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Intratendinous Epidermoid Cyst after Traumatic Penetration of Foreign Body: A Very Rare Case Report

Introduction: Intratendinous epidermal cysts are extremely rare soft-tissue lesions. Apart from traumatic occasions which are usually painful, in asymptomatic cases, they can be easily overlooked. The purpose of our study was to report the formation of an intratendinous epidermoid cyst after traumatic penetration and irritation of a wooden foreign body. Case Report: A 79-year-old man proceeded in the emergency department, with a skin cut in the dorsal side of the right hand from a sharp wooden segment. After surgical lavage and investigation for soft-tissue damages or subcutaneous foreign bodies, skin closure was performed. Ten months after trauma, the patient came again with persistent pain and limitation in range of motion of the ring finger. Ultrasonography demonstrated an intratendinous foreign body surrounded by the cystic lesion. Both the identified wooden fragment and the cyst, which were histopathologically verified as an epidermoid cyst, were removed. Conclusion: Clinicians should be aware that a tendon injury, along with chronic irritation from a foreign body, might result in the formation of an intratendinous epidermoid cyst.


Introduction
Epidermoid cysts are typically benign intradermal or subcutaneous tumors which are most commonly diagnosed in scalp, face, trunk, and extremities. They mostly regard hairbearing areas [1,2]. The occurrence of these cysts in anatomic regions without hair could be attributed to implantation and the proliferation of squamous epithelium into the dermis after trauma [1,2].

Case Report
A 79-year-old man proceeded in the emergency department with skin cut 2 x 1.5 cm in the dorsal side of the right hand from a sharp wooden segment during logging. After surgical lavage and exploration for soft-tissue damages or subcutaneous foreign bodies (under local anesthesia), it was found that both the extensor digitorum tendons and the neurovascular structures of the dorsal hand were intact. No foreign body was identified.
The thickness of the cyst wall was measured around 0.2 cm. Afterward, a cyst incision revealed the existence of a small wooden piece, which was removed along with the cystic layer (Fig. 3).
The accelerated rehabilitation protocol included passive RoM of the involved finger for 10 days followed by progressive active mobilization for another 2 weeks. Three weeks postoperatively, the patient was free of symptoms without any functional deficits, managing to fully restore the normal RoM, and return to proinjury daily activities.

Discussion
Ten months after the initial injury, the patient visited again the orthopedic department displaying limitation in the range of motion (RoM) of the right ring finger and persistent deteriorating pain, both in extension and flexion. The clinical examination demonstrated a palpable mass at the route of the common ex tensor tendon of the four th f inger. An ultrasonographic (U/S) evaluation revealed the presence of a well-defined hypoechoic cystic mass within the tendon, surrounding an echogenic lesion 0.6 x 0.2 cm, presumably intratendinous foreign body.
The most important finding of our study was that it presented the first-ever reported case of an intratendinous epidermal cyst caused by the existence of a foreign body after trauma. There is one sole similar article reported by O'Hara and Stone [8], demonstrating the appearance of intratendinous epidermoid cyst after tendon traumatic damage. Concerning our case, the intratendinous epidermal cyst was caused by another extremely rare entity, the intratendinous penetration, and maintenance of foreign material [9].
Two weeks postoperatively, following sutures removal, there was no sign of local pain, skin irritation, edema, or inflammation. However, 2 months post-traumatically, the patient returned to the hospital with mild pain and local swelling over the traumatized area. No neurovascular or functional deficits were diagnosed. Laboratory tests did not reveal any sign of infection, while the X-ray control was negative for bone lesions or the existence of foreign bodies. The patient was treated with non-steroidal anti-inflammatory drugs for 5 days. One week later, the patient was almost free of symptoms.
Thus, a skin closure with polypropylene non-absorbable sutures was performed. Antitetanic serum injection at once and antibiotics (cefuroxime 500 mg) for 7 days was given to the patient.
A surgical investigation was executed, initially with a longitudinal skin incision just above the U/S finding. No sign of any tendon inflammation was observed. Taking care not to critically damage the tendon, a longitudinal incision on the dorsal surface of the tendon was carried out. An intratendinous cystic lesion was revealed (Fig. 1, 2).
The dimensions of the foreign body were identical with those of the pre-operative sonographic measurement. As the last step, the tendon was carefully repaired, and trauma was closed in layers. The post-operative histopathological examination illustrated the presence of a cyst filled with keratinous material and lined with stratified non-keratinized squamous epithelium diagnosed as an epidermoid cyst.
The most frequent intratendinous cystic lesions are ganglionic cysts, which originate within the tendon substance itself and cause soft-tissue swelling [13,14]. They are thought to develop from the mucoid degeneration of connective tissue caused by chronic irritation or chronic repetitive injury [2,3,4,5].
Soft-tissue penetration of foreign bodies is commonly the outcome of laceration injuries [10]. Foreign material in tendons can be organic, wood, glass, metal, plastic, or gravel [9,10]. They can be asymptomatic and undiagnosed [10] or they are likely to cause problems such as purulent tendonitis, fibrosis, peritendinitis, foreign body granuloma, infection, calcification, or necrosis [9]. If we exclude metal foreign bodies, most of the other materials are radiolucent, a fact that makes their detection relatively difficult [10]. In such cases, a high-resolution, realtime U/S as a non-invasive, non-radiated, low-cost technique can accurately localize the foreign material with a sensitivity and specificity of more than 90% [11,12].

Conclusion
Regarding the formed intratendinous epidermoid cyst, its etiology is unclear and cannot be attributed to certain causes. The only O'Hara and Stone had correlated the formation of these lesions with trauma [8]. Similarly, in our case, tendon injury, along with chronic irritation from the foreign body, might be associated with the formation of the cyst, which entrenched the wooden remnant. On the other hand, when there is no traumatic history, the occurrence of intratendinous epidermal cysts might be connected to the congenital anomaly [6,15]. As presented in our case, these cysts might be painful or interfere with mechanical symptoms, and their removal usually leads to resolution of the symptoms [6,8,15].
Intratendinous epidermoid cysts are very rare soft-tissue lesions, which can be the outcome of overlooked intratendinous foreign bodies. Clinicians should be aware that a tendon injury, along with chronic irritation from a foreign body, might result in the formation of an intratendinous epidermoid cyst.