Mucoid Cysts
What is a
mucoid cyst ?
A mucoid cyst is a benign swelling filled with gelatinous fluid, located at the base of the fingernail, overlying the distal interphalangeal joint.
It is almost always associated with underlying osteoarthritis of this joint: osteophytes (small bony spurs caused by arthritis) create a communication between the joint and the cyst that forms beneath the skin.
A mucoid cyst can cause progressive nail deformity by pressing on the nail matrix, local pain and thinning of the overlying skin. If the skin ruptures spontaneously, there is a real risk of infection spreading to the underlying joint, requiring urgent treatment.
When is surgery needed ?
Unlike synovial cysts of the wrist, mucoid cysts should not be treated by simple aspiration alone : the infection risk and recurrence rate without addressing the underlying arthritis are too high.
Surgery is recommended in the following situations:
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persistent pain or functional limitation
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significant nail deformity
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very thin overlying skin at risk of rupture and infection
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cyst showing signs of fistulation
How is the procedure performed ?
The procedure is performed under regional anaesthesia on a day-case basis (the patient goes home the same day).
It usually combines three steps :
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excision of the cyst with its stalk traced back to the joint
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removal of the osteophytes responsible for the underlying arthritis, to treat the cause and reduce the risk of recurrence
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a local skin flap when the skin overlying the cyst is too thin or necrotic to be closed directly, ensuring quality wound healing
What is the recovery ?
A splint immobilising the tip of the finger is worn for a variable period depending on skin tension, for up to 15 days.
Wound care is carried out for several weeks, particularly when a local flap has been used. The other fingers remain free and mobile throughout.
Physiotherapy may be prescribed to restore full finger mobility. When the underlying arthritis has been adequately treated, the risk of cyst recurrence is low.
What are the risks ?
Risks include:
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partial necrosis of the skin flap, requiring prolonged wound care
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wound or joint infection
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residual stiffness of the distal joint
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persistent nail deformity if the nail matrix was damaged by the cyst prior to surgery
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cyst recurrence in the presence of progressive arthritis