Complications in the Management of Skull Base Meningioma

Keywords: skull base, meningioma, complications, adverse events, transcranial approach, transnasal endoscopic approach, CSF leak, skull base repair

Deopujari CE, Vikram S. Karmarkar

20.1 Overview

Mastering the art of avoidance of both intraoperative and postoperative problems is a key factor in operative excellence and optimization of outcome.— Michael L. J. Apuzzo¹.

All disease conditions and their management carry the inherent possibility of complications. Complications may be termed as adverse effects or undesired consequences of a disease, either in the diagnosis or its treatment. There have been differing views of what constitutes a complication after surgery and numerous attempts have been made to classify these events into medical or surgical, minor or major, or to grade them according to severity. ¹ This is useful to assess outcomes as well as compare the techniques or treatment methods. A recent addition to this has been the detailed grading of neurosurgical complications by Ibanez L et al. ²

Meningiomas have always held a special place in the hearts and minds of neurosurgeons. Although the first successful surgical excision of an olfactory groove meningioma is credited to Durante F in 1885, ³ it was in the era of Cushing and others, that many of our current concepts have crystallized. Harvey Cushing, in his Cavendish lecture of 1922, stated, “There is today, nothing in the whole realm of this surgery, more gratifying than the successful removal of meningioma with subsequent functional recovery, especially should a correct pathological diagnosis have been previously made. The difficulties are admittedly great, sometimes insurmountable and though the disappointments still are many, another generation of neurological surgeons will unquestionably see them largely overcome”. ⁴

With modern imaging, a correct pathological diagnosis for the meningioma (a term coined by Cushing) has been possible in majority of cases. Several generations of neurological surgeons have tried to surmount the challenges with technical advances in hemostasis, drilling techniques for access and microscope or endoscopic visualization, resulting in remarkable improvements in morbidity and mortality. Although, the majority of complications related to the surgery and postoperative period have considerably reduced, newer techniques of access to various locations have posed new challenges. This chapter aims to describe and analyze the location and approach related complications in skull base meningioma surgery, along with possible measures of avoidance and treatment.

The surgical goal is complete elimination of the tumor along with involved dura and bone followed by monitoring for residual or recurrent disease, and then tackling this with repeat surgery or adjunctive treatment. To this end, several classifications have been proposed and validated. The Simpsons grading ⁵ is the most common grading scheme for extent of resection and predicting of recurrence, whereas the Levine-Sekhar classification and its variants have been validated for prediction of resectability of skull base meningiomas. ⁶ Most neurosurgeons have their own philosophy for treatment of this lesion, from the very aggressive to the more cautionary. ⁷ Meningiomas at the base of the skull are particularly challenging for preservation of the nerves and vessels running along the base, as also for the reconstruction of the skull base.

20.2 Preoperative Factors for Prediction of Complications

20.2.1 Clinicoradiological Factors

Skull base meningiomas can arise from a wide variety of locations from the olfactory bulb anteriorly to the foramen magnum inferiorly. These lesions come to notice if they cause focal deficits, convulsions, or lobar dysfunction (usually frontal). Unfortunately, in many parts of the world, some of the early symptoms like headache, retro-orbital pain are considered nonspecific, and hence may be ignored by the patients. Therefore, these lesions may attain a large size and multicompartmental involvement may be present by the time they seek medical care.

Larger lesions cause raised intracranial pressure and present with generalized headaches, visual disturbance, and papilledema. Localized headache, seen with convexity meningioma is usually missing in skull base lesions. However, sellar/parasellar tumors can cause an ill localized headache and retro-orbital pain. This is thought to be caused by dural stretch. Sometimes, lesions at the skull base may be found incidentally with no apparent clinical features, during a scan for other reasons, viz., head injury or magnetic resonance (MR) evaluation of the cervical spine. The challenge here is to decide if treatment is needed, what approach and strategies to follow for minimizing complications and optimizing outcomes. Nakamura et al ⁸ studied the natural history of 47 incidental (majority—skull base) meningiomas and concluded that the rate of growth of these tumors was slow. Most could be followed with serial imaging. Younger patients and higher signal intensity on T2 images were predictive factors for faster growth rate while the presence of calcium and lower signal on T2 suggested lower rates of growth. Others have advocated an observation only policy if the lesion is asymptomatic, reserving the surgical option for patients younger than 65 years of age who have increased in size or become symptomatic on follow-up. Patients older than 65 years, with symptomatic tumors smaller than 3 cm, tend to be treated with stereotactic radiosurgery; symptomatic patients with a larger tumors are usually treated with surgery and adjuvant radiotherapy if necessary. ⁹ We have usually followed the policy of observation in asymptomatic patients over 65 years in difficult locations.

Radiologic assessment is an integral part of the management and many imaging factors need to be assessed to predict possible complications. Perilesional edema is a harbinger of a higher-grade lesion and possible seizures in the perioperative period. The so called “lions mane” which is bifrontal edema due to an anterior skull base meningioma has been shown to extend the postoperative stay (▶ Fig. 20.1). It is also associated with more frontal lobar dysfunction in the perioperative period. ¹⁰ The so-called “brain cuff” which is brain edema or a rim of gliotic brain around an anterior skull base meningioma is considered by some a more challenging lesion to manage, especially through the transnasal route. ^{11,​ 12} More recently, a meta-analysis by Schwartz et al ¹³ have not found this to be uniformly applicable.

Neural canal involvement must be looked for especially at the optic canal in clinoidal, tuberculum, sellar, and parasellar lesions. Other foramina which can be affected include the foramen rotundum, foramen ovale, internal acoustic meatus, jugular foramen, and hypoglossal canal.

Tumors arising in the cavernous sinus or extending into the cavernous sinus need careful evaluation as vascular and nerve compromise can be expected with aggressive excision. Tumors medial to the carotid are amenable for transnasal endoscopic excision while tumors lateral to the carotid require more extensive skull base transcranial approaches.

CT reveals the degree of hyperostosis, in cases of skull base meningiomas, which needs to be drilled to achieve a more complete excision and decompression. It also reveals the degree of bone erosion, especially of the petrous bone in cases of petroclival or sphenopetroclival meningiomas. This is essential to prevent damage to the petrous internal carotid artery (ICA) and greater superficial petrosal nerve during tumor resection.

An important component of noninvasive vascular imaging is the CT angiography (CTA) or the MR angiography (MRA). Encasement or displacement of the major arteries and their branches can then be anticipated. This impacts the operative strategy. Imaging should also be carefully analyzed to identify involvement of the adventitia of the ICA to prevent catastrophic bleeding. Identification of a dominant and hypoplastic vertebral artery helps in deciding the safer surgical corridor in cases of anterior foramen magnum meningiomas (▶ Fig. 20.2).

To summarize, the following radiological parameters should be carefully evaluated for avoiding complications during surgery of a skull base meningioma, namely, presence of arterial encasement or invasion, invasion of cavernous sinus, involvement of cranial nerves, orbital invasion, dural or brain invasion, and involvement of the other dural venous sinuses. These factors are not only helpful in selecting a suitable corridor but also to predict and prevent intra- and postoperative complications.

Digital subtraction angiography (DSA) and preoperative embolization of skull base meningiomas has been a strategy in many neurosurgical units. In our opinion today, DSA should be done only if there is a possibility and need for preoperative embolization or carotid sacrifice is being planned. Though a common practice in our department till 2000 was to embolize these tumors; currently, we do not practice the same and our strategy is to begin by detaching the tumor from the skull base, reducing the major blood supply. The supply from the external carotid artery (ECA) is usually the most amenable for embolization. Variations, “dangerous anastomoses” between ECA and ICA are a potential hazard during embolization and need to be recognized and avoided to prevent cranial nerve deficits. ¹⁴

20.2.2 Multidisciplinary Approach

It is important to emphasize the need of a team approach to tackle these difficult tumors. Ideally, these cases should be performed at a center which has sufficient experience dealing with these tumors. Close collaboration with otorhinolaryngologists, radiologists, interventional radiologists/endovascular surgeons, oncologists, stereotactic radiosurgeons, craniofacial surgeons etc. may be necessary in cases of large and invasive tumors.

20.2.3 Surgeon Factors

Many skull base meningiomas can be treated with equal efficacy using endoscopic skull base approaches instead of the transcranial route. In these cases, surgeon’s preference and experience also play a key role in selection of a surgical approach. Availability of intraoperative navigation, micro-Doppler to identify vascular structures, intraoperative electrophysiological monitoring has helped us achieve more radical resections with safety. We have no access to intraoperative MRI and/or CT which may be useful to assess the degree of resection.

20.2.4 Patient Factors

Significant medical comorbidities, prior radiotherapy, prior surgery pose significant challenges in achieving a safe and complete resection of a skull base meningioma.

20.3 Perioperative, Operative Complications and Prevention

20.3.1 Anesthesia Considerations

Anticipation and avoidance of anesthesia related complications needs vigilance and prompt actions. Preoperative assessment and optimization of cardiorespiratory, renal, hepatic, and hematologic parameters is vital. Proper positioning and padding of the pressure points is necessary to prevent position related compression neuropathies. In the supine position, slight flexion of the knees prevents hyperextension and locking of the knee joint. Padding under the elbow prevents damage to the ulnar nerve and padding below the ankle/Achilles tendon is necessary to prevent pressure injury. The head is usually fixed in a skull clamp or supported by soft gel pillow if pin fixation is not used. In the prone position, adequate padding is needed for the chest, pelvis, patellae, and the forefoot. The skull rests on a gel pillow if not immobilized in a skull clamp. If a gel pillow/horseshoe head holder is used, extreme vigilance is required to ensure there is no pressure on the globes of the eyes. This is to ensure a potentially disastrous pressure induced visual compromise. ¹⁵ Lateral positions need care for the dependent part of the body, especially the arm, brachial plexus, and peroneal nerves of the bent, dependent lower limb. For the sitting position, excessive flexion of the neck must be avoided. Occasionally, this can lead to quadriparesis postoperatively. ¹⁶ Other possible complications seen with the sitting position include hypotension, air embolism, pneumocephalus, and increased incidence of subdural hemorrhages.

Induction of anesthesia needs to be smooth as some these patients have compensated intracranial pressure. There is a role for a lumbar drain, especially for extended endoscopic skull base procedures. In this case, care must be taken to prevent excess drainage of cerebrospinal fluid (CSF) prior to the excision. This may cause brain shifts and herniation syndromes in larger tumors. Similar vigilance should be exercised with external ventricular drainage.

End tidal carbon dioxide monitoring (EtCO₂), oxygenation (SpO₂), and blood pressure maintenance are vital for optimal brain perfusion. Strategies where intraoperative neurophysiological monitoring is used include maintaining the level of anesthesia on inhalational agents, intravenous anesthetics, and to avoid paralyzing agents.

20.3.2 Operative Complications

 Brain Swelling

For the transcranial approaches, preoperatively, steroids may be started if significant brain edema is noted on the MRI. In these cases, a bolus of 20% mannitol with or without furosemide can be administered during craniotomy to avoid brain swelling. After completion of the bone work, on opening the dura, if brain swelling persists then the following strategy checklist should be used:

1. 
   

   Position of patient: Extreme twisting or awkward position of head and neck can hamper venous return and may lead to a full brain. It is best to position the head around 30° above the heart level and to avoid extreme twisting of the neck.

   
   
2. 
   

   Depth of anesthesia and ventilation: The patient must be adequately under anesthesia. This aids brain relaxation avoiding brain swelling. Various monitoring devices and scales like the bispectral index quantify the depth of anesthesia. Maintenance of carbon dioxide tension also contributes to a lax brain.

   
   
3. 
   

   Bone removal: Sometimes, additional osteotomies may need to be performed in cases of persistent brain swelling to improve tumor visualization. Some of these manoeuvres include performing at orbitozygomatic osteotomy, orbital bar osteotomies etc. in cases of anterior skull base meningiomas.

   
   
4. 
   

   CSF release: Early release of CSF from a cistern or the Sylvian fissure can reduce the brain swelling. Alternatively, release of CSF from the lumbar drain or the external ventricular drain has a similar effect.

   
   
5. 
   

   Prevention of venous injury: It is important to plan and perform the craniotomy meticulously to prevent damage to the dural venous sinuses and major draining veins. The transverse and sigmoid sinuses are at risk while performing a retrosigmoid approach for a posterior petrous meningioma, while the vein of Labbe and the Sylvian veins, sphenoparietal sinus may be at risk while performing a subtemporal approach and fronto-orbitozygomatic osteotomy, respectively.

   
   
6. 
   

   Brain retraction: Once the brain is lax after the manoeuvres, a brain retractor may be used primarily to provide a clear surgical trajectory. ¹⁷

In case all the above fail, it may be sometimes necessary to resect some part of the brain to create a clear surgical corridor, viz., temporal or frontal polectomy or resection of lateral one-third of cerebellum, which is seldom necessary these days because of excellent anesthetic drugs and monitoring. Some consider it prudent to abandon the procedure and to re-explore after an interval.

During the endonasal approaches, the skull base meningioma is usually directly accessed at the end of skull base drilling and dural opening and then gradually debulked. Hence, brain swelling is usually not a problem. Larger tumors are usually not amenable to transnasal excision.

 Hemorrhage

The best way to tackle intraoperative hemorrhage is to anticipate the possibility of hemorrhage. Adequate arrangements for blood transfusion should be made based on the radiological features. Preoperative embolization should be considered in selected cases. Sequential coagulation and disconnection of the lesion usually devascularize the skull base meningioma almost completely, however, pial parasitization of small branches may be seen occasionally. This coupled with internal tumor debulking is the most commonly used technique for excision. Careful dissection from the pial surface is essential to prevent damage to the normal vasculature of the brain. Maintaining the pial-arachnoid plane is the key to prevent “en passant” vessels as well as perforators.

 Damage to Neural and Vascular Structures

Meningiomas at the skull base have close contact with one or more cranial nerves, the basal surface of the brain or the brainstem and intracranial blood vessels. Arachnoid is the best protective cover for a cranial nerve and the neuraxis including the brainstem. Careful dissection should be done to dissect the tumor from the cranial nerves and the brainstem, whilst preserving the pia arachnoid layers. Special attention must be paid to the nerves running through the posterior fossa, in cases of posterior fossa skull base meningiomas. Occasionally, some part of these tumors is closely adherent to the adventitia of major blood vessels. Here, it may be prudent to leave some tumor behind to prevent neural/vascular damage (▶ Fig. 20.3). Intraoperative monitoring is extremely useful in these cases to identify the cranial nerves and prevent iatrogenic injury.

Related posts:

Introduction Petroclival Meningiomas Foramen Magnum Meningioma Middle Fossa Floor Meningiomas Cerebellopontine Angle Meningiomas Cavernous Sinus Meningiomas

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