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1 CHAPTER 46 DIGITAL MUCOID CYSTSR obert M. Goecker DPMM ucous cysts are small cystic lesions that occur intra-dermally on the dorsal aspect of the interphalangeal jointand distal phalanx of the digits. These lesions closelyresemble ganglion cysts histologically. Synonyms for digitalmucoid cysts include cutaneous synovial (mlxoid) cyst,focal cutaneous mucinosis, digital synovial cyst and dorsaldigital ganglion cyst. These cysts are commonly seen by thefoot and ankle surgeon. A review of these lesions includingsurgical treatment options is REVIE\T/Digital mucoid cysts were first described by Hyde andMontgomery in 1883.''' Synonyms for digital mucoidcysts include cutaneous synovial (mlxoid) cyst, focalcutaneous mucinosis, digital synovial cyst and dorsaldigital ganglion cyst.' All of these common descriptivenames can be summarized as dermal "teno-arthro-synovial hernias."t Cysts have similar histology andcharacteristics with loosely formed degenerative connec-tive tissue and a viscous jelly like All cystsreveal mlxoid degeneration histologically but differ intheir body location.

2 Ganglion cysts occur below the skinin the subcutaneous layer versus mucoid cysts which arepresent within the dermal Digital mucoid cysts aresoft, smooth, raised, oval to round, translucent, white topink, solitary, slow-growing structures that are usuallyseen distally on toes and fingers. These lesions have aFigure 1A. A classic digital mucoid c\rst over the second distal clinical appearance although other conditions suchas pyogenic granuloma, inclusion cyst, dermatofibroma,Herbenden's node, angioleiomyoma should be consideredin a differential diagnosis if there is any are two types of digital mucoid cysts thathave a similar clinical appearance however they aredifferent in both location and etiology. These cysticnodules or papules can occur periungually or over thedistal interphalangeal joint. The most common tFpegenerally arises from the interphalangeal joint of the toeby herniation of the tendon sheath or joint other cause results from localized fibroblastic prolif-eration near the proximal nail fold and is not connectedto the joint space or tendon sheath (Figure 1).

3 ''6''These lesions are usually asymptomatic althoughwhen the cysts become larger more associated problemsarise. Usually, the Iarger lesions become painful secondaryto shoe pressure. Occasionaily the rysts also disturb nailgrowth. Nail dystrophies such as a longitudinal depressionor ridging may be noted on the adjacent nail condition is most common in middle aged andelderly parienrs and is very uncommon in young cysts are usually seen between the age of thirtyand eighty with a predilection for However,Calder et al did describe one patient who was 16 yearsold.' Historically the great toe has been described as themost common location for these lesions although twolarge retrospective studies discussing these lesions on theFigure 18. A classic digital rnucoid cyst in the periungual region ofthe hallux274 CHAPTER46feet noted a much greater incidence in the second andthird toes.'5'6 The etiology is unknown although traumaand arthritic changes have been implemented.

4 ''- Theauthor believes osteoarthritic changes in the distal inter-phalangeal joint are an inciting factor for this type oflesion (Figure 2). The pathogenesis of these lesions hasbeen linked to an alteration of fibroblast function fromthe usual production of collagen to mucin (hyaluronicacid). The histology reveals an increased number ofirregular angulated stellate-shaped fibroblasts dispersed ina mla(omatous stroma with basophiiic amorphousreplacement of dermal collagen.' Skin overlying thesecysts can be quite thin at times and they may modalities have been described as auseful tool for the study of these lesions. Digital mucoidcysts are spherical fluid filled structures that have a welldefined wall. Differentiating the origination of the cystcan be accomplished with the Newmeyer test whichentails injecting radiopaque dye into the interphalangealjoint and then observing if the cyst fi1ls on a the cyst fills there is an extension into the , ultrasound has been described as beneficial indifferentiating these lesions in the hand from other softtissue pathology such as tenosynovitis and pigmentedvillonodular synovitis.)

5 ' Magnetic resonance imaging alsoprovides clarification and insight of the pathophysiologyof digital mucoid cysts. Drape et al reviewed MR findingsin 23 patients with digital mucoid cysts. A,ll lesions werenoted to have a high signal intensity and sharp border onT2-weighted images. Of the 23 patients 19 (83olo) hadcysts with pedicles that extended to the distal inter-phalangeal joint. Osteoarthritis of the interphalangealjoint was noted in 16 patients (70o/o). Intracystic septaFigure 2A. An arthritic DIPJ with an overlving digital mucoid cyst that present in nine patients (39o/o). A few of the cystswere independent of the joint and had a polymorphicappearance extending beneath the nail variety of treatment opdons have been described.'r''"uTiaditionally, recurrence rates were very high for incisionaland injectional 'r3'r8 The greatest risk ofrecurrence is associated with simple puncture of the rystsince it minimally disturbs the dermal layer allowing the cystto reform within nvo months greater than 50 percent of thetime.

6 Attempts at multiple repeated punctures also fail withsimilar V{hen incised the ryst extrudes a thick, clear,jellyJike substance that tends to refil1 within two months(Figure 3). The use of cortisone has had no effect on the suc-cess of cyst drainage. More successful treatments have beendescribed. Draining the ryst foliowed by deroofing the lesionand cauterizing the base (electrodessication) is more efficientwith a recurrence rate of 40 percent although painful healingand scarring can be problematic." Sclerosing injections(4 percent alcohol) into the ryst reportedly dropped therecurrence rates to 30 has been described as an effective alter-ative method for treatment of digital mucoid cysts.'''aCryotherapy with liquid nitrogen is commonly used bydermatologists with success. Literature supports punctur-ing the cyst followed by the use of a double freeze thawcycle (FTC) due to the high rate of recurrence with singleFigure 2B. Close-up radiographic findings in the rrirh \rrhriris i.}

7 Omnron in interphalangeal joint mucoid ]APTER 46 275"*bslrl&EA .gw I k: ) ;*".;@*"fi,m ,H!'i*1&& .{ :l Y,frxffiG& * 1l:Wa ; *;rrY -/ :..'T1 ."t'Figure 3. Clear jellyJike substance can be drainedIiom these lesions. Simple puncture alone is a cesslul r rear ment " Two freeze thaw cycles are carried from the cyst allthe way to the transverse skin creases over the interpha-langeal joint. Each freeze time used is approximately 30seconds after the freeze (ice) field is established. A secondtreatment at least 4 minutes later is utilized for the doublefreeze cycle to increase the rate of success. Dawber et alnoted successful eradication of 12 out of 14 lesions with atwo to five year follow-up with the cryosurgical patient failed a second double freeze thaw cycle treat-ment and the other declined additional treatment. Therewas no significant post-cryosurgical morbidity andcosmetic outcomes were excellent without evidence ofscarring.'a Bohler-Sommeregger et al described a siighdydifferent technique.}

8 There were 7 recurrences of 19 cyststreated with an average recurrence time of monthsalthough six of the seven recurrences were single freezethaw cycles. Therefore they also recommended a doublefreeze thaw cycle. Their technique included puncturing thecyst followed by cryosurgery with liquid nitrogen until thefront extends 2 mm beyond the cyst then an approximate1 to 2 minute thaw followed by another treatment. Healingtime was approximately 21 to 30 days."Carbon dioxide laser has also been described as aneffective treatment at eliminating digital mucoid '20 Huerter et al noted successful elimination of ten lesionswith follow up ranging from 74 to 44 months." Karrer etal noted successful treatment in 4 of 6 cysts treated withcarbon dioxide laser. The recurrences occurred at 3 weeksand 11 months postoperatively. Their recommendationFigure 4. Schrudde transpositional and rotational skinflap lor either circular, oval or semicircular defects(redrawn from Dockeryl).

9 Was to avoid surgery until the simple laser treatment hadbeen performed since there was little morbidity and thepreliminary results were promising.'oComplete surgical excision (3 to 1 ellipse) of thelesion increases success rates above 70 Ingeneral, if the skin lesion is small and occurs directly overthe interphalangeal joint, a traditional 3:1 excisionalelliptical biopsy parallel with the transverse relaxed skintension lines should be performed, which allows exposureto the interphalangeal joint for arthroplasty and alsoeliminates redundant skin, therefore, increasing thestabiiity of the toe. Surgical excision with debridement ofbone (partial phalangectomy under the cyst) reportablyincreases success.'' Calder et al has reported successfulremoval of 14 of 15 mucous cysts on toes after 24 monthfollow up with simple excision of the lesion and jointdebridement without the use of skin flaps. A11 patientswere pleased with cosmetic appearance of their toe.

10 'However, osseous procedures will not address cysts in theperiungual areas. If the lesion is too large or is closer tothe nail piate, the tightness in the adjacent tissues requiresthe use of a Schrudde flap (slide swing rotational singlelobed flap). The Schrudde flap is a single lobed flap thatis a combination of a rotational and transpositional pedicle (base) has an incoming blood supply toinsure success. The combination transpositional androtational flap is ideal in that instance because itadequately distorts the skin leaving no direct communi-cation for the cyst to be re-estabiished (Figure 4). Three276 CHAPTER46modifications of the Schrudde flap exist ro correcrcirculag oval and semicircular defects..X/hen puckeringoccurs, a Burow's triangle can be cut ar rhe pivot pointalthough it should always be excised away from the flapnot to compromise the flap.'n The best overall trearmentresults come from complete excision of the cyst with bonedebridement of irregular joint osreophytes and arotational skin flap for closure.