A sebaceous cyst, also known as an epidermoid cyst, is a common skin growth that can occur anywhere on the body. They are generally non-cancerous and can range in size from a few millimeters to several centimeters. Sebaceous cysts form when keratin, a protein found in skin cells, and sebum, an oily substance secreted by sebaceous glands, get trapped under the skin and form a cystic sac. The cyst continues to grow as more keratin and sebum are produced and accumulate inside it.
Typical size of a sebaceous cyst
In most cases, sebaceous cysts remain small, less than 5 cm in diameter. The average size is estimated to be between 2-4 cm. Small sebaceous cysts may go unnoticed for long periods and only come to attention when they become inflamed or infected. Larger cysts are more readily apparent as they form visible or palpable lumps under the skin.
How large can sebaceous cysts grow?
While sebaceous cysts usually remain small, they can continue to slowly expand over time and reach several centimeters in diameter. There are reports of extremely large sebaceous cysts exceeding 10 cm across, although such cases are rare.
Some factors that allow a sebaceous cyst to grow very large include:
- Location on the body where there is abundant space for outward expansion, such as the back, arms, legs, or scalp.
- Minimal or no symptoms causing the cyst to be undetected and untreated.
- Repeated infection and inflammation causing accumulation of fluid and debris.
- High sebum production in the area of the cyst.
- Weakness or absence of the cyst wall allowing unlimited growth.
Case reports of large sebaceous cysts
There are documented medical reports of unusually large sebaceous cysts that highlight their growth potential:
- A 30-year old man developed a sebaceous cyst on his upper back that slowly enlarged over 10 years to reach 15 cm in diameter.
- A 60-year old woman had a large sebaceous cyst on her upper arm that grew to 7 x 10 cm over 5 years.
- A newborn baby was found to have a 5 x 7 cm cyst on the scalp that was present since birth.
- A 6-year old girl developed an extremely large cyst on her upper back that grew to 13 x 21 cm before being surgically removed.
Giant sebaceous cysts
In very rare instances, some sebaceous cysts evolve into giant cysts exceeding 20 cm in diameter. These may develop over many years on the scalp, back, or abdomen of elderly adults. Giant sebaceous cysts pose challenges for surgical removal and skin closure.
Some examples of documented giant sebaceous cysts include:
- A geriatric man with a 30 x 40 cm cyst on his upper back.
- A 72-year old man with a massive 60 cm diameter cyst on his scalp.
- A 75-year old woman with a 35 cm cyst on her upper back.
What causes overgrowth of sebaceous cysts?
The exact reasons why some sebaceous cysts grow to abnormally large sizes are not fully understood. Possible contributing factors include:
- Genetics – Genetic mutations leading to increased sebum production may promote cyst enlargement.
- Hormones – Hormonal changes such as puberty, pregnancy and menopause that increase sebum secretion can play a role.
- Weak cyst wall – A defective cyst wall that ruptures easily can allow unlimited outward growth.
- Infections – Repeated infection and inflammation weakens the cyst wall and increases fluid accumulation.
- Trauma – Injury to the cyst can rupture the wall and trigger rapid enlargement.
- Location – Cysts on the scalp, back and abdomen have room for unchecked growth.
Complications of large sebaceous cysts
While most small sebaceous cysts have minimal symptoms and remain harmless, giant cysts can lead to complications such as:
- Ulceration – The overlying skin becomes thin and ulcerates, causing bleeding and fluid discharge.
- Infection – Bacteria enter through ulcerated skin and cause recurrent infections.
- Pain – Large cysts may press on nerves causing significant pain.
- Restricted mobility – Giant cysts on the back or scalp can restrict neck and limb movements.
- Psychological effects – Social anxiety and low self-esteem due to unsightly appearance.
Diagnosing an oversized sebaceous cyst
Enlarged sebaceous cysts are usually diagnosed based on clinical evaluation of the characteristic features. Additional tests may include:
- Imaging – Ultrasound, CT scan or MRI to determine the size and position of the cyst.
- Biopsy – Microscopic examination of cyst fluid or wall cells.
- Culture – Identifying bacteria responsible for infection of the cyst.
- Blood tests – Checking for conditions like lipid storage disorders associated with cysts.
Treatment for overgrown sebaceous cysts
Management of enlarged sebaceous cysts may involve:
- Incision and drainage – Draining fluid from infected cysts to relieve pain and inflammation.
- Oral antibiotics – Prescribed for treating infection and preventing recurrence.
- Injectable steroids – Reducing inflammation in inoperable giant cysts.
- Surgical excision – Complete cyst removal to prevent reaccumulation of fluid and growth.
- Reconstruction surgery – Repairing skin defects after giant cyst removal.
Preventing overgrowth of sebaceous cysts
Steps that may help prevent sebaceous cysts from becoming abnormally large include:
- Avoid pressing, poking or traumatizing existing cysts.
- Keep the area clean to prevent infection.
- See a doctor for evaluation of new, rapidly growing or painful cysts.
- Consider prophylactic removal of asymptomatic medium-sized cysts.
- Follow up regularly to monitor previously drained cysts.
- Take prescribed antibiotics fully to treat cyst infections.
Conclusion
While most sebaceous cysts remain small and innocuous, some continue to expand to reach very large sizes over 5-10 cm. Extremely rarely, sebaceous cysts may evolve into giant lesions exceeding 20 cm in diameter, requiring complicated surgery. Catching and treating enlarging sebaceous cysts early can prevent disfiguring overgrowth and complications. Creating public awareness and performing regular self-skin examinations are key for the timely detection of problematic cysts needing medical intervention.