Chapter 45 Drainage Procedures for Petrous Apex Lesions

Derald E. Brackmann, Neil A. Giddings, Eric P. Wilkinson

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With the help of cranial computed tomography (CT) and magnetic resonance imaging (MRI), petrous apex lesions can be correctly diagnosed preoperatively. Consequently, cystic lesions requiring drainage should be approached with procedures designed for drainage, not total en bloc removal. Although the transmastoid infralabyrinthine procedure has been the usual approach for these lesions, transcanal infracochlear drainage offers a more dependent drainage site. The eventual role of the various approaches for petrous apex drainage depends on the long-term follow-up of these patients.

Advances in radiologic imaging during the past 2 decades have made it possible to differentiate reliably lesions of the petrous apex preoperatively. The development of CT scanning was the first major step in imaging the temporal bone since the development of polytomography. CT scanning gives the surgeon the ability to visualize the size of the lesion and its relationship to vital structures, including the internal auditory canal (IAC), cochlea, vestibular labyrinth, carotid artery, and jugular bulb. It also helps characterize the border of the lesion as expansile or invasive, which may differentiate between benign lesions and malignant neoplasms. MRI of the temporal bone added the capability of characterizing the substance of the lesion, rather than its effect on bony interfaces, allowing the surgeon to distinguish between mucus, fat, cholesterol granuloma, cholesteatoma, and neoplasm. The combination of CT, with its superior bone imaging algorithms, and MRI, with its enhanced tissue imaging capabilities, allows the surgeon to differentiate accurately and reliably among benign cystic lesions, normal anatomic variants, and neoplastic lesions of the petrous apex.

Patients with petrous apex lesions present with various symptoms and physical findings. The most widely recognized finding is Gradenigo’s syndrome, consisting of retro-orbital pain, otorrhea, and ipsilateral sixth cranial nerve paresis. The signs and symptoms of noninflammatory or neoplastic lesions may be more subtle. Hearing loss and vestibular abnormalities are frequently associated with lesions of the petrous apex as they enlarge and compress the IAC. The facial nerve is relatively resistant to paresis from slowly expansile lesions, but may be involved early with neoplastic lesions of the petrous apex or non-neoplastic lesions compressing the IAC.

Pain may be present with benign or cystic lesions, but is more common in neoplastic lesions. Its distribution depends on the region involved. The mastoid cavity is innervated by CN IX and may radiate pain into the neck. The middle fossa and superior petrosal regions are innervated by CN V and may cause retro-orbital or facial pain. Lesions extending into the posterior fossa may cause pain along the routes of distribution of CN IX and X and the first three cervical nerves.¹ Although 80% of adult mastoid bones are aerated, only 30% of petrous bones have air cells extending to the apex, and 7% may have asymmetric pneumatization of the petrous apex.^2,³ The increasing use of MRI of the head and neck makes it imperative that the clinician can differentiate pathology from normal variant in the temporal bone. Table 45-1 summarizes common lesions of the petrous apex and their associated radiologic findings.

TABLE 45-1 Radiologic Appearance of Common Petrous Apex Lesions

Asymmetric pneumatization is clearly seen on CT scanning, but supplementary MRI may be needed to rule out pathologic lesions in a symptomatic ear. Normal bony architecture can be seen on CT scanning, with hyperintensity on MRI T1-weighted scans and hypointensity on T2-weighted scans because of the large fat content in marrow. Retained mucus in the air cells also appears with normal bony architecture on CT scan, but is hypointense on T1-weighted MR images and hyperintense on T2-weighted MR images. Cholesteatoma is usually associated with chronic otitis media, but may arise from congenital rest cells in the petrous apex. Because of its high water content, cholesteatoma is isointense with cerebrospinal fluid on CT, and is hypointense on T1-weighted MR images and hyperintense on T2-weighted MR images. Cholesterol granuloma is isointense with brain on CT scanning and appears as a classic image on MRI with hyperintensity on T1-weighted and T2-weighted scans.

Radiologic descriptions of other, less common lesions are also summarized in Table 45-1. Differentiating between chordoma, chondroma, and chondrosarcoma of the temporal bone remains difficult, even with the scanning techniques currently available. The area of origin and the age of the patient must be considered when the pathology of destructive lesions of the petrous apex is determined.⁴^–⁶

PATIENT SELECTION

Most surgical approaches to the petrous apex were developed in the preantibiotic era for drainage of petrous apex abscesses and cure of Gradenigo’s syndrome. With the arrival of modern antibiotics, infectious processes of the petrous apex have greatly declined in frequency, but these same approaches may be equally effective in draining cystic lesions of the petrous apex.

Air cell tracts extend above, below, and anterior to the otic capsule, allowing the potential of safe passage to the petrous apex. Approaches that follow superior air cell tracts include middle fossa,⁷ through the superior semicircular canal,⁸ the attic, and the root of the zygomatic arch.⁹ Approaches below the inner ear include the infralabyrinthine and the infracochlear.¹⁰^–¹³ Anterior approaches have been described by Ramadier,¹⁴ Eagleton,¹⁵ and Lempert,¹⁶ who used the triangle between the anterior border of the cochlea, the carotid artery, and the middle fossa dura. All these approaches are used for drainage of inflammatory disease processes that are not responsive to antibiotic therapy or simpler operations for chronic ear disease (Fig. 45-1).

FIGURE 45-1 Surgical approaches for drainage of petrous apex.

FIGURE 45-2. A, Exposure of cyst in infralabyrinthine cell tract. An island of bone protects retracted sigmoid sinus (Bill’s island). B, Silicone tube placed into interior of cavity drains into inferior mastoid cavity.

Infralabyrinthine, infracochlear, and transsphenoidal approaches are most commonly chosen for drainage of cystic lesions of the petrous apex in an ear with serviceable hearing. These lesions are frequently detected at an asymptomatic stage with current imaging techniques. Because the natural history of small benign cystic lesions is not well documented, surgical drainage should be reserved for patients with larger lesions or with symptoms including pain, visual changes, diplopia, hearing loss, vertigo, or facial nerve weakness. For patients without serviceable hearing, these lesions should be drained through a translabyrinthine approach. Because other vital structures may be affected by enlargement of the cyst, delaying surgery in symptomatic patients provides no advantage.

Cholesterol granuloma is the most common cystic lesion of the petrous apex, occurring 30 times less frequently than acoustic neuroma.¹⁷ It may develop in any aerated portion of the temporal bone, but most commonly occurs in the mastoid air cells distant to a lesion that prevents normal aeration. Cholesterol granuloma of the petrous apex probably develops when a pathologic process or trauma obstructs the air cell tracts to a well-pneumatized petrous apex.

The treatment for cholesterol granuloma of the temporal bone is drainage and re-establishment of adequate aeration to the involved area. The cyst wall is composed of a fibrous connective tissue. It is free of keratinizing squamous epithelium that characterizes cholesteatoma, and complete removal of the cyst is unnecessary.

Solid tumors of the temporal bone and cholesteatoma are removed when first identified, rather than after further symptoms develop because these symptoms frequently reveal further involvement of other vital structures. Drainage procedures are inadequate treatment for these lesions, and all reasonable efforts should be made to remove them entirely. Total removal may require the sacrifice of cranial nerves and major vascular structures.