Benign Tumors of the Skull Base Workup

Updated: Mar 10, 2016
  • Author: Mario J Imola, MD, DDS, FRCS, FACS, FRCSC; Chief Editor: Arlen D Meyers, MD, MBA  more...
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Workup

Imaging Studies

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  • Diagnostic imaging is the most important component of an adequate workup following clinical assessment. CT scanning and MRI are complementary modalities in diagnosis and delineation of tumor extension. In certain circumstances, diagnostic imaging can accurately predict whether a tumor is benign or malignant and can narrow differential diagnoses.

  • CT scanning details bony structures, foramina, canals, and osteogenic lesions. Obtain contrast-enhanced axial and coronal 3-mm sections with bone and soft tissue window algorithms.

  • MRI has recently evolved into the single most useful imaging study of the skull base and provides highly accurate representation of soft tissue structures. Axial, coronal, and sagittal 3-mm sections with gadolinium enhancement are recommended using both T1- and T2-weighted modalities. T1-weighted images are not fat-suppressed; hence, adipose-containing structures are very bright, whereas structures containing water (eg, CSF) are dark. T2-weighted images are fat-suppressed, so fatty structures are dark and water is very bright. In both weightings, bone is visible as a very dark signal void, and muscle is of intermediate intensity. Tumor appearance varies depending on the histologic type and grade.

  • Angiography is indicated in selected tumors suspected of being hypervascular, (eg, hemangiomas, angiofibromas, glomus tumors, arteriovenous malformations, aneurysms). MR angiography is a good noninvasive technique but does not provide the detail of conventional intra-arterial angiography. When surgical resection is indicated, angiography combined with interventional preoperative embolization can be used to occlude the blood supply to vascular neoplasms, which possibly limits blood loss during subsequent surgery. [8]

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Diagnostic Procedures

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  • Biopsy is the only diagnostic technique that allows tissue diagnosis of skull base tumors. In many cases, the clinical presentation and diagnostic imaging provide sufficient information upon which to base a treatment decision. Because surgical excision is the treatment of choice for the vast majority of benign skull base tumors, a histologic tissue diagnosis is unnecessary prior to definitive resection. However, an attempt at biopsy is indicated for cases in which diagnostic imaging has not sufficiently narrowed the diagnostic possibilities, in very slow-growing lesions for which observation is contemplated, or when the patient is not a good surgical candidate.

  • Depending on the tumor location, both open biopsy and needle biopsy have indications. Open biopsy of tumors manifesting with palpable masses close to the surface can be approached through a simple skin incision. Biopsy of sinonasal masses can be performed with endoscopic guidance. Needle aspiration biopsy using either CT or MRI guidance can be used to safely biopsy deeper skull base tumors.

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