The Characteristic MR Findings of Spinal Cord Epidermoids
Written by Mingwang Zhu, M.D., Jianping Dai, M.D., Zhihua He, M.D.
July 10, 2001

Purpose:

Epidermoid cysts are a rare, slow growing benign tumor of the spinal cord which represent less than 1% of all intraspinal tumors⁽¹⁾. To our knowledge, only about 50 intramedullary epidermoid cysts have been reported in the literature and seven of them have been subjected to MR imaging. The radiological literature on spinal cord epidermoids is scarce, and the purpose of this study is to analyze the MR features of this rare lesion type.

Material and methods:

Eighteen patients (9-42 years of age, mean: 26.8 years) with pathologically proven spinal cord epidermoids were included in this study. All of the patients underwent MR study by a 1.5T or 0.5T MR imaging system. Sagittal T1-weighted images (T1WI, SE TE/TR: 16-25/300-550) and T2-weighted imaging (T2WI, FSE, TE/TR: 80-110/ 2400-3500) were obtained before injection of contrast agent. After intravenous injection of Gd-DTPA at a dose of 1ml/Kg body weight, the sagittal and axial T1-weighted images were obtained. Fat suppression was applied whenever the hyperintensity was found on the pre-contrast T1WI.

MR features of these tumors were analyzed with emphasis on tumor size, location, signal characteristics, and contrast enhancement. The secondary spinal cord changes and associated abnormalities of the spine were also inspected.

Results

In our experience, all spinal cord epidermoids were located at the lower end of the spinal cord around the conus and displayed relatively clear margins (89%). The extent of most tumors evaluated was smaller than the length of two vertebral columns (83%). On T1-weighted images, some tumors showed heterogeneous hypointensity (56%) (Fig 1), while others were isointense (33%) and hyperintense (11%). All tumors showed marked hyperintensity on T2WI. Eight of the tumors had isointense borders. The tumors in this group showed no contrast enhancement (Fig 2 & Fig 3) except for a minimal peripheral enhancement in 14 cases (78%) (Fig 1). Fat signal was demonstrated on T1WI in nine cases (Fig 2). No associated cyst formation, syrinx, and/or cord edema was found in the surrounding spinal cord. There were no secondary spinal cord changes in any of the cases and no associated spinal abnormalities were found either (Fig 1-3).

Discussion

Spinal cord epidermoid cysts can either be congenital, or acquired, such as the consequence of lumber puncture⁽²⁾. Congenital epidermoid cysts are believed to result from the inclusion of ectodermal tissue during the closure of the embryonic neural tube.

In the literature, the most frequent site of spinal cord epidermoid reported is in the thoracic region, and about 10% of cases displayed overlying bone and skin defects^(1,3-7). In our group, all cases were located around the conus, and no associated tissue abnomalities were demonstrated.

The MR appearance of spinal cord epidermoid cysts is generally characterized by heterogeneous signal intensity on the T1WI, an absence of secondary changes in the surrounding spinal cord, and no associated congenital abnormalities in the spine. In the contrast enhanced studies, minimal peripheral enhancement was occasionally found.

The most common differential diagnosis for spinal cord epidermoids includes spinal cord ependymoma or astrocytoma and other congenital lesions like dermoids and teratomas. The contrast enhanced study is very important for differentiating intramedullary epidermoid cysts from other lesions. Epidermoids show no contrast enhancement within the tumor; only minimal peripheral enhancement could be demonstrated. Some authors believe that the peripheral enhancement represents normal tissue reaction surrounding the tumor, while others considered it to represent an outer tumor wall composed of tumor cells. We believe it may be due to normal tissue reaction except in the cases of nodular enhancement as reported by Debray⁽⁴⁾.

Ependymoma is common at the conus, and may shows various degrees of contrast enhancement. Astrocytomas do not commonly occur at the conus, and are usually associated with contrast enhancement..

Considerable confusion exists in differentiating between dermoids and epidermoids. Frequently, only small portions of a dermoid contains skin appendages. This tissue may not be included in the biopsy specimen, and the result is that the dermoid cyst may be mistaken for an epidermoid.

Conclusion:

Spinal cord epidermoids have characteristic findings in MR studies. In our experience, spinal cord epidermoids occur predominantly around the lower end of the cord in young adult patients. The tumor tends to show heterogeneous hypointensity on T1WI and hyperintensity on T2WI. Other than a slight peripheral contrast enhancement, the tumor usually does not enhance in contrast studies.

References:

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