Abarca Olivas, J (1); Lloret Garcia, J (1,2)
(1)Department of Neurosurgery Hospital General Universitario Alicante.
(2)Department of Neuroanatomy Facultad de Medicina Universidad Miguel Hernández.
Position. Supine, Ipsilateral shoulder roll if head turned >30º. Elevate thorax 10-15º reduces venous distension. Flex knees. Mayfield 3 pin head-holder: applied between true AP and true lateral (so that it is horizontal when head is rotated to the necessary position). Neck extended 15º. Head rotated from 30 to 60º depending the exposure required. For posterior exposure 30º, for middle exposure 45º and for anterior exposure 60º.
Curviline incisión is performed from zygomatic arch 1cm in front of tragus (to avoid frontal branch of facial nerve and frontal branch of superficial temporal artery) and finishing near or beyond midline. The incision should be posterior if the complete Sylvian fissure must be exposed. If only the anterior part of the fissure is opened more anterior incision is necessary.
Before dissecting the temporal muscle, some important ladnmarks should be taken into account: the frontal branch of facial nerve (yellow line), the zygomatic arch and the superior temporal line (discontinuous line).
Interfascial dissection described by Yasargil (1987) is shown. The thin fat layer of the superficial temporal fascia is dissected and anteriorly reflected in order to protect the frontal branch of facial nerve.
The pericranium above the superior temporal line is reflected anteriorly. Sometimes this tissue is used as an autologous dural patch. The discontinuous line shows the place where the temporal muscle is incised to keep a band attached to the bone flap for muscular reconstruction.
Temporal muscle is anterior and inferiorly reflected in order to expose the pterional area. To avoid bleeding this action should be started from its inferior portion where the muscle is not very attached to the bone. Note the muscular band kept for reconstruction close to the inferior edge of the superior temporal line. If a wide exposure of the inferior part of the temporal lobe is needed, the removal of the zygomatic arch may be helpful.
There are numerous ways to perform the craniotomy . Usually two burr holes are sufficient. We recommend A and B to cross easily the sphenoid wing . The C burr hole is recommended in older patients where dura mater is usually attached to the bone. The B hole is called “keyhole” and is the most important one. It is located at the intersection of the zygomatic bone, the superior temporal line and the supraorbital edge. The drill must be correctly oriented posterior and inferiorly to avoid entering into orbit.
The surgeon may be orientated about brain structures following skull references. The Sylvian fissure is placed at the level of pterion. So the inferior frontal gyrus is located between pterion and superior temporal line ( See Step 9 and correlate two pictures).
In this specimen three burr holes are employed. We usually find difficult to cross the greater sphenoidal wing even with A and B. Most surgeons keep a small piece of bone in this point and fracture it during bone flap elevation. If the sphenoid wing is too prominent, this must be rongeured. The size of the craniotomy depends on the aim of surgery. If only a Sylvian fissure exposure is needed the frontal extension of the craniotomy is reduced.
The bone flap has been removed and dura mater has been opened as a flap pediculated towards the greater sphenoidal wing previously roungered to improve parasellar visualization. Sylvian fissure, Inferior frontal gyrus, Superior temporal gyrus and Middle temporal gyrus are exposed. Three pars of parasylvian inferior frontal gyrus must be distinguished: pars orbitalis (pOr) in relation to the orbital roof; pars triangularis (pT) the widest area of sylvian fissure (good place for start opening of sylvian fissure); pars opercularis (pOp) where Broca’s Area is located.
Surgical 3d example:
In this case left pterional craniotomy is performed.