1. Background and Importance
pidermoid cysts are rare tumors of spinal cord. Less than (1%) of all spinal cord tumors are epidermoid cysts [1], which are usually located as intradural and extramedullary and are products of developmental problems [2]. Sometimes they are iatrogenic [3]. As most of the reported cases are in thoracic and lumbar areas, there are few cases concerning thoracic intramedullary epidermoid cysts. Here, we report a case of small intramedullary epidermoid cyst in a 40 year-old woman.
2. Case Presentation
A forty-two year-old woman was referred to our clinic for radicular pain and weakness in left extremity. The patient had no other complaints. Physical examinations including neurological examination of cranial nerves and upper extremities were normal. Hyperactive reflexes and spasticity of the lower extremities were noted. Bilateral Babinski responses were elicited. The muscle strength of the lower extremities was diminished, especially in distal muscles and the weakness was more in the left in contrast to the right side of the body. No definite sensory level was found. A sense of position and vibratory sensations were preserved. The anal reflex was normal.
On lumbosacral MRI, a left paracentral L5-S1 disk protrusion was seen; however, it could not justify the symptoms on her right lower extremity. Therefore, MRI of cervical and thoracic spines were requested. Cervical MRI findings were normal. Thoracic MRI illustrated a focal fusiform enlargement of the thoracic cord at T4 and T5. On sagittal images, hypointensive and hyperintensive intramedullary lesions at T4 level were seen on T1 and T2-weighted images, respectively (figure 1 A & B, figure 2). The cord above and below this cavity tapered down to a normal diameter and did not show abnormal signal. The lesion did not show any enhancement in MRI with gadolinium (figure 1 C).

Operative Approach
A laminectomy (T3-T5) was performed and no evidence of dysraphism such as a dermal sinus, was found. When the dura was opened, the cord appeared distended (figure 3 A). Under the operating microscope, the posterior median raphe was obliterated and the midline was identified at the midpoint between the dorsal root entry zones. A 1.5-cm myelotomy centered over the lesion was performed (figure 3 B). There was an avascular mass lying completely within the cord immediately beneath the surface. Pia traction sutures were used to open the myelotomy incision and expose the intramedullary tumor. The mass consisted of a white, waxy, and flaky material with no apparent skin appendages. The tumor was gradually and completely removed and the cord was decompressed. No attempt was made to remove the lining of the cyst since it was firmly attached to the substance of the cord.

The material was sent to a pathologist and the diagnosis of epidermoid cyst was confirmed (figure 4). The patient was visited two weeks later and no symptoms in the left side of the body were seen. The MRI of the brain was normal with no sign of myelin degenerative diseases like multiple sclerosis. 

3. Discussion
Less than (1%) of intraspinal tumors are epidermoid cysts. These benign tumors are very rare with cranial to spinal ratio of 14:1 [4]. Pure intramedullary epidermoid cycts are rare and only 32 cases of intramedullary cysts in thoracic cord are reported (table 1). Epidermoid cyst is the result of incomplete cleavage of the neural ectoderm from cutaneous ectoderm within the third to fifth week of gestation [5]. It is usually a developmental problem but iatrogenic cases due to implanting epidermal cells by repetitive lumbar puncture are also reported [3]. MRI is the diagnostic measure to detect the cyst with absence of peri-tumor edema and sharp borders differentiating tumor from normal tissue [6]. The preferred treatment of epidermoid cyst is complete removal. however there is a report of several recurrences in the same location [7]. Although these tumors are essentially considered benign, malignant transformation might be seen [8].

In our patient, the small epidermoid cyst at T4 was the culprit causing symptoms. The epidermoid cyst may be accompanied by a dermal lesion, which was absent in our case. After surgery, the patient was symptom free as the pressure on the cord was removed. In an 18-month follow-up, no symptom was seen.
In patients with symptoms and signs of upper and lower motor neuron, before labelling the patient with a disease only according to brain MRI findings, a careful imaging study of the spinal cord might be reasonable. In other words, lesions in thoracic region of the spinal cord are usually neglected because of another lesion in the lumbosacral imaging that might justify the symptoms. As in our case, a small intramedullary lesion can mimic the signs and symptoms of more serious diseases like multiple sclerosis. The small size of tumor in our patient and normal skin over the thoracic cord in concert with few neurologic symptoms which were to some degree justified by patient’s brain MRI had led to misdiagnosis of the condition. 
Review of the Literature
Review of the literature was performedusing PubMed database by searching for the following combinations: “Epidermoid cyst” AND “spinal cord”. The search was limited to humans and articles reported in English. No restriction was set regarding the type of publication, the publication date, or publication status. The search was broadened extensively cross-checking the reference lists of all retrieved articles fulfilling the aim of the study. For all databases, the latest date of search was run on 2018.
Thirty-two cases of reports belonged to years of publication from 1965 to 2018. Table 1 lists all of the cases reported in the literature with epidermoid cyst” and  “spinal cord”. the patient's age ranged from 16 months to 74 years old. one patient presented with fever and recurrent upper respiratory tract infection [16]. two patients presented with sudden paresia [9, 19]. Twenty-eight cases of 32 progressive paraparesia were observed. Back pain was observed in seven cases [10, 11, 15, 19, 20, 22, 26].
In two cases, clinical symptoms occurred in less than three years [9, 16, 31]. They were often referred to a clinic with more severe symptoms and abrupt onset symptoms. In 17 of 32 cases (53%), urinary tract symptoms such as urinary incontinence and bladder disorders were observed. in one patient, the only symptom was recurrent urinary tract infection and incontinency [25]. All cases of involvement included the thoracic area in the imaging. In 20 patients (62.5%) of cases, the onset of the complications was reported to be at least Six months. In two patients, thoracic intramedullary epidermoid cysts coexisted with sinus dermal tract diagnosed before reaching theee years old of age whereas in one history of meningocele, surgery in thoracic region was reported [35].
In 19 patients, the total resection of tumor with tumor capsule excision were achieved but in 13 patients the capsules were adherent to spinal cord and partial resection of capsule was performed. Tree patients (8, 16, 34) underwent second surgery for tumor recurrent. in two of them, subtotal resection of tumor was done because of capsule adhesion to spinal cord [16, 34]. One patient with malignant transformation of epidermoid cyst was reported [8].
4. Conclusion
Spinal intramedullary epidermoid cysts are rare tumors without specific clinical presentation. The recognition of epidermoid cysts in the pediatric age group is important. There may be associated congenital anomalies which need to be carefully sought as an aid to diagnosis. Early diagnosis can be done by MRI. Surgical excision is the treatment of choice and the overall outcome of these lesions is good, even if they present with a ruptured cyst, as was the case with our patient. 

Ethical Considerations
Compliance with ethical guidelines
All ethical principles were considered in this article. The participants were informed about the purpose of the research and its implementation stages; they were also assured about the confidentiality of their information; Moreover, They were allowed to leave the study whenever they wish, and if desired, the results of the research would be available to them.
Funding
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
Authors contributions
All authors contributed in preparing this article.
Conflict of interest
The authors declared no conflict of interest. 

References