Indications
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Lesions in the cerebellopontine angle and petroclival region can be surgically challenging to resect because of surrounding vascular and eloquent neural structures (i.e., brainstem) that have zero tolerance for retraction. Numerous surgical approaches, such as translabyrinthine, transcochlear, and presigmoid approaches, are part of the surgeon’s armamentarium. Retrosigmoid craniotomy allows for easy and rapid access to the cerebellopontine angle.
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The extended version of the traditional retrosigmoid craniotomy is characterized by bony skeletonization of the sigmoid and transverse sinuses with an optional additional mastoidectomy. This modified version permits access to areas that are difficult to access with the classic approach—ventral to the brainstem and near the tentorium. This technique can often serve as a safe alternative to more radical cranial base approaches.
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This approach can be employed for extraaxial lesions in the cerebellopontine angle and intraaxial lesions arising along the petrosal surface of the cerebellum, cerebellar peduncles, or brainstem.
Contraindications
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Patients must have patent contralateral transverse and sigmoid sinuses before manipulation of the sinuses ipsilateral to the approach.
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This approach is relatively contraindicated in older patients with poor-quality dura mater; in these patients, a craniectomy as opposed to a craniotomy should be performed.
Planning and positioning
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Preoperative planning includes assessment of the patient’s cardiopulmonary status, evaluation of comorbidities, and basic laboratory tests, including a basic metabolic panel, complete blood count, coagulation profile, and type and screen. Baseline chest x-ray and electrocardiogram are also useful.
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In addition to standard magnetic resonance imaging (MRI) for intraoperative guidance, magnetic resonance venography is also obtained to ensure that the venous sinuses contralateral to the approach are patent before manipulation of the transverse and sigmoid sinuses ipsilaterally.
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Within 60 minutes of skin incision, perioperative antibiotics are administered.
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Brain relaxation can be achieved by administering mannitol, dexamethasone, and mild hyperventilation. For moderate-to-large lesions, a lumbar subarachnoid drain is also placed for intraoperative drainage; this drain is removed at case completion before extubation.
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After anesthesia induction, a multichannel central line and precordial Doppler is placed for early intraoperative detection and management of air embolism.
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Surgical navigation can be used as an adjunct depending on availability and complexity of the case. Surgical navigation can aid in the precise location of the transverse and sigmoid sinuses and in the placement of the burr holes before making the craniotomy flap.
Figure 6-1:
The patient is placed supine on the operating table with the ipsilateral shoulder elevated as needed to facilitate head rotation toward the contralateral side. The skull clamp is fixated with paired posterior pins at the equator in the occipital bone and single anterior pin at the equator in the contralateral frontal bone superior to the orbit. The head is positioned by first elevating the head above the heart in the “sniffing” position. Second, the head is rotated up to 60 degrees to the contralateral side depending on the intended operation. Third, the neck is extended so that the vertex is angled down 10 to 30 degrees, allowing for self-retraction of the frontal lobe off the anterior cranial fossa floor. When the head is ideally positioned, the malar eminence of the zygomatic bone should be the highest point in the operative field.Related posts:
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