IS Case 180: Sebaceous cyst
Imaging Sciences URMC 2008
Publication Date: 2009-05-21
On mammography, sebaceous cysts are round and circumscribed, and can contains calcifications. Sebaceous cysts have variable ultrasound appearance depending on acuity as described in the below discussion.
On ultrasound, sebaceous cysts are round and circumscribed. Those of recent onset are associated with an edematous hair follicle which extends to the skin as a tail. Internal echogenicity is variable depending upon mixture of keratin and fluid as well as duration of blockage. If there is more fluid or if it is more acute, the cyst will more likely be anechoic. Chronic blockage will have more lipid and keratin within the cyst and will more likely be hyperechoic.
In sebaceous cysts which are contained within the skin, there is inflammatory skin thickening, decreased echogenicity and increased blood flow. Inflamed subcutaneous cysts will be thick-walled and hypoechoic, causing the fat surrounding them to be hyperechoic and have increased blood flow.
Differential diagnosis of sebaceous cyst includes breast cancer with skin involvement. Small cancers arising in ectopic terminal ductal lobular units in the subcutaneous tissue can have early skin involvement.
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