Giant epidermal cyst of the arm: a rare presentation

Abstract

A giant epidermal cyst is a benign soft tissue mass commonly involving the trunk, hand and face. The authors report a rare presentation of a 69-year-old man who presented with a painful, slow-growing left arm mass for 30 years duration. Examination revealed a large, mobile, soft tissue mass of the lateral aspect of the left arm. MRI showed a large, cystic left arm soft tissue mass. The mass was excised and the diagnosis of a giant epidermal cyst was made based on imaging and histopathology after surgical resection. The mass measured 9.5 cm x 8 cm x 4 cm, which is the largest reported giant epidermal cyst of the upper extremity.

Background

Epidermal cysts, which are also known as epidermoid cysts or epidermal inclusion cysts, are common benign cutaneous cysts.¹ An epidermal cyst may be classified as a giant epidermal cyst if it exceeds 5 cm. They arise from occluded pilosebaceous follicles or traumatic migration of epidermal cells into the dermis. They commonly occur on the face, base of the ears and trunk.^{2 3} Diagnosis is based on history, physical examination, imaging and histology.^{3 4} Epidermal cysts have been found in the gluteal region,^4–6 the foot,^{2 7 8} the perineum⁹ and the forearm.^{8 10} However, an epidermal cyst of the arm exceeding 5 cm is extremely rare and has not been reported in the literature. This case report describes a rare presentation of the largest reported giant epidermal cyst of the upper extremity reported in the literature.

Case presentation

A 69-year-old Caucasian man was referred to the hand surgery clinic by his primary care provider for the evaluation of a soft tissue mass in the left arm. The mass had been present for 30 years but had enlarged significantly over the previous few months. It was causing significant discomfort. Otherwise, he did not complain of any numbness, tingling or fevers. He denied weight loss or loss of appetite. His medical history was significant for neoplasm of the bladder and paroxysmal atrial fibrillation. He was a non-smoker and did not consume alcohol. He was retired. On physical examination, there was a large, mobile and subcutaneous mass in the left arm. The mass was soft and non-tender to palpation. The mass was estimated to be 12 cm x 15 cm on physical examination. There were no open wounds or erythema. The left upper extremity was neurovascularly intact, and his systemic examination was within normal limits.

Investigations

Radiographs of the left humerus and shoulder showed a radiopaque, well-circumscribed soft tissue mass of the left arm (figure 1). There was no mineralisation of the soft tissue mass on radiographs. There were no fractures or bony involvement. MRI of the left humerus with and without contrast showed a well-circumscribed soft tissue mass in the left arm (figures 2–6). The soft tissue mass was superficial to the fascia. It had a homogeneous low signal on T1 weighted images with a few high signal septations and debris. It had a homogeneous high signal on T2-weighted images with a few low signal septations and debris. There was a thin, smooth, peripheral enhancement on postcontrast imaging. There was no peritumoral oedema. The radiographs and MRI findings were consistent with a giant epidermal cyst of the left arm.

Figure 1.

A 69-year-old man with a giant epidermal cyst of the arm on this radiograph of the left humerus.

Figure 2.

A 69-year-old man with a soft tissue mass in the subcutaneous tissue of the lateral aspect of the arm that has an isointense signal to muscle on this axial T1-weighted MRI of the left humerus.

Figure 3.

A 69-year-old man with a soft tissue mass in the subcutaneous tissue of the lateral aspect of the arm that has a hyperintense signal on this coronal T2-weighted MRI.

Figure 4.

A 69-year-old man with a soft tissue mass in the subcutaneous tissue of the lateral aspect of the arm that has a hyperintense signal on this axial T2-weighted MRI.

Figure 5.

A 69-year-old man with a soft tissue mass in the subcutaneous tissue of the lateral aspect of the arm with a thin rim of peripheral enhancement on this axial T1-weighted fat-suppressed, post-contrast MRI.

Figure 6.

A 69-year-old man with a soft tissue mass in the subcutaneous tissue of the lateral aspect of the arm with a thin rim of peripheral enhancement on this coronal T1-weighted fat-suppressed, post-contrast MRI.

Treatment

The patient elected to undergo an open biopsy and marginal resection of the soft tissue mass. Five core needle biopsies were performed at the area that appeared to be most suspicious for malignancy on MRI. Clear fluid was expressed from each biopsy site. A pathologist analysed the frozen sections intraoperatively and there were no malignant cells present. The soft tissue mass was marginally excised. The mass measured 9.5 cm × 8 cm × 4 cm. Histopathology of the mass showed a smooth-walled cyst lined by stratified squamous epithelium with a granular layer filled with grey grumous material that histologically was keratin flakes (figure 7). These findings were diagnostic of an epidermal cyst.

Figure 7.

Histopathology of the mass shows a smooth-walled cyst lined by stratified squamous epithelium with a granular layer filled with grey grumous material that histologically is keratin flakes.

Outcome and follow-up

The patient returned to the clinic on postoperative day 10. His sutures were removed and his incision was clean, dry and intact. He was discharged from the clinic and instructed to follow-up on an as-needed basis.

Discussion

Epidermal cysts arise from occluded pilosebaceous follicles or traumatic migration of epidermal cells into the dermis.¹ As the epidermal cells proliferate and collect debris and keratin, a cystic space forms. They may also arise from residual ectodermal tissue during embryogenesis, human papilloma virus (HPV) or Gardner syndrome.⁴ In HPV, the theory is that plantar verruca warts on weight-bearing surfaces are pressed into the dermis, thus causing the cysts to form. Gardner syndrome should be on the differential if there are multiple epidermal cysts of the extremities.^{2 4}

Imaging for epidermal cysts usually show a subcutaneous, well-circumscribed soft tissue mass that is isointense or slightly higher signal intensity to normal muscle on T1-weighted MRI and high signal intensity on T2-weighted MRI. There is no enhancement on postcontrast MRI.⁸ Although epidermal cysts are benign and malignant transformation is rare, large cysts are concerning for possible malignancy. Malignancy should be ruled out by a biopsy.^{4 9} Histopathology for epidermal cysts typically shows a clear background, high cellularity, and nucleate and anucleate squamous cells. Keratinous material may be seen, but there is less when compared with other cellular elements.³

They may be treated with observation or surgical resection based on the patient’s symptoms. There is a 3% recurrence rate despite complete surgical excision of the cyst.⁵

Overall, epidermal cysts are common. Epidermal cysts of the upper extremity are usually found in the hand and <5 cm. Our case is a rare presentation of the largest reported giant epidermal cyst in the arm. It is important to rule out malignancy prior to definitive surgical resection.

Learning points.

• A giant epidermal cyst is a benign epidermal inclusion cyst >5 cm.

• They are commonly found in the gluteal region, perineum, face, foot, hand and forearm.

• Diagnosis can be obtained with radiographs and MRI prior to surgery.

• It is important to obtain a biopsy prior to surgical resection to rule out malignancy even though malignant transformation is rare.