Skull Base, Petrous Apex, Tumors Treatment & Management
- Author: Michael J Fucci, MD; Chief Editor: Arlen D Meyers, MD, MBA more...
Petrous apicitis (as seen in the CT scan images below) is an inflammatory process often secondary to suppurative otitis media. Medical therapy is aimed at eliminating bacterial infection and promoting drainage with aggressive antibiotic therapy. Streptococcus pneumoniae, Haemophilus influenzae, and Staphylococcus aureus are the primary pathogens responsible for petrositis. Steroids may help decrease inflammation, pain, and swelling. Early surgical intervention is critical because of the severe complications secondary to chronic otitis media and petrous apicitis.
Skull base osteomyelitis is primarily a medical disease requiring long-term antimicrobial therapy directed against Pseudomonas aeruginosa. Severe otitis externa with granulation tissue in an immunosuppressed patient is the most common clinical setting. Often, the pain is described as deep and boring, with this symptom seeming out of proportion to physical findings. Aminoglycosides, coupled with an antipseudomonal penicillin derivative, are the antibiotics of choice. Quinolone antibiotics offer enteral therapy with encouraging results. Gallium-67 scanning is used to monitor the course of the disease. Technitium-99 scanning is more specific in the diagnosis, but findings remain positive after the course of the disease so they cannot be used to monitor therapy.
With the exception of petrous apicitis and skull base osteomyelitis, all lesions of the petrous apex are best treated surgically. Preoperative histologic diagnosis or strong clinical suspicion is critical to making the proper surgical plan. The availability of an experienced and skilled neuroradiologist is critical in making a confident and accurate preoperative assessment. Ask to have the films read elsewhere if the preoperative imaging studies are inconclusive or vague. The diversity of apex lesions does not permit characterization of the surgical approach. The specific surgical techniques are discussed in Intraoperative details.
Careful preoperative evaluation is critical in minimizing intraoperative and postoperative complications. Neurologic examination allows a thorough understanding of preoperative deficits. Preoperative imaging studies define the exact size and location of the lesion. Angiography determines the vascular supply of the particular lesion and helps to narrow the differential diagnosis to assist in choosing the best treatment approach while avoiding complications. Autologous blood or donor-directed blood availability is addressed preoperatively. Often, central venous monitoring and arterial monitoring are helpful in the intraoperative and postoperative period.
One of the most significant decisions regarding surgery is the choice of approach. Factors influencing the approach choice include the location and size of lesion, suspected histopathology, facial nerve function, hearing level, vestibular function, trigeminal function, and surgical experience.
The main approaches currently used to access the petrous apex are systematically described below.
This approach was initially developed to drain fluid in petrous apicitis. It includes the supralabyrinthine approach, the subarcuate approach, and the retrofacial approach. These approaches permit limited exposure of the apex. They preserve hearing and carry little risk to the facial nerve but do not allow sufficient exposure for tumor resection.
William House popularized the middle fossa approach as a method of excising acoustic neuromas while preserving hearing. Others described this approach to access the petrous apex. Intracanalicular tumors smaller than 1.5 cm and serviceable hearing are approached through the middle fossa in some centers. The criterion for middle fossa approach in acoustic surgery has expanded to include larger tumors with some extension into the cerebellopontine angle. Facial neuromas, facial hemangiomas, trigeminal neuromas, cholesterol granulomas, congenital and acquired cholesteatomas, and some petroclival meningiomas can also be approached through the middle fossa subtemporal craniotomy.
The transcochlear approach described by House is essentially an anterior extension of the translabyrinthine approach. After a translabyrinthine approach is performed, the greater superficial petrosal nerve is cut anteriorly to the geniculate ganglion, and the nerve is taken out of its bony canal from the proximal internal auditory canal to the stylomastoid foramen. The facial nerve is reflected posteriorly, and the bony cochlea is removed with a drill. The anterior extent of the bony dissection is the petrous portion of the carotid artery. The procedure provides excellent exposure but leaves the patient with anacusis in the operated ear. Often, return of facial function is incomplete because of the extensive nerve manipulation. Meningiomas and cholesteatomas, especially when the hearing is already compromised, are often resected by this approach.
The infracochlear approach is used primarily to drain petrous apex cholesterol granulomas. This approach is generally transcanal in the triangular space bordered anteriorly by the carotid artery, posteriorly by the jugular vein/bulb, and superiorly by the basal turn of the cochlea. Exposure is limited with this approach, and its usefulness is limited to draining cystic lesions of the apex.
Transethmoid-transsphenoid (open and endoscopic)
In 1977, Montgomery described the open approach through an incision near the medial canthus. This approach is best for cystic lesions in contact with the posterior wall of the sphenoid sinus. The lesions are drained into the nose, and a silicone stent is often used to keep the tract open. The intranasal transsphenoidal endoscopic approach was first described by Fucci in 1994. This method opens the sphenoid sinus and then opens the posterior wall of sphenoid sinus into the cyst. A stent is placed to keep the pathway open.
Fisch has used the infratemporal fossa type B for petrous apex exposure and the type C to obtain more medial access, even into the nasopharynx. These approaches need to be mentioned as viable options.
Various combinations of these approaches are useful and frequently used to access the apex. The size and nature of the mass and the potential morbidity with the acceptable exposure influence the approach.
Newer available imaging techniques such as CT image-guided surgery and MRI-guided surgery afford the surgeon a real-time evaluation of the location and the progress of the dissection. This can allow the surgeon to immediately determine the exact location of the carotid artery, internal auditory canal, cochlea, and other pertinent structures in relationship to the probe. Image-guided surgery is extremely helpful in these difficult cases in which cranial nerves and vital blood vessels traverse the surgical field.
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Petrous apicitis: Petrous apicitis is most common in well-pneumatized temporal bones. These lesions are often drained successfully through the transmastoid approach. In 1985, Chole described the surgical anatomy of the petrous apex. The supralabyrinthine, retrofacial, and subarcuate approaches usually allow sufficient exposure to drain the purulent material from the apex.
Skull base osteomyelitis
- Skull base osteomyelitis (ie, malignant otitis externa) is a severe osteogenic infection usually observed in elderly patients with diabetes mellitus or patients who are immunocompromised. The condition was first described by Chandler in 1968. Skull base osteomyelitis starts with severe otitis externa (swimmer's ear) with granulation tissue and purulent material in the external auditory canal. It is refractory to local treatment and is characterized by a severe, deep, and boring pain in the affected ear. Symptoms usually are out of proportion to the physical findings. CT scan and MRI findings are usually nondiagnostic.
- Sometimes, the CT reveals bone destruction. Bone scans are the most helpful imaging modalities in diagnosing these disorders. In advanced cases, cranial neuropathies occur from extensive inflammation of the skull base.
- P aeruginosa is the most common pathogen accounting for this disease. Bone scan using technitium-99 shows uptake in the region of the skull base. Findings on gallium scans are nonspecifically positive but are useful in monitoring patient response to treatment because bone scans remain positive after the clinical course of the disease. Treatment traditionally consisted of aminoglycosides and synthetic penicillin for 4-6 weeks. The use of oral quinolones has shown significant efficacy and is rapidly becoming the standard of care. The avoidance of aminoglycoside antibiotics reduces the incidence of ototoxicity and nephrotoxicity and the complications of long-term intravenous antibiotic delivery in treated patients. Some advocate use of adjunctive hyperbaric oxygen therapy. Surgical therapy is designed to remove abscess formation and necrotic bone in refractory cases.
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- Cholesterol granuloma is the most common pathologic lesion of the petrous apex. These lesions are hyperintense on both T1- and T2-weighted MRI, as shown below. The imaging characteristics are shown in Table 2.
Cholesterol cyst. A coronal T1-weighted image of the temporal bone shows high-intensity signal in the left petrous apex.
- The terms cholesterol cyst or giant cholesterol cyst are used to describe the same or similar lesions. One study, however, suggests that cholesterol granulomas and giant cholesterol cysts are distinctly different entities. The term cholesterol granuloma describes a giant cell foreign body reaction in conjunction with fibrosis, vascular proliferation, hemosiderin-laden macrophages, and round cells.
- These lesions occur elsewhere in the temporal bone, frequently secondary to surgery, chronic otitis media (with or without cholesteatoma), and chronic eustachian tube dysfunction. These granulomas develop from poor ventilation with a relative vacuum, resorption of air, mucosal hemorrhage, and hemoglobin breakdown leading to cholesterol formation.
- Cholesterol granulomas have no cyst wall and do not require complete surgical excision. Treatment is drainage with establishment of a permanent ventilation system. Often, silicone tubing is used to stent the drainage system and prevent stenosis. The transcanal infracochlear approach described by Giddings provides hearing preservation with direct gravity-dependent access to the apex. The transsphenoidal approach, either external or transnasal endoscopic, provides direct access to the lesions while preserving hearing. The situation is ideal if the lesion abuts the posterior wall of the sphenoid sinus. The intrapetrous carotid artery is immediately posterior to the sphenoid sinus, and great care is required to avoid injury when using a transsphenoidal approach. A plastic stent is placed to connect the cyst to the nasal cavity.
- A systematic literature review by Eytan et al indicated that cholesterol granulomas of the petrous apex can be successfully treated with endoscopic endonasal management. Examining data from 53 patients treated in this way, the investigators found that, over a mean follow-up period of 20 months, cholesterol granuloma symptoms improved or resolved in 98.6% of cases. Complications (most commonly epistaxis) reportedly occurred in 13.2% of patients. Although restenosis was found in 9 out of 45 patients on follow-up endoscopic examination, only four patients had symptomatic cyst recurrence.
- Some authors advocate the middle fossa subtemporal extradural approach. The cyst is opened and plastic is placed from the cyst to the eustachian tubes or epitympanum. The drainage is not gravity dependent, and stents have eroded into the dura, causing cerebrospinal fluid otorrhea and meningitis. The transcochlear approach is useful for large lesions in patients with hearing impairment. It is a technically challenging approach that requires relocating the facial nerve posteriorly, a procedure that not infrequently causes some residual facial dysfunction. The transcochlear approach is an aggressive approach that provides excellent exposure.
- A study by Sweeney et al suggested that cholesterol granulomas of the petrous apex often remain stable and can therefore in many cases be managed via primary observation rather than surgery. The study included 90 petrous apex cholesterol granulomas, none of which during a mean 46-month follow-up spontaneously ruptured or caused carotid injury. The investigators stated that surgery normally should not be performed unless these granulomas are—through mass effect or erosion of the otic capsule or other critical structures—causing or likely to cause neurologic dysfunction.
- Cholesterol granuloma is the most common pathologic lesion of the petrous apex. These lesions are hyperintense on both T1- and T2-weighted MRI, as shown below. The imaging characteristics are shown in Table 2.
- Congenital cholesteatomas are nonmalignant epidermoid cysts derived from ectoderm trapped in the temporal bone. These expansile lesions are sterile unless they erode into the middle ear or external auditory canal. Acquired cholesteatomas occur from eustachian tube dysfunction causing retraction of the tympanic membrane or from epithelial migration through a tympanic membrane perforation. MRI shows low-intensity signal on T1-weighted images and high-intensity signal on T2-weighted studies.
- Cholesteatomas are nonenhancing after administration of gadolinium. They are usually distinguished from cholesterol cysts by differences in the T1-weighted images, although cholesteatomas have variable intensity on T1-weighted imaging. CT scanning shows an expansile lesion in the apex that does not enhance with contrast administration. Acquired cholesteatomas usually show middle ear and mastoid disease with abnormal findings on otoscopic examination.
- In both congenital and acquired cholesteatomas, the goals of surgery are complete removal of squamous epithelium, preservation or restoration of hearing, and maintenance of normal anatomy. Exteriorization of the cholesteatoma is a valuable technique that allows the cholesteatoma cavity to be cleaned through the ear canal.
- The choice of surgical approach for petrous apex cholesteatomas requires the consideration of several important factors, including cranial nerve function, hearing status, carotid artery involvement, intracranial extension, size of lesion, bacterial contamination, spinal fluid otorrhea, and surgical experience. Congenital cholesteatomas in the apex have no contact with middle ear, mastoid, eustachian tube, or sphenoid sinus. Therefore, they are sterile, and the choice of approach depends on size and surrounding structures. Acquired cholesteatomas are contaminated with bacteria, and great care is required to avoid seeding the subarachnoid space and brain with pathogens. The presence of cerebrospinal fluid otorrhea or rhinorrhea requires repair of the defect, often by packing the defect with fat or muscle to obliterate the cavity. Recurrent disease is more difficult to detect with obliterative techniques, however.
- Exteriorization is performed when complete excision cannot be safely executed without sacrificing vital structures such as the cochlea, facial nerve, or carotid artery. Cleaning the cavity or cholesteatoma bed is necessary to prevent accumulation of cholesteatoma with subsequent infection and bony erosion, possibly leading to intracranial complication.
- Imaging studies are necessary because of the high rate of recurrent or residual disease. As in chronic ear surgery, some recommend a second stage operation at 6-12 months after the initial surgery to look for residual or recurrent cholesteatoma. Others recommend annual CT scanning or MRI to detect residual or recurrent disease. Exteriorized lesions are examined through the ear canal, looking for cholesteatoma, otorrhea, or an occluded drainage site.
- Mucoceles are cystic structures most commonly found in the paranasal sinuses. These expansile lesions manifest secondary to obstruction of mucous glands. Bone destruction occurs through pressure necrosis. They are differentiated from cholesterol granulomas by CT scanning, where the fluid within the cyst is isodense with cerebrospinal fluid. The contralateral apex usually is well pneumatized. MRI shows a hypointense signal on T1-weighted images, and cholesterol granuloma is hyperintense on both T1- and T2-weighted images. It is differentiated from cholesteatoma by mucoceles enhancing on T1-weighted images with gadolinium.
- If the mucocele is not expanding and symptoms are minimal, treatment is unnecessary. Consider surgery only with an expanding lesion or with significant symptoms. The goal of surgery is establishment of a permanent drainage route, often using a stent to prevent occlusion of the drainage pathway.
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- Meningiomas arise from the arachnoid villi of the meninges. They are the most common benign tumor of the intracranial vault. Cerebellopontine angle meningiomas arise from the posterior surface of the petrous pyramid. Petroclival meningiomas arise from the clivus or the most medial aspect of the petrous apex. The tumors are often diagnosed by imaging studies prompted by cranial neuropathies and headache. Some meningiomas are locally invasive, while others exhibit little or no growth.
- CT scanning shows a broad-based dural attachment, focal calcium deposits, hyperdensity to brain, and moderate homogenous contrast enhancement. Hyperostosis of the nearby calvaria can occur. MRI shows broad-based dural attachment, heterogeneous signal pattern, moderately intense homogenous enhancement, and surrounding brain edema. On T1-weighted images, 60% of the lesions are isointense, 30% are hypointense, and 10% are hyperintense. On T2-weighted images, 50% of the lesions are isointense, 40% are hyperintense, and 10% are hypointense. All intensities are in comparison to adjacent brain. Meningiomas frequently contain calcium deposits that cause signal voids. The most specific feature of a meningioma on MRI is an enhancing dural connection (ie, tail sign). These tumors have a rich vascular supply from dural vessels.
- Numerous approaches are used to resect meningiomas, with the specific choice dependent on tumor size, tumor location, hearing status, facial nerve status, and surgeon experience. Recurrence rates for meningiomas are high, and complete resection is the goal in growing tumors. The effects of stereotactic radiation on meningiomas are unclear. Some suggest that growth is arrested and that stereotactic radiation should be used as the primary treatment. Others suggest that the role of radiation is only postoperative, to prevent or delay recurrence.
- Schwannomas originate from the Schwann cells lining the nerve. When found in the petrous apex, they usually originate from cranial nerves V, VII, and VIII. In rare cases, large schwannomas from the lower cranial nerves grow into the apex. An MRI image of a trigeminal schwannoma is depicted in the image below.
- Cranial neuropathies and headaches are the most common presenting symptoms of schwannoma. CT scanning shows a smooth expansile lesion with postcontrast enhancement. MRI shows low-intensity signal on T1-weighted images and high-intensity signal on T2-weighted images. These lesions enhance with gadolinium administration.
- Chordomas occur rarely and arise from notochord cells, primarily in the sphenoid and clivus. Tumors originating within the apex are rare, and spread is usually from the clivus. Patients with chordomas present with progressive cranial neuropathies and headache. They occasionally manifest with an invasive mass in the nasopharynx. Chondroid variants of chordoma account for 15% of all chordomas.
- CT scanning shows an erosive and irregular mass that enhances with contrast administration. MRI reveals low intensity on T1-weighted images and increased signal on T2-weighted images. Contrast administration shows heterogeneous enhancement. Chondroid chordomas are more homogenous on MRI.
- Surgery with postoperative radiation is the treatment plan of choice. Chordomas are difficult to completely excise and are only moderately radiosensitive. Average survival with aggressive treatment is only 4 years. Chondroid chordomas are less aggressive, with an average survival time of 15 years.
- Chondrosarcomas account for only 0.15% of all intracranial neoplasms. Hearing loss, pulsatile tinnitus, vertigo/unsteadiness, VI palsy, and headaches are the presenting symptoms. CT scanning shows irregular bone destruction with contrast enhancement. MRI shows enhancement with gadolinium (greater than observed with chordomas). Complete surgical excision with postoperative radiation therapy is the treatment plan of choice. Chondrosarcomas are histologically graded, and survival depends on grade as well as symptoms, origin of lesion, and efficacy of surgical extirpation. An MRI image of a chondrosarcoma is depicted in the image below.
- Advanced cases of nasopharyngeal carcinoma invade the clivus and infiltrate the petrous apex. Patients present with unilateral otitis media, headache, cranial nerve palsies, and neck mass. A careful inspection of the nasopharynx, often requiring directed biopsies, is indicated. Treatment involves radiation therapy with chemotherapy. CT scan images of nasopharyngeal carcinoma are seen in the images below.
Metastasis: Breast carcinoma and prostate carcinoma metastasize to the temporal bone, especially to the petrous apex and the clivus. Kidney, lung, gastric, and thyroid carcinoma metastasize to the apex less commonly. When these lesions are discovered in the temporal bone, studies suggest the lesion has already metastasized elsewhere. CT scan and MRI characteristics are specific to the primary tumor and dependent on whether the tumor causes an osteogenic or osteoblastic reaction. The prognosis in patients with distant metastasis remains poor.
Direct extension from temporal bone
- Squamous cell carcinomas and basal cell carcinomas (as seen in the MRI image below) of the temporal bone can directly invade the petrous apex. These tumors are usually easily detectable because the lesion is visible on the skin or in the ear canal.
- The tumor seen in the above image obstructed flow through the sigmoid sinus. MRI venogram seen in the image below shows sigmoid sinus obstruction.
Intrapetrous carotid aneurysm
Aneurysms of the intrapetrous carotid artery are extremely rare, with fewer than 50 cases reported in the literature. Presenting symptoms are often hearing loss and neuropathies of cranial nerves IV, V, and VII. CT scanning shows a smooth expansile lesion of the carotid canal. Intravenous contrast shows enhancement in continuity with the carotid artery. MRI depends on the state of blood flow within the aneurysm. An acute thrombosis shows low signal intensity on T1-weighted images and high signal intensity on T2-weighted images.
Immediate postoperative examination is imperative. This allows assessment of neurologic status to determine postoperative deficits and to establish a baseline to monitor postoperative progression. Neurologic status, including facial nerve status, hearing condition, and trigeminal function, is critical in determining the success of the surgery and potential postoperative complications. A postoperative intracranial hematoma is suspected when the patient is extubated and has a change in mental status. Electrolyte and hematocrit surveillance along with radiographic imaging are standard in the postoperative care in these complex cases. Most patients who have undergone craniotomies receive a CT scan with no contrast on postoperative day one to evaluate the cranial vault for bleeding, brain compression, and hydrocephalus.
Care and thorough follow-up is imperative. In petrous apicitis, CT scanning is important to determine if suppuration recurred or is residual. Examination and imaging studies are necessary to determine if the drainage tract is open or closed. In skull base osteomyelitis, gallium scanning is often used to follow the course of the disease because technetium scan findings remain positive after treatment is no longer necessary. Cholesteatomas, both congenital and acquired, are monitored by clinical examination and imaging studies. The apex is difficult or impossible to visualize through the ear canal, and cholesteatomatous recurrences are common. Consequently, interval imaging studies are recommended. Cholesterol cysts are most commonly treated with drainage procedures, and the drainage tract can close. Efforts are made to keep the drainage tract open.
Reaccumulation of fluid and expansion of the cyst is possible, and imaging studies are necessary in the determination. Mucoceles behave similarly to cholesterol cysts with closure of the drainage tract with possible reaccumulation of mucus and expansion of the mucocele. Neoplastic lesions have a high risk of recurrence. Baseline postoperative imaging studies are necessary to establish residual disease and postoperative changes. These radiographs are then compared with new studies when looking for changes suspicious for residual or recurrent growing tumor. Of course, serial examinations are performed, with attention to the neurologic portion of the examination most closely related to structures at or near the apex.
Hearing loss (cranial nerve VIII)
Hearing loss is a common complication of surgery for lesions of the apex. Direct trauma to the cochlea or cochlear nerve accounts for profound hearing losses. Effusion, ossicular dislocation, ossicular drill trauma, encephaloceles, scar tissue, and other problems account for most conductive losses and partial hearing losses.
Facial paralysis (cranial nerve VII)
Facial paralysis is an unfortunate complication of petrous apex surgery. Facial nerve monitoring is considered the standard of care and provides useful intraoperative information. Immediately repair known surgical transection of the nerve. Use of a graft depends on the tension of the repair. Immediate implementation of eye care, including drops, ointment, and nighttime taping or patching, is critical in preventing exposure keratitis. A moisture chamber is also helpful in preventing dryness. If paralysis is permanent, other eye care and facial reanimation techniques are used to improve function and appearance.
Cerebrospinal fluid leak
Spinal fluid leak occurs through the wound, directly into the nose through the sphenoid sinus, or through the eustachian tube into the nasopharynx. The most critical factor needed to prevent CSF leak is meticulous intraoperative wound closure that addresses all possible routes of CSF drainage. Techniques to decrease the incidence of CSF leak include careful wound closure; packing of the eustachian tube, middle ear, and mastoid defect; packing of the nasopharynx and sphenoid sinus; and intraoperative lumbar drain placement. CSF leak can lead to meningitis, and aggressive therapy is indicated. Occasionally, the middle ear space is obliterated, the epithelium of the tympanic membrane and external auditory canal is removed, and the ear canal is oversewn closed. This measure has little consequence unless hearing is sacrificed.
Clinical determination of a CSF leak is usually quite clear. Occasionally, laboratory studies including glucose and beta-2 transferrin are used to verify CSF presence. Slow intermittent leaks are sometimes verified by localization studies. These slow leaks sometimes stop with lumbar drainage and supportive care. If the leak persists, surgical management is warranted.
Infection of the meninges is an uncommon complication of apex surgery. Acquired cholesteatomas account for the most severe intracranial infections because of middle ear and mastoid contamination. Meningitis is often associated with CSF leak. Clinical suspicion of meningitis is high, and diagnosis is rarely delayed. Treatment with antimicrobial therapy is started after proper cultures are obtained.
Recurrent disease, whether infectious, inflammatory, or neoplastic, is a possible complication of petrous apex surgery. Careful history, thorough physical examination, and appropriate imaging studies are necessary to detect recurrences without undue delay.
Vertigo (cranial nerve VIII)
Damage to the labyrinth or the vestibular nerve usually causes a transient vertigo that resolves by central compensation. Incomplete labyrinthine insults and damage to the brain stem due to the pathologic condition or treatment can occasionally lead to severe intractable vertigo. Vestibular rehabilitation is the mainstay of therapy for fixed peripheral vestibular dysfunction. Only the most severe cases require an additional vestibuloablative procedure. Central vertigo requires long-term medical management.
Glossopharyngeal nerve and vagus nerve (cranial nerves IX and X)
Paralysis of these 2 nerves causes significant morbidity and occasional mortality. These nerves elevate the larynx and palate to protect the airway. They provide sensation to the base of tongue and supraglottic region to stimulate adduction of the vocal cords in order to prevent aspiration. Injuries to the glossopharyngeal and vagus nerves cause dysphagia, odynophagia, aspiration, decreased or ineffective cough, poor pharyngeal and esophageal motility, and inability to recognize food or secretions. Aspiration, pneumonia, and weight loss is common. Appropriate speech and swallowing therapy is critical, and additional surgical procedures, including thyroplasty, tracheostomy, feeding tube placement, gastrostomy, and others, are occasionally necessary to protect the airway, clear pneumonia, and provide nutrition.
Cerebral edema often occurs secondary to intraoperative retraction, interruption of venous drainage, and brain manipulation. It usually occurs several hours after surgery but can occur several days after surgery. Mental status change and a lateralizing or focal neurologic deficit are classic findings of cerebral edema. Some surgeons routinely obtain postoperative CT scans at certain intervals to screen for edema. Treatment is supportive and includes hyperventilation, mannitol, fluid restriction, and possibly corticosteroids.
Hematomas are potentially life-threatening complications that can cause pressure on the brain with subsequent change in mental status and respiratory depression. History, physical examination, imaging studies, and clinical suspicion permit early detection and prompt treatment. The hematoma must be evacuated and the cause of the bleed corrected. In intradural hematomas, the tumor itself or vessels that supplied the tumor are the culprits. In extradural hematomas, the middle meningeal artery is often the cause of bleeding. A small piece of surgical packing can be placed within the foramen spinosum to prevent hemorrhage. Dural edges are occasionally tacked to the bony margin of the craniotomy flap to eliminate dead space. Drains are sometimes used to prevent hematoma formation.
Fluid and metabolic disturbances
The pituitary-hypothalamic axis can be disturbed by surgery, especially if the operative site is near the pituitary gland itself, although any surgical manipulation or head trauma can cause difficulties. The syndrome of inappropriate antidiuretic hormone secretion (SIADH) and diabetes insipidus (DI) are the most common metabolic disorders from skull base surgery. Careful fluid management and occasional use of exogenous hormones is necessary to correct the electrolyte disorders. These abnormalities are usually transient with no long-term sequelae or treatment.
Postoperative seizures can occur after any intracranial procedure, especially if the temporal lobe is manipulated. Prompt control of seizure activity is necessary to prevent increased intracranial pressure and bleeding. Laboratory studies and imaging studies are performed to identify possible causes.
Stroke and embolism
Postoperative strokes are potentially devastating complications of petrous apex surgery. Patients requiring carotid sacrifice should undergo preoperative vascular studies including a balloon occlusion test. If the patient passes the balloon occlusion test, some recommend xenon-enhanced CT scanning because 10-15% of those who pass the balloon test develop ischemia. Only 2% of those passing both the balloon occlusion test and the xenon CT scanning develop ischemia. Thrombosis of the anterior inferior cerebellar artery in the posterior fossa may cause stroke, while cerebral edema, increased intracranial pressure, and hematoma can cause decreased blood flow and stroke. Venous occlusion can cause vascular compromise and subsequent stroke. Cases of dural sinus thrombosis causing cerebral edema are reported. Vascular spasm from intracranial manipulation causes vascular compromise and loss of function.
Future and Controversies
Continual improvements in surgical techniques, imaging studies, intraoperative monitoring, and improved antimicrobials should decrease the morbidity and mortality of petrous apex surgery. Neurootologists and neurosurgeons have specialized training in treatment of these unusual disorders, so the operators are more experienced. Centers for skull base surgery are developing where petrous apex lesions could be sent. This will possibly allow pooling of these rare tumors, so that the centers would have increased experience and presumably increased expertise.
Cochlear implants now provide hearing in previously deaf individuals with an intact cochlea and cochlear nerve. Auditory brainstem implants to provide hearing in deaf individuals with no cochlear nerve by directly stimulating the cochlear nuclei are in development. An increased understanding of the vestibular system is possible through basic science research and through the space program, where scientists can study the effects of weightlessness on the vestibular system.
In 1968, the Karolinska Institute in Stockholm first used gamma stereotactic radiation to treat brain tumors. In 1987, the University of Pittsburgh School of Medicine became the first center in the United States to use gamma stereotactic radiation from cobalt-60 sources to treat brain tumors. Several published studies now suggest that certain intracranial neoplasms are best treated with stereotactic radiation rather than microsurgery. Recent studies have suggested that gamma stereotactic radiation prevents growth of acoustic neuromas in more than 90% of cases. Some studies suggest that, in selected populations, more than 70% of untreated acoustic neuromas do not grow. Nevertheless, gamma stereotactic radiation offers promise in treating petrous apex neoplasms. Studies are underway to determine whether stereotactic radiation is more therapeutically effective and economical than microsurgery. This controversy continues.
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Obtain informed consent: Medicolegal issues often involve informed consent. The patient must be informed of all potential risks. A typewritten sheet that explains all risks and requires the patient's signature in addition to the standard hospital surgical consent form improves the patient's understanding of the potential consequences. Explain the risks with a family member present because the patient's understanding may be impaired due to emotional consequences.
Know and practice the standard of care: Standard of care issues are also significant medicolegal pitfalls. Use of a facial nerve monitor, an operating microscope, and the assistance of a neurosurgeon are often considered the standard of care. Close supervision of residents and fellows is critical to provide excellent education without sacrificing quality patient care.
Recognize limitations and obtain second opinions: Most attorneys scrutinize experience in treating these tumors. Do not risk performing these complicated operations without significant experience. Physicians are under ever-increasing pressure from insurance companies to perform operations that they would rather refer out because their more experienced colleague is not on the insurance panel. Avoid the pressure and refer out of network. Physicians rarely regret referring cases to more experienced colleagues. Realizing limitations and putting patient care at the pinnacle of the decision tree demonstrates excellent judgment.
Keep impeccable records: Carefully document all interactions with patients. Remember that if it was not recorded, it did not take place. Document follow-up recommendations, such as recommendation to return in 2 weeks if symptoms persist or patient refusal of tests such as MRI recommended for asymmetric hearing loss. Record missed appointments, cancellations, and phone conversations. Never, under any circumstances, alter a record. A case is indefensible if the record is altered.
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|Lesion||Bone Erosion||Eroded Margin||Contralateral Apex||Contrast Enhancement|
|Cholesterol granuloma||+||Smooth||Highly pneumatized||-|
|Cholesteatoma||+||Smooth||Often not pneumatized||-|
|Bone marrow asymmetry||-||-||Variable||-|
|*From Jackler RK and Parker D: The radiographic differential diagnosis of petrous apex lesions. AJO 1992;13:561-574|
|Lesion||T1 Images||T2 Images||T1-Gadolinium|
|Cholesterol granuloma||Hyper||Markedly hyper||No enhancement|
|Petrous apicitis||Hypo||Hyper||Rim enhancement|
|Bone marrow asymmetry||Hyper||Hypo||No enhancement|
|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|