding dermis. If a pilar cyst ruptures, the area becomes inflamed, red, and tender and boggy on palpation.
Pilar cysts almost always develop after puberty. The tendency to develop pilar cysts often has an autosomal dominant inheritance. Pilar cysts are multiple in 70% of patients who have them. Pilar cysts persist indefinitely and slowly grow to a stable size unless they rupture. Pilar cysts rupture less frequently than epidermal cysts, presumably because the pilar cyst possesses a thicker wall. Rupture usually results from an external trauma. A brisk foreign body inflammatory reaction follows and can be quite painful and resembles a furuncle.
Large cysts may be cosmetically objectionable. Some cysts are so large and tender, they may interfere with wearing hats and helmets. Acute inflammation after rupture is often misdiagnosed as infection. Antibiotics are of little value in such cases. Incision and drainage under local anesthesia improve comfort and limit scarring. Elective excision before rupture prevents this complication.