Учебники / Middle Ear Surgery
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166 32 Vestibular Neurectomy – Transtemporal Approach
Fig. 32.3 |
Fig. 32.4 |
followed by sectioning of the inferior nerve including the ganglion. Sharp dissection is preferable to prevent injury of vessels serving the cochlea nerve. Small vessels on the vestibular nerve are cauterized with bipolar forceps (Fig. 32.4).
The defect is closed with fascia and a muscle graft stabilized by fibrin glue. The bone removed by the craniotomy is replaced after suture of the dura incision. The covering tissue layers are sutured.
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33 Retrosigmoidal Approach
Martin Scholz
Introduction
The vestibulocochlear nerve is composed of three parts: the inferior and superior vestibular nerves and the cochlear nerve. The two vestibular nerves fuse to become one nerve before they exit from the internal acoustic meatus. The vestibular nerve and cochlear nerve join to form the eight cranial nerves closer to the brain stem. Indications for the suboccipital retrosigmoidal approach to the vestibular nerve are extremely rare. Only limited clinical experience has been gained with microvascular decompression of the vestibulocochlear nerve for the treatment of tinnitus or vertigo. The procedure of cutting the vestibular nerve as a treatment for therapy-resistant vertigo should be used only in a small group of selected patients who have failed to respond to all other therapeutic modalities.
Surgical Procedure
Positioning
The operation can be carried out with the patient in a sitting or lateral position at the surgeon’s discretion.
Sitting Position
In our opinion surgery performed for the treatment of complex cerebellopontine angle tumours should be carried out with the patient in a sitting position if the suboccipital retrosigmoidal approach is used. This approach offers perfect conditions for microsurgical manipulations since all fluid (e.g. blood) rinses out of the operative field. The surgeon has both hands free for operative manipulations; suction of collected fluid is not necessary. Despite this advantage, however, the sitting position poses the risk of air embolism.
The risk of air embolism can be reduced to nearly zero by optimizing several conditions. We recommend placing a special cushion under the patient’s legs in order to lift the legs to the level of the heart and the teeth to the same level as the frontal region. The patient is now no longer sitting but is in more of an embryonic or astronaut position (Fig. 33.1). Following this procedure the pressure in the sigmoid sinus is not less than zero and air embolism is extremely rare.
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If sinus opening occurs the assistant should rinse the operative field extensively so that fluid and not air will be aspirated by the sinus. If air is detected in the precordial Doppler, it can be aspirated by the anaesthesiologist using the central catheter. If sinus laceration cannot be detected, quick compression of the jugular vein by the anaesthesiologist is sometimes helpful. If depression of the cardiopulmonary circulation results, the head should be positioned lower and the feet higher using the table steering remote control. With this constellation it is necessary to cover the operative field with wet Cottonoid paddies.
With the patient in a sitting position two different devices can be used for the surgeon’s armrest. The first device is a special board, connected to the operating table, which can be angled and fixed in different ways to meet the surgeon’s individual requirements.
It is important to simulate the surgical procedure and arm position after positioning the patient but before sterile draping in order to create a comfortable situation for the surgeon. The patient’s head position can vary according to his or her height. If the patient is sitting too low, it is not possible to collect cerebrospinal fluid. If the patient is sitting very high, in contrast, we have to operate free handed, which is very uncomfortable. The proper adjustment of the patient on the operating table allows the surgeon to proceed in a calm and totally satisfying manner. The other possibility for an armrest is the so-called “chicken ladder” (Fig. 33.2). This device is also adjustable; however, it is too narrow and causes pain in the forearm if used for long operations.
During positioning the head of the patient is turned slightly towards the side of the tumour and the chin is angled downwards (cave: compression of the jugular vein).
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, which is described in the following.
Lateral Supine Position
In our opinion this position is suitable for microsurgical vestibular neurectomy and is in fact the position of choice for this procedure. The patient selected for this intervention has to be placed in a supine position with a cushion supporting his/her shoulder. The arm should be stretched slightly to the opposite lower corner of the operating table to bring the shoulder out of the surgeon’s reach (Fig. 33.3). The head is then turned to the opposite side; the chin should be brought upwards. The Mayfield clamp should be adjusted so that it does not hinder later microsurgical manipulations. Using the remote control for the operating table, the surgeon can also turn the patient to the opposite side if necessary. It is important to protect the patient from falling off the table with an additional holding device. If right-sided vestibular nerve neurectomy is planned, the surgeon and assistant surgeon are standing side by
33 Retrosigmoidal Approach 169
Fig. 33.1
Surgeon II |
Nurse |
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Surgeon I
Fig. 33.2 |
Fig. 33.3 |
170 33 Retrosigmoidal Approach
side. For the left-sided procedure the surgeon and assistant surgeon are standing face to face.
Skin Incision
After local shaving of the hair behind the pinna and disinfection of the surgical field, a curved skin incision is made; this incision crosses a line running from the asterion to the protuberantia (Fig. 33.4). The asterion can be palpated behind the outer ear and is a nice bony landmark for the angle between the sigmoid and transverse sinuses. After undermining the skin edges inside the subcutaneous tissue for a distance of up to 2 – 3 cm on each side, the surgeon fastens several sterile compresses with metal clamps. It has to be stated clearly that exact haemostasis is extremely important at all stages of the intervention as a prerequisite for successful microsurgical manipulation.
The nuchal muscles (m. semispinalis, m. splenius and in part the m. sternocleidomastoideus) are split with the monopolar knife. The surgeon must be aware that, when the procedure is performed with the patient in a sitting position, an air embolism can also be produced by opened muscle veins.
Preparation of Subcutaneous Tissue and Nuchal Muscles
Normally the surgeon should be able to reach the suboccipital bone below the external occipital protuberance in the upper region of the incision. The muscle can then be pushed away easily using a rasp. Sometimes it is helpful during this step to use the monopolar knife to cut away the bony attachment of the muscles. If we insert a wound retractor into the operative field to stretch the muscles, the surgical procedure is much easier.
Care should be taken not to injure the occipital artery and to preserve the major occipital nerve (cave: development of neuroma). If we reach the pars horizontalis and lower portions of the muscles, damage to the vertebral artery is possible, especially if the surgeon steps too lateral and low. It is advisable to carry out these preparation steps in the time-honoured way with scissors, tweezers and bipolar coagulation if necessary and to refrain from using the monopolar at this point. During this part of the operation one big wound retractor in the upper part of the incision and one wound retractor below will be a good solution to open up the operative field (Fig. 33.5). If we have detected several bony landmarks, e.g. the origin of the mastoid, suboccipital bony structures with dimensions of approximately 4 × 4 cm, and the pars horizontalis, we can focus on the next part of the intervention – the trephination.
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Fig. 33.4
Fig. 33.5
Trephination
Either osteoclastic or osteoplastic bone resection can be performed. The surgeon has to bear in mind here that the dura is much more adherent in the cerebellar region than in the supratentorial areas. This poses the risk of sinus damage with possible air embolism. For safety reasons we normally use the big 15mm trepanation head creating four to five bore holes nearby; the resulting bone dust is saved. Following the intracranial intervention and dura closure this bony material can be introduced into the bony defect to ensure good cosmetic results later. The size of the trephination has to be 3×4 cm at minimum. The complete sigmoid sinus and parts of the transverse sinus are now exposed with the drill. Attention should be paid to the emissary veins, which naturally lead to the sigmoid sinus. These openings can be closed easily with Tabotamp and a Cottonoid paddy or bone wax if there is a small bony layer lying above. Aggressive coagulation should be avoided in the sinus region. Parts of the pars horizontalis are taken with the Luer in a medial direction for the later opening of the cisterna magna and gain of cerebrospinal fluid.
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Fine Work with the Drill
To reach the sigmoid sinus the surgeon has to drill away parts of the air-filled mastoid in nearly all cases; the drilling is accompanied by continuous rinsing with NaCl 0.9 % by the assistant. If the surgeon does not approach the complete sinus at this point, the subsequent dural incision will be too far toward medially, and pressure to the cerebellum with possible infarction will result (Fig. 33.6). During the closure procedure to be performed later the opened mastoid should be covered with some pieces of muscle mixed with fibrin glue.
Withdrawal of Cerebrospinal Fluid
This is a very important step during the operation. The aim of this procedure is to relax the cerebellum by opening the cisterna magna. Under microscopic magnification the dura should be opened in a triangular shape in the region of the pars horizontalis (Fig. 33.6). The surgeon enters the intracranial space between the dura and the cerebellum carefully using a suction tube and a forceps with a small Cottonoid paddy. If the cisterna magna is reached medially, it can be opened easily with the tips of the bipolar forceps. If a large amount of cerebrospinal fluid is withdrawn from the cistern, the intracranial space will relax and further intracranial microsurgical manipulation can be performed under better conditions.
Opening of the Dura
The dura has to be opened near the sinus via a curved incision that connects with the previous dural opening. The dura is fixed with sutures and the cerebellum is covered with Cottonoid paddies for protection. A spatula can be introduced into the operative field later to hold the cerebellum medially. It should be pointed out clearly that the use of a spatula is not necessary if the cerebellum is relaxed and all steps have been carried out correctly up to this point.
Intracranial Part
The intracranial procedure that now follows is complex. Monitoring of the facialis with a stimulation forceps serves as the gold standard here. Intracranial orientation should be undertaken via the visualization of the trigeminal nerve, petrosal vein and other structures. To achieve further relaxation of the cerebellum, the trigeminal cistern can be opened with the bipolar forceps. The cistern of the vestibulocochlear and facial nerve is then detected and has to be opened. From a topographic point of view the vestibular nerve with its superior and inferior part is located facing the surgeon coming from the described approach (Fig. 33.7). The nerve can be separated from the facial nerve with a small nerve hook. The separated nerve should be stimulated as well as the facial nerve in order to detect the facial nerve with both neurophysiological and anatomical methods.
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Fig. 33.7
Fig. 33.6
In addition to monitoring the potentials received from the microelectrodes in the mimicry muscles, the anaesthesiologist should watch the face of the patient under the sterile drapes carefully for mimicry movements. It is logical that it is much easier to observe the patient’s face when the patient is in the sitting position. If the vestibular nerve is detected correctly, it can be coagulated with low energy and cut with microscissors. The ends of the cut nerve can be coagulated again to shrink the nerve and prevent later regrowth. During all of these surgical steps, the application of energy to the facial nerve should be avoided. It must be stressed here that vestibular neurectomy is a destructive procedure with the inherent possible complication of damage to the facial and cochlear nerves if the anatomical situation is not entirely clear.
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Closing Procedure
Closing of the dura in the posterior fossa is not easy and should be carried out with pedantic care. It is sometimes necessary to close small gaps in the dura with pieces of galea. If the dura is sutured in a watertight manner under microscopic magnification, layers of Tabotamp with fibrin glue are laid on the dura followed by the bone dust which is used to fill in the bony defect. It is important not to forget to close the mastoid with muscle. Should CSF fistula occur, otogenic rhinoliquorrhoea is possible if cerebrospinal fluid enters the opened mastoid. In this case a postoperative lumbar drain should be inserted and left in place for 5 – 10 days. The muscle layers should be sutured carefully; subcutaneous sutures and skin sutures follow closure of the muscle layers.
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34 Otological Instruments
Jürgen Lautermann, Holger Sudhoff, Henning Hildmann
Not all instruments are used for every procedure. A set of instruments should be small enough to avoid any loss of time searching for the required instrument. This is not only time efficient but also cost efficient and makes assisting the surgeon easier.
There are different sets for different otosurgical procedures. We recommend small sets for paracentesis and positioning of ventilation tubes; sets for mastoid surgery, surgery of chronic ear inflammations and their sequelae; sets for stapes surgery; and special instruments for skull base surgery.
Instruments for Middle Ear Surgery (Fig. 34.1)
Instruments for Stapes Surgery (Fig. 34.2)
Special Instruments
Footplate microdrill (Skeeter drill) for stapes surgery
House-Urban midfossa dura retractor (Fisch modification) for acoustic neuroma surgery
Facial nerve monitor for acoustic neuroma surgery, surgery for middle ear malformations
Operating Room Arrangement
For middle ear surgery the surgeon sits on the side of the ear which is to be operated on and the scrub nurse sits at the top of the table. The instruments are placed between the surgeon and the assisting nurse. The microscope, if not fixed to the ceiling, is placed opposite the surgeon. The anaesthesiologist is positioned either opposite the surgeon or on the same side. The patient is in a supine position, the head slightly tilted to the opposite side.
For the transtemporal approach (middle fossa approach) in skull base surgery, the surgeon is seated at the head of the patient with the scrub nurse at the side of the table.