2009, Cilt 22, Sayı 3, Sayfa(lar) 237-239
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GIANT EPIDERMAL CYST OF THE FOREARM
Elif Karadeli1, Esra Meltem Kayahan Ulu1, Ahmet Fevzi Ozgur2, Emine Tosun3
1Başkent Üniversitesi Tıp Fakültesi, Radyoloji Ana Bilim Dalı, Ankara, Türkiye
2Başkent Üniversitesi Tıp Fakültesi, Ortopedi ve Travmatoloji Ana Bilim Dalı, Ankara, Türkiye
3Başkent Üniversitesi Tıp Fakültesi, Patoloji Ana Bilim Dalı, Ankara, Türkiye
Keywords: Forearm, Giant epidermal cyst, MRI
Abstract
An epidermoid cyst is a benign, intradermal subcutaneous soft tissue tumor. Subcutaneous epidermal cysts commonly involve the scalp, face, neck, trunk and back: fewer than 10 % occur in the extremities. We reported clinical, magnetic resonance imaging (MRI) and pathologic findings of a big epidermal cyst in the forearm.
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  • Abstract
  • Introduction
  • Case Presentation
  • Disscussion
  • References
  • Introduction
    An epidermoid cyst is a benign, intradermal subcutaneous soft tissue tumor. The tumor is considered to be a migration of an epidermal component into the dermis1. The diagnosis is clinical without imaging. Subcutaneous epidermal cysts commonly involve the scalp, face, neck, trunk and back: fewer than 10 % occur in the extremities2. We reported clinical, magnetic resonance imaging (MRI) and pathologic findings of a big epidermal cyst in the forearm.
  • Top
  • Abstract
  • Introduction
  • Case Presentation
  • Disscussion
  • References
  • Case Presentation
    A 30-year-old man presented with a right forearm mass, which had been slowly growing for 5 years. The patient had no trauma or pain. Physical examination demonstrated a big, firm, subcutaneous mass of the right forearm (Figure 1). In ultrasonographic examination, the tumor had a regular contour, and was heterogenously hypoechoic. Some vascularity was noted in the color Doppler sonography, mimicking a solid mass. Then, MRI was performed (1.5 Tesla, Philips Gyroscan) for detailed investigation. The MRI showed a large, well-defined, oval, homogeneous mass measuring 3.5x3x2 cm in diameter. The lesion was hypointense on T1- weighted images and hyperintense on T2- weighted images relative to the muscle. The lesion had some low signal intensity foci and serpiginous structures in it on T2-weighted images. After intravenous injection of gadolinium, there was no enhancement of the lesion (Figure 2). The excisional biopsy of the mass was performed under local anesthesia. The gross pathological examination showed that the mass was well-defined, nodular and cystic in nature. The histopathological examination showed that the lumen of the cyst was filled with keratin materials arranged in laminated layers. The wall of the cyst was composed of stratified squamous epithelium with keratohyalin granules (Figure 3). The pathologic diagnosis was keratinous cyst (epidermoid type).


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    Figure 1: A round lobulated mass in the forearm is evident.


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    Figure 2: MR imaging. Axial T1(A), T2(B), coronal T1(D) and fat supressed T2(E) images showed lobulated mass in the subcutaneous fat of the forearm, which had low signal intensity on T1 and high signal intensity on T2 images. Postcontrast axial T1(C) and fat suppressed T1(F) images show no enhancement of the tumor.


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    Figure 3: The histopathological examination showed that the lumen of cyst was filled with keratin materials arranged in laminated layers.

  • Top
  • Abstract
  • Introduction
  • Case Presentation
  • Disscussion
  • References
  • Discussion
    Epidermoid cysts probably occur from inflammation of pilosebaceous structures. The second theory is that the formation of an epidermoid cyst is related to the implantation of epidermis into the dermis through trauma (example: intramuscular injection) and migration during embryogenesis. A later theory frequently valid is for intracranial lesions3. The epidermoid cyst of our case is located on the forearm but the patient had no trauma or injection history. Lee et al4 showed the sonographic findings of epidermoid cysts, which can have lobulated contours and show color Doppler signals, mimicking a solid mass. Similar to his study we showed that the mass was not anechoic as a cyst, instead it was hypoechoic, heterogeneous and showed color Doppler signals as solid masses. Unfortunately, we did not record the ultrasonographicimages of our patient.

    Hong et al reported that MRI findings of unruptured epidermal cysts were hypointense on T1 and hyperintense on T2-weighted images relative to the muscle5. On postcontrast T1- weighted images, peripheral rim enhancement was seen. Epidermoid cysts may have hyperintense regions on T1-weighted images compared to muscle6, and may be hypointense on T1 and T2-weighted images related to dense debris and calcification components7. Shibata et al reported that no enhancement was observed inside the tumors and the variety of signal intensities on T1 and T2-weighted images reflects differences in chemical components of the epidermoid cysts2.

    Our case was hypointense on T1-weighted images, hyperintense on T2-weighted images compared to muscle. This case had a variable amount of serpiginous lower signal foci on T2- weighted images. We thought that heterogeneity on T2-weighted images related to the cyst lumen was filled with keratin arranged in laminated layers.

    The differential diagnosis of an epidermal cyst contains a fibrous tissue tumor, such as benign fibroma, xanthoma, malignant fibrous histiocytoma or fibrosarcoma, other subcutaneous cystic masses, vascular lesions, cystic degeneration and hemorrhage, lymphangioma with hemorrhage, cystic teratoma, large ganglion cyst and echinococcal cyst5,6 Ganglion cysts are hyperintense on T2-weighted images, and show peripheral rim enhancement on postcontrast images. The heterogeneous signals of epidermoid cysts on T2-weighted images may help differentiation of epidermal cysts from other fluid cysts (ganglion cyst, bursitis). Some solid tumors such as neurogenic tumors, nodular fasciitis, myxoid tumors may be hyperintense on T2-weighted images, so they mimic cystic masses. The enhancement pattern of these solid masses can be used to differentiate epidermal cysts5.

    In conclusion, an epidermal cyst should be thought in the differential diagnosis of a cystic soft tissue masses. Useful features for the diagnosis of an epidermoid cyst of the extremity are a well-defined border, round or oval lesion, subcutaneous location, hypointense on T1- weighted images, hypointense foci in the hyperintense background on T2- weighted images, and no enhancement on postcontrast images.

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  • Abstract
  • Introduction
  • Case Presentation
  • Discussion
  • References
  • References

    1) Shimizu Y, Sakita K, Arai E, et al. Clinicopathologic features of epidermal cysts of the sole: comparison with traditional epidermal cysts and trichilemmal cyst. J Cutan Pathol 2005, 32:280-285

    2) Shibata T, Hatori M, Satoh T, Ehara S, Kokubun S. Magnetic resonance imaging features of epidermoid cyst in the extremities. Arch Orthop Trauma Surg 2003; 123:239-241.

    3) Bostroem E. Ueber die pialen epidermoide, dermoide and duralen dermoide. Zentbl allg Path Anat 1897; 8:1-98.

    4) Lee HS, Joo KB, Song HT, et al. Relationship between sonographic and pathologic findings in epidermal inclusion cysts. J Clin Ultrasound 2001; 29: 374-383.

    5) Hong S, Chung H, Choi J, Koh Y, et al. MRI findings of subcutaneous epidermal cysts: Emphasis on the presence of rupture. AJR 2006; 186:961-966.

    6) Fujimoto T, Murakami K, Kashimada A, et al. Large epidermoid cyst involving the ischiorectal fossa: MR demonstration. Clin Imaging 1993; 17:146-148.

    7) Fu YT, Wang HH, Yang TH, et al. Epidermoid cysts of the testis: diagnosis by ultrasonography and magnetic resonance imaging resultin in organ-preserving surgery. Br J Urol 1996;78:116-118.

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  • Abstract
  • Introduction
  • Case Presentation
  • Discussion
  • References
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