Imaging of skull base pathologies: Role of advanced magnetic resonance imaging techniques

Abstract

Imaging plays a vital role in evaluation of skull base pathologies as this region is not directly accessible for clinical evaluation. Computerized tomography (CT) and magnetic resonance imaging (MRI) have played complementary roles in the diagnosis of the various neoplastic and non-neoplastic lesions of the skull base. However, CT and conventional MRI may at times be insufficient to correctly pinpoint the accurate diagnosis. Advanced MRI techniques, though difficult to apply in the skull base region, in conjunction with CT and conventional MRI can however help in improving the diagnostic accuracy. This article aims to highlight the importance of advanced MRI techniques like diffusion-weighted imaging, susceptibility-weighted imaging, perfusion-weighted imaging, and MR spectroscopy in differentiation of various lesions involving the skull base.

Keywords: Skull base; diffusion-weighted imaging; magnetic resonance imaging; magnetic resonance spectroscopy; perfusion-weighted imaging; susceptibility-weighted imaging.

Figure 1.

Left paracavernous meningioma. A T2 hyperintense lesion in left cavernous sinus region extending into posterior fossa via Meckel’s cave into prepontine and left cerebellopontine angle cistern. Lesion reveals varied FA values in different part of lesion. High perfusion differentiated it from other diagnosis like schwannomas.

Figure 2.

Aspergilloma. A well-marginated extra-axial lesion based on right sphenoid wing which is mildly hyperintense on T1, markedly hyperintense on T2 with perilesional edema and contrast enhancement. T2* perfusion reveals lesion to be hypoperfused. Marked T2 hypointensity and low perfusion are pointers towards a granuloma.

Figure 3.

Left middle cranial fossa paracavernous lesion. Low T2 signal and low ADC values indicate high cellularity. Contrast enhancement with low perfusion seen. High cellularity and low perfusion supports the final HPE diagnosis of plasmacytoma.

Figure 4.

Paraganglioma. An intensely enhancing right jugular fossa mass. Very high perfusion supports the diagnosis of glomus jugulare paragangliomas.

Figure 5.

Schwannoma. A heterogeneous enhancing T2 hyperintense extra-axial lesion seen in middle and posterior cranial fossa on right side extending via foramen ovale in the infratemporal fossa, along the mandibular nerve. Multiple microbleeds on SWI and low perfusion support the diagnosis of schwannoma and are of great value in characterization of less typical lesions.

Figure 6.

Endolymphatic sac tumor. A left cerebellopontine angle mass with bony destruction. T1 hyperintensities and increased perfusion suggest the diagnosis of endolymphatic sac tumor apart from the location of the lesion.

Figure 7.

Cholesteatoma. Left petrous T1 isointense lesion with CT revealing bony destruction with marginal sclerosis. Presence of diffusion restriction with low ADC values helped to arrive at the diagnosis of cholesteatoma. Mild peripheral contrast enhancement is also noted in this case.

Figure 8.

Cholesterol granuloma Left petrous lesion hyperintense on both T1 & T2 with no diffusion restriction or significant contrast enhancement.

Figure 9.

Right petroclival lesion with bony destruction, punctuate calcifications and contrast enhancement. High facilitated ADC and low perfusion favor the diagnosis of chondromatous lesion.

Figure 10.

Rosai–Dorfman disease. Right paracavernous lesion which is T1 hypointense, markedly T2 hypointense with mild diffuse blooming on SWI and showing homogenous contrast enhancement.

Figure 11.

Cavernous hemangioma. A right para cavernous lesion hypointense on T1, brightly hyperintense on T2 with facilitated diffusion and low perfusion. Dynamic T1 contrast enhanced scans reveals initial central enhancement with progressive centrifugal enhancement. Delayed images reveal intense homogenous enhancement.

Figure 12.

An expansile osteolytic lesion involving the right sphenoid wing. T2WI reveals the lesion to be mildly hyperintense. Constructive interference in steady state (CISS) images delineate the relation with the orbit. Lesion reveals intense contrast enhancement with very high perfusion. Work up had revealed a thyroid nodule. Case of hypervascular metastases from follicular thyroid carcinoma.