A sebaceous cyst is a term commonly used to refer to either:
Epidermoid cysts (also termed epidermal cysts, infundibular cyst)
Pilar cysts (also termed trichelemmal cysts, isthmus-catagen cysts)Both of the above types of cysts contain keratin, not sebum, and neither originates from sebaceous glands. Epidermoid cysts originate in the epidermis and pilar cysts originate from hair follicles. Technically speaking, then, they are not sebaceous cysts. "True" sebaceous cysts,  which originate from sebaceous glands and which contain sebum, are relatively rare and are known as steatocystoma simplex or, if multiple, as steatocystoma multiplex. Medical professionals have suggested that the term "sebaceous cyst" be avoided since it can be misleading. : 31  In practice, however, the term is still often used for epidermoid and pilar cysts. Signs and symptoms
The scalp, ears, back, face, and upper arm, are common sites of sebaceous cysts, though they may occur anywhere on the body except the palms of the hands and soles of the feet. They are more common in hairier areas, where in cases of long duration they could result in hair loss on the skin surface immediately above the cyst. They are smooth to the touch, vary in size, and are generally round in shape.
This reflects involvement of the anterior interosseous nerve.Sensory changes may be found in the first three fingers as well as in the palm, indicating impairment of the median nerve proximal to the flexor retinaculum, but tend to involve the sensation of the entire hand going numb at night, with any pressure on the median nerve on the areas at the inside of the elbow.The clinical and electrophysiological features of pronator teres syndrome are quite different from patients with carpal tunnel syndrome or pure anterior interosseous syndrome, and are typically normal. Proper localisation is crucial to treatment options.Conduction velocity of the median nerve in the proximal forearm may be slow but the distal latency and sensory nerve action potential at the wrist are normal.Although MRI may show denervation atrophy of the affected muscles, its role in the evaluation of pronator teres syndrome is unclear.⁠
If the EMG or the MRI are abnormal for the pronator teres muscle and the flexor carpi radialis, this implies that the problem is at or proximal to the elbow, as the takeoff of the nerves to these muscles occurs proximal to the elbow. Treatment
Injection of corticosteroids into the pronator teres muscle may produce relief of symptoms.Massage therapy can also provide relief for individuals experiencing this condition.Surgical decompression can provide benefit in selected cases. References


== External links ==