Abstract
Intracranial dermoid cysts are rare congenital lesions resulting from the inclusion of ectodermal cells during the closure of the neural tube, which occurs between the third and fifth gestational week. They may be associated with dermal sinus tracts and other neural tube closure defects, although they are usually not present in the sellar region. The cyst wall is made of connective tissue, and they are filled with a heterogeneous mixture of fat, hair, dystrophic calcifications or teeth, and fatty products of sebaceous glands. The cyst growth results from the accumulation of these glandular secretions and epithelial desquamation. Dermoid cysts are intradural extra-axial lesions that tend to occur on the midline and particularly in the sellar/parasellar region. Exceptional extradural locations have also been reported, especially within the cavernous sinus. Common clinical symptoms include headaches, seizures, and suprasellar dermoid cysts which often present with visual disturbances. Dermoid cysts are also well-known to cause chemical meningitis when they rupture and spill their content in the subarachnoid cisterns. Hydrocephalus is a rare presentation, and is subsequent to the trapping of the ventricular system rather than aseptic meningitis.
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Intracranial dermoid cysts are rare congenital lesions resulting from the inclusion of ectodermal cells during the closure of the neural tube, which occurs between the third and fifth gestational week. They may be associated with dermal sinus tracts and other neural tube closure defects, although they are usually not present in the sellar region. The cyst wall is made of connective tissue, and they are filled with a heterogeneous mixture of fat, hair, dystrophic calcifications or teeth, and fatty products of sebaceous glands. The cyst growth results from the accumulation of these glandular secretions and epithelial desquamation. Dermoid cysts are intradural extra-axial lesions that tend to occur on the midline and particularly in the sellar/parasellar region. Exceptional extradural locations have also been reported, especially within the cavernous sinus. Common clinical symptoms include headaches, seizures, and suprasellar dermoid cysts often present with visual disturbances. Dermoid cysts are also well-known to cause chemical meningitis when they rupture and spill their content in the subarachnoid cisterns. Hydrocephalus is a rare presentation, and is subsequent to the trapping of the ventricular system rather than aseptic meningitis.
At imaging, a dermoid cyst appears as a well-circumscribed, fatty round mass with a peripheral capsule that may enhance or harbor calcifications. They are hypodense on CT, and possibly contain calcifications or teeth (Fig. 50.1). At MRI, dermoid cysts appear with characteristic fatty signal intensities on all sequences. Unlike lipomas, dermoid cysts are heterogeneous (Figs. 50.1 and 50.2) and have a capsule that may enhance (Fig. 50.2). The fatty content thus appears with T1- and T2-high signal intensities on spin-echo sequences, but demonstrate low GE T2 signal intensity. This point is crucial as it may mimic blood, like either a subacute parenchymal hematoma or a cavernoma. Therefore, T1WI with fat saturation is of precious help to confirm the fatty nature of the lesion and endorse the diagnosis of dermoid cyst when the lesion is heterogeneous (Figs. 50.1 and 50.4). Of course, in the absence of T1WI with fat saturation, one should consider that a simple nonenhanced CT scan easily demonstrates marked hypoattenuation in cases of fat and allows one to distinguish fatty from hemorrhagic lesions. Another clue to evoke the fatty origin of the signal is the presence of a chemical shift artifact that appears as a peripheral curvilinear hypointensity covering the lesion along the frequency-encoding direction (Fig. 50.3). In rare cases the fat floats on the rest of the liquid filling the cyst, giving a characteristic fat-fluid level, which we believe is pathognomonic of a dermoid cyst when observed in a well-defined intracranial lesion (Fig. 50.3). Finally, in cases of rupture in the subarachnoid space, the visualization of fatty T1-hyperintense droplets in the sulci or an anterior fat-fluid level in the ventricles is also highly suggestive of the diagnosis (Fig. 50.4).
Further Reading
Bonneville F, Cattin F, Marsot-Dupuch K et al (2006) T1 signal hyperintensity in the sellar region: spectrum of findings. Radiographics 26:93–113
Liu JK, Gottfried ON, Salzman KL et al (2008) Ruptured intracranial dermoid cysts: clinical, radiographic, and surgical features. Neurosurgery 62:377–384
Osborn AG, Preece MT (2006) Intracranial cysts: radiologic-pathologic correlation and imaging approach. Radiology 239:650–664
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Bonneville, F. (2016). Dermoid Cyst. In: MRI of the Pituitary Gland. Springer, Cham. https://doi.org/10.1007/978-3-319-29043-0_50
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DOI: https://doi.org/10.1007/978-3-319-29043-0_50
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