Ruptured intracranial dermoid cysts: a pictorial review

Abstract

Intracranial dermoid cysts are rare, benign, congenital, slow-growing cystic lesions. They are composed of mature squamous epithelium and can contain apocrine, eccrine, and sebaceous glands as well as other exodermal structures. Rupture of intracranial dermoid cysts is a relatively uncommon phenomenon but can cause more serious complications such as chemical meningitis, vasospasm, and cerebral infarction. Understanding of the appearance of both unruptured and ruptured dermoid cysts on computed tomography and MRI, especially awareness of existing low signal "blooming artefacts" on certain sequences, aids diagnosis and referral to the proper specialty for appropriate treatment.

Keywords: blooming artefacts; dermatoid cyst; magnetic resonance imaging; rupture.

Figure 1

Unruptured dermoid cyst. A) Unenhanced axial computed tomography scan demonstrating a heterogenous predominantly fatty lesion with foci of peripheral calcification consistent with a dermoid cyst. B) Axial proton density-weighted images image confirms fatty nature of the lesion. C) Coronal T1-weighted image shows the lesion is suprasellar, and in the midline there is heterogenous internal structure with areas of high T1, representing fat, and isointense areas representing soft tissue/debris from dermoid epithelium. D) Coronal T2-weighted image; note the fat within the dermoid is higher in intensity than the adjacent cerebrospinal fluid. E-F) Pre and post-contrast sagittal T1-weighted images; there is no evidence of internal or rim enhancement to the dermoid cyst

Figure 2

Ruptured dermoid cyst. A) Unenhanced computed tomography demonstrating heterogenous predominantly fat density lesion adjacent to left medial temporal lobe. B) Multiple foci of subarachnoid fatty density lesions; appearances consistent with ruptured dermoid cyst. C-D) Axial T1-weighted images confirmed fat density lesion. E-F) Axial GRE T2-weighted image (haemosiderin sensitive sequence), heterogenous high and low T2 characteristics (an apparent blooming artefact). Axial T1-weighted imaging post-gadolinium without (G) and with fat suppression. (H) The internal components and subarachnoid foci become hypointense with fat suppression. I) Axial FLAIR and (J) fat-suppressed FLAIR demonstrating suppression of the internal fatty components; this can be a pitfall with the incorrect supposition that the internal component is predominantly fluid because it has become suppressed when in fact the lesion is fatty

Figure 3

Ruptured dermoid cyst. A) Axial T1-weighted image demonstrating a ruptured left frontal dermoid with diffuse subarachnoid fat. B) Axial T1-weighted image demonstrating a well-defined level in the middle of the left frontal lesion. The anterior part has a heterogenous component and the posterior part is homogenously hypointense, consistent with a fat fluid level. C) Sagittal T1-weighted image the fluid component lies posterior to the larger fatty component obeying the normal laws of gravity with the patient supine in the magnetic resonance imaging scanner. D) Axial T2-weighted image again demonstrating the fat fluid level; note that the fat is significantly brighter, and the posterior fluid level is similar in intensity to the cerebrospinal fluid space signal. E) Sagittal reconstruction from fat suppressed 3D FLAIR demonstrates suppression of the posterior fluid component, but also notice the fat suppression, which does not become as hypointense as the nulled fluid. F) Axial FLAIR suppression of posterior fluid component with no change in the anterior fat component

Figure 4

Differentiation of dermoid cysts. Pitfalls of susceptibility imaging. A-B) Axial GRE T2-weighted image (haemosiderin sensitive sequence), demonstrating a focal area of hypointensity in the left parafalcine position and in the quadrigeminal cistern. C-D) Axial T2-weighted image shows the quadrigeminal cistern lesion is heterogeneously hyperintense, and the parafalcine lesion is hypointense. E-F) Unenhanced computed tomography reveals the nature of the quadrigeminal lesion to be a lipoma and the parafalcine lesion to be a calcified meningioma

Figure 5

Differentiation of dermoid cysts. A) Sagittal T2-weighted image demonstrating multi-lobulated right temporal dermoid; note the chemical shift artefact and lesion extending superiorly within the parenchyma. B) Sagittal T1-weighted image with the most superior component with homogenous T1 characteristics consistent with predominantly liquid fat material. C) Axial fat suppressed FLAIR image with a homogenously hypointense left posterior temporal lesion; the lesion could easily be incorrectly mistaken for a fluid cyst. E-F) Diffusion-weighted image at B0 demonstrates complete low density with apparent blooming artefact; this could be mistaken for a haemosiderin-containing lesion