Keywords carpal tunnel syndrome - carpal tunnel release - epidermal inclusion cyst
Carpal tunnel release is one of the most frequently performed surgical procedures
in the field of hand and upper extremity surgery and is known to be very effective
and safe, with low complication rates.[1 ]
[2 ]
[3 ] Reported complications include injuries to the recurrent motor branch and palmar
cutaneous branch of the median nerve, hypertrophic scar formation, pillar pain, laceration
of the superficial palmar arterial arch, incomplete release of the transverse carpal
ligament, tendon adhesion, wound infection, finger stiffness, and recurrence.[1 ] The percentages of structural complications to nerves, arteries, or tendons have
been reported to be less than 0.5%.[2 ]
Epidermal inclusion cysts can result from various surgical procedures that lead to
implantation of epidermal cells into deeper tissues under the dermis, but there are
few reports of postoperative occurrences of epidermal inclusion cysts in the hand
and wrist. To the best of our knowledge, an epidermal inclusion cyst caused by carpal
tunnel release has been described only once before.[4 ]
Here we describe a case of epidermal inclusion cyst that occurred after carpal tunnel
release. The aim of this report is to introduce this rare complication of carpal tunnel
release and emphasize the importance of basic surgical skills, such as gentle handling
of a surgical wound, profuse saline irrigation, and careful wound closure with precise
approximation of skin edges.
Case Report
A 44-year-old, right-handed man presented with a 1-year history of bilateral (left
hand greater than right hand) numbness and pain in the median nerve distribution.
Symptoms had aggravated in the 3 months prior to presentation. Electromyography and
nerve conduction studies indicated bilateral median neuropathies at the wrist with
more severe involvement of the left side. We performed mini-open carpal tunnel release
on the left side as usual, and the surgical wound was closed with vertical mattress
sutures of 3–0 nylon. The postoperative course was uneventful, and the patient stopped
follow-up visits with complete resolution of his symptoms 4 months after the surgery.
However, 20 months after surgery, he revisited with complaints of a palpable mass
at the previous operation site and a tingling sensation in the medial nerve distribution.
The mass grew insidiously, and he denied any traumatic episode involving the left
hand or wrist after the previous operation. Physical examination revealed a mass beneath
the previous operation scar ([Fig. 1 ]). The mass was palpable and firm without signs of infection and had a positive Tinel
sign. Ultrasonography demonstrated a 1.0 × 0.8-cm round, well-demarcated, irregular
echogenic soft tissue mass under the dermis ([Fig. 2 ]). We decided to perform surgical exploration and made a 2-cm skin incision along
the previous operation scar. A shiny, white, well-demarcated round mass was found
in the subcutaneous tissue layer ([Fig. 3 ]). The mass was easily pulled out. The wound was copiously irrigated and then closed
with vertical mattress sutures of 3–0 nylon. Histological examination confirmed the
diagnosis of an epidermal inclusion cyst ([Fig. 4 ]). The patient had an uneventful postoperative course, and his preoperative symptoms
disappeared. Six months following the excision, there was no evidence of recurrence
and the patient remained free of symptoms.
Fig. 1 Preoperative photographs showing an oval, firm, protruding mass on the scar of the
previous carpal tunnel release.
Fig. 2 Ultrasonography showing a round, well-demarcated, irregular echogenic mass under
the dermis.
Fig. 3 Intraoperative photographs showing a well-demarcated, round whitish yellow mass.
Fig. 4 Photomicrographs of biopsy specimen demonstrating stratified squamous cell epithelial
lining and eosinophilic keratin debris in the cystic cavity. (a ) Hematoxylin-eosin stain, magnification x10. (b ) Magnification × 100.
Discussion
Epidermal inclusion cysts, also known as epidermoid inclusion cysts, epidermal cysts,
epithelial cysts, keratin cysts, implantation cysts, infundibular cysts, or sebaceous
cysts, are unilocular cysts without septation that are encapsulated with fibrous tissue
and lined by true epidermis, which is stratified, keratinized squamous epithelium
with a granular layer as found on the skin surface and in the infundibulum of hair
follicles. Because these cysts do not involve sebaceous glands and do not contain
sebum, the term “sebaceous cyst” is a misnomer.[5 ] The cysts contain central, eosinophilic, keratinaceous material comprising accumulations
of cutaneous products, the debris of keratin, proteins, cholesterol, and cell membrane
lipids. The contents usually look like a chunk of cheese and have a foul smell. Cysts
can be skin-colored, yellow, or white and are usually slow-growing and asymptomatic.
However, polymicrobial infection of cysts with aerobic or anaerobic organisms may
occur, and malignant transformation, although very rare, has been reported.[6 ] Epidermal inclusion cysts are, strictly speaking, epidermoid cysts of traumatic
origin.[7 ] The proposed mechanisms of development of epidermoid cysts include incomplete cleavage
of cutaneous ectoderm at the embryonic stage, squamous metaplasia of the columnar
epithelial cells within dilated ducts, downward growth of epidermal cells with inflammation
after obstruction of the hair follicle, human papillomavirus infection, and growth
of implanted fragments of the epidermis within deep tissue after trauma or surgical
procedures.[4 ]
[5 ]
[8 ]
[9 ] Epidermoid cysts of nontraumatic origin are commonly located on hair-bearing areas
of the upper chest, upper back, neck or head, while epidermoid cysts of traumatic
origin—epidermal inclusion cysts—are more common on nonfollicular areas such as the
palms, soles, or buttocks.
Epidermal inclusion cysts are the third most common type of tumor of the hand, after
ganglion cysts and giant cell tumors of the tendon sheath.[10 ] They are more frequently seen in male manual laborers who are subject to repeated
minor trauma to the hand. They are usually located in the dermis or subcutaneous tissue
layer of the volar surface, especially the distal portion of the digits, as a solitary
lesion. However, multiple lesions and deep tissue involvement, such as tendon and
bone, have been reported also.[11 ]
[12 ] Lincoski et al[8 ] reported the largest series of epidermal inclusion cysts of the hand. They experienced
101 cysts (94 patients) among 623 hand tumors (16%) over a period of 27 years. Of
these patients, 83% were male and 56% were manual laborers. Mean age was 46 years
old. Forty-eight percent recalled a definite traumatic event prior to cyst development,
and three cases had cysts that occurred after prior unrelated surgery. However, detailed
information about the nature of previous operations was not provided. Seventy-two
cysts (71%) were located on the volar surface. Four cysts (0.04%) were intraosseous,
and four cases (0.04%) were multiple. There were 11 cases (11%) of recurrence. Lucas[13 ] also reported 58 patients (60 cases) with epidermal inclusion cysts of the hand.
In that study, 85% were male (49 patients), and 91% (53 patients) were manual laborers.
Forty-seven percent (27 patients) recalled a traumatic event. Cysts were intraosseous
in two patients (0.03%), and recurrence occurred in 10 patients (17%).
Although repeated minor trauma is a frequent cause of epidermal inclusion cysts in
the hand, postoperative occurrence of epidermal inclusion cysts in the hand has been
rarely reported. We found only two cases in the English-language medical literature.[4 ]
[14 ] One was due to dermofasciectomy and full-thickness skin graft to treat Dupuytren's
contracture,[14 ] while the other was due to mini-open carpal tunnel release.[4 ] Low et al[4 ] presented a case of epidermal inclusion cyst after carpal tunnel release and presumed
that subcuticular suture with braided polyglactin implanted epidermal tissue into
the deep tissue. In our case, we had closed the operation wound with vertical mattress
sutures of 3–0 monofilament nylon. It is therefore unclear how epidermal tissue was
implanted in our case.
As mentioned previously, all kinds of surgical and invasive procedures can induce
epidermal inclusion cysts. To prevent development of epidermal inclusion cysts, surgeons
should use a fresh, sharp scalpel and should be careful not to make invaginations
of skin edges.[7 ] Moreover, when sharp instruments or powered instruments are used, surgeons should
be careful not to push epithelium into the deeper tissues. Profuse irrigation of the
operation wound is also important to wash out epithelial debris.[7 ] Although carpal tunnel release is a relatively safe procedure and is widely performed,
surgeons have to keep in mind these recommendations to prevent the occurrence of epidermal
inclusion cysts.
