Skull Base, Petrous Apex, Tumors Workup

Updated: Jul 18, 2018
  • Author: Michael J Fucci, MD; Chief Editor: Arlen D Meyers, MD, MBA  more...
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Workup

Laboratory Studies

No specific laboratory evaluation is indicated in petrous apex lesions. Leukocytosis is often seen with infectious lesions, but, otherwise, laboratory findings are not helpful.

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Imaging Studies

Imaging studies are the primary method used to diagnose these lesions. CT scanning is often the initial study used in evaluating the lesions. Contrast enhancement is helpful in the diagnosis, and its administration is recommended if no contraindications exist.

MRI provides valuable information in accurately diagnosing these lesions. The CT scan and MRI characteristics of each petrous apex lesion are outlined in Tables 1 and 2, respectively.

Table 1. Petrous Apex Lesion Characteristics on CT Scanning* (Open Table in a new window)

Lesion

Bone Erosion

Eroded Margin

Contralateral Apex

Contrast Enhancement

Cholesterol granuloma

+

Smooth

Highly pneumatized

-

Cholesteatoma

+

Smooth

Often not pneumatized

-

Petrous apicitis

+

Irregular

Variable

-

Effusion

-

-

Usually pneumatized

-

Bone marrow asymmetry

-

-

Variable

-

Carotid aneurysm

+

Smooth

Variable

+

Neoplasia

+

Variable

Variable

+

*From Jackler RK and Parker D: The radiographic differential diagnosis of petrous apex lesions. AJO 1992;13:561-574 [7]

Table 2. Petrous Apex Lesion Characteristics on MRI Scanning (Intensity Compared with Adjacent Brain)* (Open Table in a new window)

Lesion

T1 Images

T2 Images

T1-Gadolinium

Cholesteatoma

Hypo

Hyper

No enhancement

Cholesterol granuloma

Hyper

Markedly hyper

No enhancement

Petrous apicitis

Hypo

Hyper

Rim enhancement

Effusion

Hypo

Hyper

Mucosal enhancement

Bone marrow asymmetry

Hyper

Hypo

No enhancement

Neoplasia

Hypo

Hyper

Enhancing

Carotid aneurysm

Hypo

Mixed

Rim enhancement

*From Jackler RK and Parker D: The radiographic differential diagnosis of petrous apex lesions. AJO 1992;13:561-574 [7]

Preoperative angiography is required for suspected aneurysms. In rare cases, branches of the external carotid artery supply these lesions and preoperative embolization may be beneficial. The status of the internal carotid artery and vertebral-basilar systems are important in determining whether the carotid artery can be sacrificed. A balloon occlusion test is occasionally used to determine the neurologic status from a unilateral carotid occlusion.

Arteriography remains helpful in determining other lesions responsible for pulsatile tinnitus, such as glomus tumors.

MRI arteriography and venography determine dural sinus patency, although angiography remains the diagnostic criterion standard.

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Diagnostic Procedures

See the list below:

  • Imaging studies, including CT scanning and MRI, usually narrow the differential diagnosis. MRI venography and angiography help in defining vascular lesions.

  • Preoperative histologic diagnosis is difficult because safe access to tissue is nearly impossible.

  • Cultures and sensitivities in bacterial disorders are helpful and are obtained from discharge within the ear canal or through a myringotomy.

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Histologic Findings

Infectious lesions and inflammatory lesions

Petrous apicitis shows a white cell infiltrate consistent with an abscess.

Congenital and acquired cholesteatoma show sheets of stratified keratinizing squamous epithelium without evidence of abnormal mitosis. Granulation tissue and fibrosis often surround them.

Cholesterol granulomas represent a foreign body granulomatous response to cholesterol crystals arising secondary to hemorrhage. Poor ventilation facilitates accumulation of byproducts.

Mucoceles are cysts lined by pseudostratified ciliated columnar epithelium. Fibrosis, granulation tissue, hemorrhage, and squamous metaplasia are common.

Neoplastic lesions

Chordomas are malignant neoplasms arising from the embryonic remnants of the notochord. This pseudoencapsulated tumor contains cells that are epithelioid with vesicular nuclei and abundant cytoplasm that appears granular to vacuolated. Extensive vacuolization can appear as soap bubbles, compressing the nucleus and creating the classic physaliferous cells.

Chondrosarcomas are malignant tumors of cartilage with lobulated hypercellular areas characterized by hyperchromatic pleomorphic nuclei and prominent nucleoli.

Meningiomas are benign neoplasms arising from arachnoid cells. Four subgroups of meningiomas exist: syncytial or meningothelial, fibroblastic, transitional (both syncytial and fibroblastic), and angioblastic. The cells are whorled, and the nuclei have a punched out or empty appearance resulting from intranuclear cytoplasmic inclusions. Psammoma bodies are typical in meningothelial meningiomas.

Schwannomas are benign tumors arising from Schwann cells, typically on the eighth cranial nerve. Antoni A areas are composed of compact spindle cells, and Antoni B areas are composed of loose hypocellular areas. Most tumors have a mixture of both types. The nuclei are vesicular to hyperchromatic, elongated, and twisted with cells arranged in short interlacing fascicles. Whorling or palisading of nuclei is common.

Glomus tumors are benign and arise from the extra-adrenal neural crest paraganglia. Cell nests or zellballen patterns are characteristic of paragangliomas. Chief cells primarily compose the tumor, with uniform nuclei, dispersed chromatin, and abundant eosinophilic, granular, or vacuolated cytoplasm. Mitosis and necrosis are rare. The chief cells are argyrophilic, and reticulin staining delineates the cell nests.

Nasopharyngeal carcinoma arises from the surface epithelium of the nasopharynx. The World Health Organization subtypes these squamous cell tumors into 3 histologic variants: keratinizing, nonkeratinizing, and undifferentiated.

Keratinizing tumors represent 25% of all nasopharyngeal tumors. This is a classic squamous cell carcinoma often graded as well, moderately, and poorly differentiated.

Nonkeratinizing tumors represent 15% of all nasopharyngeal carcinomas. The growth pattern is similar to transitional cell carcinoma of the bladder. No desmoplastic response to tissue invasion occurs.

Undifferentiated tumors account for 60% of nasopharyngeal tumors. A syncytial growth pattern with oval or round vesicular nuclei, prominent eosinophilic nucleoli, scant cytoplasm, and increased mitosis is noted. Lymphoepithelioma is incorrectly diagnosed in some of these cases because of a significant nonneoplastic lymphoid composition.

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Staging

No staging system currently exists for primary neoplasms of the petrous apex.

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