Surgical Excision of Digital Mucous Cysts

Matthew M. Tomaino, MD, MBA

Dr. Tomaino or an immediate family member has received royalties from DePuy and Tornier; is a member of a speakers’ bureau or has made paid presentations on behalf of DePuy; and serves as a paid consultant to or is an employee of DePuy.

PATIENT SELECTION

Indications

In most cases, digital mucous cysts are asymptomatic. They may appear suddenly or develop over a period of months. Grooving of the nail may precede the clinical manifestation of the cyst itself by up to 6 months. Often, osteoarthritis of the small joints is noted at the site of cyst emergence. Intermittent spontaneous discharge of cyst contents can occur, and in a significant fraction of cases, cysts may disappear spontaneously. Antecedent trauma has been documented in a small minority of cases. As cysts enlarge, pain is an increasingly common symptom (Figure 1). Patients are also likely to express concern about the appearance of larger cysts. In short, indications for surgical excision include increasing size, nail grooving, and a painful distal interphalangeal (DIP) joint arthrosis.

Contraindications

There are situations in which surgical excision may be contraindicated. These include inordinate thinning of the skin, after which a higher risk of wound healing complication may occur. In such situations, it may be better to temporize by aspirating the cyst—not as a definitive intervention but to avoid the potential morbidity of a surgical incision. An infection of a mucous cyst is also a contraindication. It is much more advisable to treat the infection and wait for induration to resolve before surgical intervention.

PREOPERATIVE IMAGING

Plain radiography findings are not diagnostic for digital mucous cysts. In some cases, they will demonstrate a nonspecific soft-tissue density and adjacent bony involvement consistent with osteoarthritic changes. Advanced imaging is not required in most cases, as the diagnosis is most commonly made by history and physical examination. Ultrasonography reveals a rounded or lobulated mass of markedly hypoechoic appearance with smooth, well-defined walls immediately adjacent to the involved synovial compartment. A tapering margin constitutes the “neck” of the cyst. Ultrasonography is faster and better tolerated than MRI, but MRI is less operator dependent. In MRI, homogeneous low-intensity lesions are seen on T1-weighted images, with markedly increased signal intensity and sharp borders on T2-weighted images. Other cyst features include intracystic septa, satellite cysts, cyst pedicles, osteoarthritis of the DIP joint, subungual cysts, and multiple flattened cysts. CT scanning usually demonstrates a well-defined water density mass with normal surrounding soft tissue.¹ Transillumination with a penlight may assist in making the diagnosis and differentiating digital mucous cysts from giant cell tumors of the tendon sheath.

PROCEDURE

Dermatologic and plastic surgeons have practiced cold steel surgical excision of digital mucous cysts for several decades. This procedure ranges from simple excision of the cyst to wide, radical excision with possible graft² or flap reconstruction. Flaps used for reconstruction have historically been rotation flaps,³ but rhomboid flaps⁴ have been used safely and reliably and may be easier to apply
in selected situations. It is key for those caring for these conditions to recognize that these procedures involve opening a direct communication with the DIP joint.

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