Complications in Surgery of the Lateral Skull Base
The lateral skull base has a complex anatomy and contains the pyramidal temporal bone with its sensory end organs and neurovascular structures as well as important adjacent intracranial and extracranial structures. Surgery to this anatomical region inevitably, therefore, carries a risk of complications, the outcome of which may significantly affect quality of life and may be devastating for the patient.
The combination of a prolonged and complex neuroanesthesia and extended tumor resection by a multi-disciplinary team including otologists, neurosurgeons, head and neck, vascular and plastic surgeons, as well as the necessity for a complex reconstruction exponentially increases the risk of potential complications.1 Patients considered for skull base surgery, therefore, generally exhibit a unique set of factors predisposing them to complications of which their anatomical site and their histopathologic heterogeneity are of paramount importance.
Skull base lesions are frequently beyond a single surgeon′s area of expertise.
A multidisciplinary team approach, therefore, is essential to plan a resection involving major vascular, central nervous system, cranial nerve, and pharyngeal components of tumor management. The patient′s age, general health and in particular their cardiovascular and pulmonary status necessitates careful consideration because the surgery is major and protracted. Fluid balance with volume replacement as necessary is critical in both perioperative and postoperative care. The risk of neurologic deficit and in particular aspiration either perioperatively or intraoperatively must be considered and managed appropriately. The ability and willingness to cope with skull base tumor management is also influenced by the patient′s psychosocial status. Previous therapy may also affect the surgical resection and reconstruction plan. The majority of patients have failed previous therapy and the consequences of surgery following radiation therapy significantly increases the potential for complications. The concept of the “learning curve” in the early years of consultant appointment is no longer acceptable and yet, for most complex operations, learning is a career-long process. Subspecialization offers part of the solution to this problem by concentrating expertise, but there remains the question of how to introduce new team members without adversely affecting patient outcome.2 “Dove-tailing” with an inexperienced surgeon working alongside a senior surgeon for several years as well as proleptic surgical appointments can be very successful in minimizing the effects of the surgical learning curve.
This chapter outlines the differential diagnosis and therapeutic options of patients with complications from lateral skull base surgery. The management of complications of the lateral skull base is a highly complex part of this surgery, which is generally performed by otolaryngologists and neurosurgeons as part of a multidisciplinary team. The subspecialty encompasses the preoperative evaluation, discussion of the most suitable approach and the postoperative management. Evaluation of patients with diseases affecting the lateral skull base can be complex both from an investigative viewpoint and in terms of surgical management. A wide variety of pathologic conditions may occur in lateral skull base surgery. Numerous surgical approaches and procedures have been described for dealing with them. There are many very important neurovascular structures in this anatomical region and surgery will inevitably result in complications. There is not necessarily one single right solution to the management of any particular problem in lateral skull base surgery. Multiple factors have to be considered in dealing with complications resulting from surgery. We need to audit our own results and outcomes and compare them with published data. Only then will patients be able to give informed consent to our surgical intervention.
The diagnosis and management of minor and major complications during lateral skull base surgery and in the postoperative period are highlighted and discussed.
Careful and detailed discussion and counseling preoperatively is important to provide the patient and family members with sufficient information to make a balanced judgment on optimal management and to give informed consent to the surgical procedure. This understanding may subsequently help them to cope with the sequelae and complications should they occur.
The patient′s expectations of the treatment must be realistic and the risk of complications must be defined and quantified. Alternative treatment options like watch, wait and rescan strategies and radiation therapies such as stereotactic radiotherapy either by single-dose gamma-knife radiosurgery, cyberknife or by multiple-fraction linear accelerator should be discussed with an oncologist in a multidisciplinary team setting.
Associated Sequelae and Complications of Skull Base Surgery
The fine distinction between a sequela and a complication must be discussed with the patient and family preoperatively. There are many consequences of surgery that are unavoidable and are inevitable sequelae of the procedure and not a complication of it.1 These, however, may be viewed as complications retrospectively by the patient or the family if they are not adequately informed and consented. Patient satisfaction with the care received is increased if there is an ongoing preoperative and postoperative discussion between the surgical team and the patient and relatives explaining the reason for the clinical course and its likely final surgical outcome. Some expected sequelae of lateral skull base surgery may be incisional hair loss, altered facial sensation, possible change in facial contour, temporary facial or permanent segmental or complete facial paralysis, eustachian tube dysfunction, conductive or sensorineural hearing loss, vertigo, tinnitus, variable trismus and malocclusion, atrophy of temporal fossa, diplopia, hoarseness and swallowing difficulty.1
In view of the anatomical localization of most tumors involving the skull base, the preoperative physical examination must be complemented by detailed high-resolution contrast-enhanced computed tomography with bone window sequences and gadolinium-enhanced magnetic resonance imaging.3 Patients with tumors involving the petrous carotid artery should undergo preoperative angiography with cross-flow studies. This involves test balloon occlusion of the ipsilateral carotid system. First, a standard angiogram is completed and then the test balloon occlusion is performed with a soft balloon catheter. The occlusion is performed in the internal carotid artery with the patient awake. Subsequently with the assistance of an anesthetist to monitor the vital signs the blood pressure is pharmacologically lowered until the patient develops neurologic symptoms and signs.
Approximately 10% of patients tested fail to tolerate the balloon occlusion test. There is potential for clotting proximal to the balloon and subsequent embolization distal to the deflated balloon at the conclusion of the balloon occlusion test. Arterial spasm and hypoperfusion, particularly in the medial cerebral distribution, may occur. In elderly or previously irradiated patients, inflation of the balloon in a manner that produces an elongation of the balloon within the artery can fracture the intima or even rupture the arterial wall.
Positioning of the Patient on the Operating Table
Surgery of the lateral skull base can be performed with the patient in a lateral supine position or in a sitting position depending on the surgical team′s preference.4 Some neurosurgeons advocate the “park bench” position.
Lateral Supine Position
The lateral supine position is suitable for the majority of lateral skull base procedures and has been used predominantly in vestibular schwannoma surgery, where in many centres it has become the position of choice. This position is also preferable in patients with an open foramen ovale.
The patient is placed in a supine position with a cushion supporting and elevating the ipsilateral shoulder. The head may be placed in a three-point headring with a “mayo clamp” and the head is rotated through 45 degrees to the opposite side (this may vary depending on the size and anatomical localization of the tumor). The head is then clamped in the optimal position under the direction of the surgeon. It is imperative to protect the patient from falling off the table with two wide straps, one around the thorax and the other over the superior iliac crests because it might be necessary to tilt the table during surgery.4
The risk of skin or nerve pressure injury during long surgical procedures can be avoided by meticulous positioning of the patient and the careful use of gel cushions and pneumatic mattresses as well as using cotton wool pads between the patient′s arms and the armrests.
Sitting Position (“Beach Chair Position”)
Complex cerebellopontine angle (CPA) tumor procedures can be performed with the patient in a sitting position if the suboccipital or retrosigmoidal approach is used.4,5 This approach offers perfect conditions for microsurgical manipulation because all fluids drain out of the operative field. The surgeon has both hands free for surgical maneuvers because the necessity for suction of cerebrospinal fluid is significantly reduced. The sitting position, however, embraces the risk of air embolism. This can be reduced significantly by placing a special cushion under the patient′s legs to lift the legs to the level of the heart and the teeth to the same level as the frontal region. If the venous sinus is opened during surgery the assistant should irrigate the operative field copiously resulting in aspiration of fluid through the defect and not air. If air is detected by transesophageal echocardiography, it can be aspirated by the anesthetist using a central-line catheter. If a definite sinus laceration cannot be detected, speedy compression of the jugular vein by the anesthetist may be helpful and the head should be immediately lowered below heart level and the legs raised. It is also necessary to cover the surgical field with soaked cottonoid patties or strips of lintine. The risk of air embolism is the reason why the sitting position is rarely used in the United States, the United Kingdom or the Netherlands. Neurosurgeons in these countries prefer the lateral position.
Potential Anesthetic Complications
General anesthesia requires careful and meticulous preparation. All available monitoring techniques should be used, including arterial lines, central venous pressure monitoring, pulse oximetry, electroencephalography, temperature probe, and urinary catheterization with output measurement and frequent blood gas measurement, intraoperative hematologic evaluation including clotting studies if there is a risk of diffuse intravascular coaguloapathy. If necessary a brain pressure probe can be used.
The complications of neuroanesthesia include those due to the anesthetic agents themselves, such as hypotension and hypoxia, unsatisfactory control of the PaCO2 and subsequent brain swelling.
Pneumothorax is a potentially dangerous condition that may arise unexpectedly during anesthesia or after insertion of a subclavian central venous catheter ( Fig. 6.1 ). The diagnosis is one of exclusion, as initial changes in vital signs (cardiorespiratory decompensation and difficulties with ventilation) may be nonspecific. The other causes of such changes are more common than pneumothorax. Additionally, local signs may be difficult to elicit, especially without full access to the chest. The diagnosis may be made by chest aspiration in suspected cases and correct insertion of a chest drain is essential for the further safe conduct of anesthesia and surgery.6
A fluid volume overload needs to be avoided in lateral skull base surgery. The use of intraoperative mannitol to reduce intracranial pressure must be carefully monitored. Abnormalities of fluid and electrolyte balance may adversely affect organ function and surgical outcome. Perioperative fluid therapy has a direct bearing on outcome, and prescriptions should be tailored to the needs of the patient. The goal of fluid therapy in the elective surgical setting is to maintain an effective circulatory volume while avoiding interstitial fluid overload whenever possible.7
Medical complications that occur after skull base procedures may be pulmonary, including atelectasis, aspiration pneumonia and respiratory failure, or cardiovascular, such as myocardial infarction and hypertension. Air emboli are more likely to occur in the sitting position. A degree of postsurgical pneumocephalus occurs in all patients with craniotomies,8 and is usually resorbed within 2 or 3 days.
Several factors can increase a patient′s risk of deep vein thrombosis, including advanced age (the highest risk factor) and prolonged surgery, which is likely in lateral skull base procedures. Deep vein thrombosis is the formation of a thrombus in a deep vein, most commonly in the legs. Besides acquired risk factors such as old age, obesity and smoking, there are other factors like high fibrinogen levels and inherited risk factors, e.g., antithrombin deficiency and Protein C deficiency/Protein S deficiency. An abnormal D-dimer level at the end of treatment might signal the need for continued treatment among patients with a first unprovoked proximal deep vein thrombosis. Pulmonary embolism is a blockage of the main artery of the lung or one of its branches by a substance that has travelled from elsewhere in the body through the bloodstream ( Fig. 6.2 ).
Renal complications comprise urinary tract infection and renal failure. Hematologic problems like bleeding diathesis, transfusion reaction or transfusion-transmitted disease may occur.