Mucous Cyst

In 60-80% of cases, mucous cysts are associated with degenerative joint disease of the DIP joint. Studies have shown a pedicle between the cyst and the DIP joint capsule.[5, 6, 7]

The precise etiology of mucous cysts is unclear; proposed causes have included synovial herniation, extensor retinacular metaplasia, myxomatous degeneration, and excess hyaluronic production by fibroblasts.

Mucous cysts are most common in the fifth through seventh decades of life. They are substantially more common in women, who constitute roughly 70% of the patients.

The recurrence rate with both cyst and osteophyte excision is 3-12%, compared with a 25-50% recurrence rate with cyst excision alone.

Lee et al conducted a retrospective review of the medical records of 37 patients (42 cases) who had mucous cysts combined with Heberden nodes.[8]  Osteophyte excision without cyst excision was performed. In all cases except one, the cyst regressed without recurrence or a skin complication after osteophyte excision; eight patients experienced postoperative pain and loss of range of motion (ROM).

Fan et al studied the results of osteophyte excision and joint debridement in the treatment of mucous cysts of the DIP joint (N = 15; 19 finger sites).[9]  Of the 15 patients, 14 recovered well, and one had partial skin necrosis that healed after dressing changes. In all affected fingers, the postoperative visual analogue scale (VAS) scores were lower than the preoperative scores. In one patient, the ROM of the affected finger decreased; the postoperative activity of the other fingers increased in varying degrees.

On physical examination, the cyst is located between the distal interphalangeal (DIP) extensor crease and the eponychium, lateral to the midline, measuring up to 15 mm (average, 7 mm). The overlying skin can be thick or thin, and the patient may report sporadic drainage of the viscous fluid. Some erythema may surround the ganglion.

Eventually, the cyst may result in a grooved deformity of the nailbed, or a nail groove may be present before the cyst is visible. Patients typically present to their physicians because of the deformity, though some may complain of discomfort.[10, 11, 12, 5, 7, 13]

Differential diagnoses include Heberden nodes or rheumatoid nodules, epidermoid inclusion cyst, Dupuytren knuckle pad, xanthoma, giant cell tumor of the tendon sheath, and gout.

Radiographs may show changes typical of degenerative arthritis, such as joint-space narrowing, subchondral sclerosis, and dorsal osteophytes (see the images below).

Additional studies rarely are needed. The diagnosis usually is made clinically, though magnetic resonance imaging (MRI) can help in difficult cases.

Dermatoscopy may be a useful noninvasive adjuvant in the diagnosis of mucous cysts of the fingers.[14]

Grossly, mucous cysts are cystic, smooth, translucent masses with viscous fluid.

Under light and scanning electron microscopy, mucous cysts share the same ultrastructure as other soft-tissue ganglions. Under light microscopy, ganglions have a smooth collagenous lining. On scanning electron microscopy, crisscrossing layers of collagen are identified, with areas of elevations hypothesized to be multifunctional mesenchymal cells. No major degenerative or inflammatory changes are seen, nor are bursal or synovial endothelial cells. Multiple cavities may be found coalescing into a larger space.

Treatment options for mucous cysts in the past have included aspiration, electrocautery, chemical cautery, steroid injection, and various types of surgical excision. Most of these procedures are associated with significant recurrence rates, though these tend to be lower than those associated with carpal ganglions.

Surgical excision, currently regarded as the definitive treatment, is indicated in the presence of active infection, drainage, or pain. Patients also may complain of nailbed deformity or extensor lag.

There are few contraindications for surgery. Even if the patient has medical comorbidities with concomitant risks with anesthesia, surgery can be performed with a digital block.

Although surgery is considered the definitive treatment for mucous cysts, nonoperative treatments have been employed, including aspiration, electrocautery, chemical cautery, and steroid injection.[15]

Aspiration of digital ganglions was found to have a 65-69% success rate, compared with 27-45% for carpal ganglions. One caveat with aspiration is the risk of infection. In fact, infections of the cyst and subsequently the joint can occur from spontaneous breakdown of the cyst or from iatrogenic aspiration. Such infections must be promptly treated; they often lead to septic arthritis and osteomyelitis with disastrous complications.

Some early authors proposed that low-voltage radiation therapy is associated with a lower recurrence rate than surgical treatment is.[16, 17, 18, 19, 20, 21, 22]

Surgical treatment is recommended in the presence of ongoing pain, recurrent infection, or chronic drainage. Preoperative planning is limited, in that much of the procedure is based on intraoperative findings. In the presence of significant arthritic pain, patient consent can be obtained for a distal interphalangeal (DIP) joint arthrodesis. This can be done with single-screw fixation (eg, an Acutrak or Herbert screw) or with Kirschner wires (K-wires) and cables, depending on the surgeon's preference.

The relevant factors to remember preoperatively are to remove the osteophyte and to obtain adequate skin coverage after excision. Patient consent should be obtained for skin graft or flap coverage[23] if needed.

Depending on the surgeon's preference and the location of the cyst, various surgical incisions can be used, including an H, T, U, or transverse curving incision. (See the image below.)

After the skin is incised, the dissection is continued around the cyst, tracing the stalk down to the joint. Care must be taken to avoid damaging the terminal extensor tendon, the germinal matrix, and the terminal portions of the neurovascular bundles. Depending on the intraoperative findings, a synovectomy, osteophyte resection, and debridement may be performed. A disrupted terminal extensor tendon (whether iatrogenic or cyst-related) should be repaired to prevent subsequent extensor lag.[17, 19, 24, 25, 26, 27, 28]

Studies have shown the necessity of excising not only the cyst but also the underlying DIP osteophyte. Care must be taken to avoid injury to the germinal matrix and to prevent further nail deformity. One study described treatment of fingernail deformities secondary to mucous cysts with removal of the osteophyte only, without excision of the ganglion or skin. In this study of 20 ganglion cysts, the ganglion did not recur in any patients, and two nails had residual grooves.

In the event of significant DIP joint arthritis and pain, an arthrodesis can be performed during the same operation. Chen advocated radical excision of the attenuating skin overlying the cyst, which can contain satellite ducts and lakes of mucoid degeneration.[24]

The surgeon can obtain the patient's consent preoperatively for a skin graft if skin excision leaves extensor tendon or joint exposed. Rotation flaps have been utilized to compensate for excised or thinned skin overlying the cyst. Jager et al reported on their use of the Zimany bilobed flap, utilizing the geometric design developed by Zitelli, in the surgical treatment of nine digital mucous cysts.[29] They recommended this procedure because it is easy and safe, wound healing is fast, and outcomes are good. Jiménez et al reported similarly good results.[30]  Ma et al described good results with a bipedicled advancement flap.[31]

The decision to use skin grafting, a rotational flap, or primary closure is largely surgeon-dependent.[32, 33] In the authors' experience, most incisions can be closed primarily without the need for further coverage procedures.[34, 35, 36]

Percutaneous capsulotomy has been described as a potential minimally invasive alternative for the treatment of digital mucous cysts. In a study by Hsiung et al, with a mean follow-up of 28.8 months (range, 24-33), the recurrence rate was low after this procedure, and patient satisfaction was good.[37]  However, the clinical utility of this approach remains to be established.

Unless an extensor tendon repair or some other procedure requiring joint immobilization is involved, only a light dressing is needed postoperatively. Gentle active range of motion is allowed, and sutures usually are removed after 2 weeks.

Infection is a common complication of mucous cysts, either preoperatively or postoperatively. For that reason, prophylactic antibiotics are used intraoperatively and for 3 days postoperatively.[38, 2]

Complications of surgical treatment include the following:

• Extensor tendon disruption
• Recurrence
• Nail deformity from injury to the germinal matrix

Other potential risks include the following:

• Persistent pain
• Swelling
• Stiffness
• Infection

If a patient continues to experience pain secondary to degenerative joint disease, a DIP joint arthrodesis may be performed later.