Skull Base, Petrous Apex, Infection Workup

Updated: Jun 22, 2020
  • Author: Andrea H Yeung, MD; Chief Editor: Arlen D Meyers, MD, MBA  more...
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Laboratory Studies

In cases of radiographically documented petrous apicitis, culturing middle ear effusions is important to help discern the microbiologic etiology and institute appropriate antibiotic therapy. This may be accomplished via paracentesis through an intact drum or culture of any purulent otorrhea.

Additional important lab studies include a complete blood count (CBC), electrolyte tests (eg, sodium, potassium, chloride), and a blood glucose determination.


Imaging Studies

See the list below:

  • Computed tomography (CT) scanning has replaced plain-film tomography as the standard diagnostic study for assessing skull base processes.

    • Temporal bone features diagnostic of petrous apicitis on CT scan include opacification of the mastoid air cell system, including the petrous apex; enhancement of the cavernous sinus; and bony erosion within the petrous apex. With contrast, cavernous sinus enhancement may also occur.

    • Acute petrositis may appear as an expanding lesion with irregular margins. In contrast, chronic petrous apicitis may demonstrate hypopneumatization and sclerosis.

  • Magnetic resonance imaging (MRI) provides additional important information unavailable with CT scanning.

    • In acute apicitis, a high-resolution MRI with gadolinium through the temporal bone demonstrates a low-intensity (ie, hypointense) signal on T1-weighted images, shows a high-intensity (ie, hyperintense) signal on T2-weighted images, and has ring enhancement with gadolinium dye.

    • In chronic apicitis, findings resemble chronic mastoiditis, showing a hyperintense signal on T2-weighted images. Some enhancement may occur with gadolinium, although not to the same degree as in acute apicitis.

    • These findings are key to diagnosis and help distinguish petrous apicitis from other lesions of the petrous apex, such as cholesterol granuloma (hyperintense on T1- and T2-weighted images, no gadolinium enhancement), cholesteatoma (hypointense on T1-weighted images, hyperintense on T2-weighted images, no gadolinium enhancement), and neoplasia (hypointense on T1-weighted images, hyperintense on T2-weighted images, and gadolinium enhancement).

  • Single-photon emission computed tomography (SPECT) scanning and nuclear imaging studies

    • SPECT scanning may be useful when CT scanning or MRI is nondiagnostic. SPECT scanning also can assist in identifying subtle petrous apex inflammation.

    • SPECT-scan findings in petrous apicitis include focal uptake of signal within the affected petrous apex.