Neurology

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12 year old with progressive neurologic sx

Dx= dermoid
Ddx=    - epidermoid

T1 weighted images show Hyperintense suprasellar mass (arrow) that extends into and enlarges the left choroidal fissure. Hyperintensity suggest possibilities of fat, hemorrhage, and proteinaceous debris on unenhanced images

Axial proton density weighted image shows mild chemical shift artifact (c), further suggesting presence of fat
Aixal T1-weighted image with fat supperssion (D) confirms presence of fat within extraaxial lesion
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  • Epidermoid/ Dermoid Tumors
  • Epidermoid and dermoid tumors are non- neoplastic developmental masses that are derived from ectodermal rests. They may aptly be described as ectodermal heterotopias. Although the composition of epidermoids is essentailly of squamous epithelium, dermoids may contain more differentiated epithelial components such as sebaceous or sweat glands and hair follicles and may contain lipoid debris from squamous decomposition. This definition is in contrast to the traditional view that dermoids contain mesodermal elements. Both epidermoids and dermoids are of entirely ectodermal origin.
  • Congenital epidermoids and dermoids arise from abnormal inclusions of ectoderm resulting from improper disjunction of the neural tube from the cutaneous ectoderm during the third or forth week of gestation. Both lesions maybe associated with dermal sinuses and osseous defects. A very small subset of epidermoid (and possibly dermoid) tumors are not developmental in origin but rather are the result of traumatic implantation or iatrogenic (surgery lumbar puncture, etc.) inclusion of epidermal elements. These posttraumatic epidermoids tend to be more common in the spine, although they may occur intracranially as well.
  • In contrast to epidermoid cyst, dermoids tend to show less variability in their location. They are usually situated in the midline and most often involve the basal surface of the brain. Unlike epidermoids, dermoids tend to be circumscribed. A dermal sinus tract is often present in the adjacent soft tissues and should be diligently sought. Associated midline anomalies such as callosal hypo genesis are common and maybe a clue to the diagnosis.
  • On CT, dermoids exhibit markedly decreased attenuation due to the fatty nature of the tumor. Calcification maybe seen in the wall of the lesion (55,56). An osseous defect maybe present at the site of the sinus tract. When a dermoid is discovered, dedicated attention should be paid to the CSF spaces, because small fatty droplets maybe seen easily overlooked. In particular, fat droplets maybe seen “floating” within the frontal horns on axial or sagittal images of supine patients. These findings indicate rupture of the dermoid into the ventricular subarachnoid space. On MR, dermoide may exhibit heterogeneous signal, but most dermoids exhibit some component of high signal on T1- weighted images representing the fat content. Fat suppression sequences maybe useful (57), although not all dermoids will suppress. Chemical shift artifact maybe present. The primary differential diagnosis is teratoma or lipoma. If contrast enhancement is noted centrally, teratoma is more likely, however, rim enhancement has been observed in the setting of superimposed infection.

 

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