Antegrade Subperiosteal Temporalis Muscle Elevation and Posterior Retraction Technique Avoiding Muscle Incision for Pterional Craniotomy: A Technical Note
Correspondence Address: Source of Support: None, Conflict of Interest: None DOI: 10.4103/0028-3886.355156
Source of Support: None, Conflict of Interest: None
Keywords: Facial nerve, pterional craniotomy, superior temporal line, temporalis fascia, temporalis muscle
Pterional craniotomy is a work horse of skull base surgery. The surgical strategy and nuances of the approach have been elaborately described. Subgaleal collection and periorbital edema in immediate postoperative period are common issues associated with this approach. Temporalis muscle atrophy and its related consequence is another issue in late postoperative period. A number of techniques of handling and elevating the temporalis muscle have been described. The technique of elevation of the muscle should be such that it is quick and easy and should provide optimal exposure. Majority of described techniques discuss a retrograde technique of temporalis muscle dissection, wherein the muscle is cut at the posterior limit of dissection and is elevated anteriorly [Figure 1]a., Facial nerve preservation is a key component and can be accomplished by either interfascial or subfascial dissection. This risk is minimized by elevating temporalis muscle together with the scalp but the muscle bulk reduces the exposure of the surgical field., Retrograde dissection technique is described in the literature which involves incising temporalis muscle then separating muscle subperiosteally and then elevating it from posterior to anterior. We report antegrade, subfascial, subperiosteal temporalis muscle dissection technique involving muscle elevation off temporal squama from anterior to posterior direction. We termed the technique as “antegrade” considering the existing terminology of the “retrograde” dissection technique. This technique preserves the vascularity of the muscle and minimizes muscle atrophy. The integrity of facial nerve branches is preserved by subfascial subperiosteal dissection over the zygomatic arch.
An antegrade subperiosteal elevation of the temporalis muscle was performed in 15 autopsy cases (30 temporalis muscles). Intactness of the subperiosteal membrane on the undersurface of the temporalis muscle was considered as the objective evidence of the neurovasculature preservation [Figure 1]b. This technique was implemented successfully in 50 patients undergoing pterional craniotomy for aneurysm surgery.
Incision over the scalp and fascial layers covering the temporalis muscle were taken using standard described techniques. The aim was to preserve the vascularity of the scalp and save the frontalis branch of the facial nerve. The scalp and its fascial layers are elevated anteriorly without entering into the subgaleal space. The zygomatic arch is exposed subperiosteally. The temporalis muscle is elevated from the temporalis fossa in a posterior direction in subperiosteal plane without taking any direct surgical incision in its bulk. The muscle is then rotated posteriorly. Posterior rotation of the temporalis muscle beyond the line of scalp incision is carried out either by “in-rolling” or “out rolling” techniques. Posterior “in-rolling” technique involves infolding of the muscle under the edge of the scalp incision. Subperiosteal dissection is carried out beneath and beyond the posterior margin of the scalp incision to provide space for in-rolling of the temporalis muscle (double breasting). The posteriorly rotated muscle is then secured by using the muscle hitch stitches and bringing the needle out from the scalp posterior to the incision [Figure 2]a, [Figure 2]b, [Figure 2]c, [Figure 2]d, [Figure 2]e. Another more frequently used method was “out rolling” technique in which temporalis muscle is rolled above the posterior margin of the scalp incision and is retracted posteriorly by hitch sutures [Figure 3]a and [Figure 3]b.
In all the surgical cases, temporalis fascia was incised along with scalp incision and was elevated by avoiding subgaleal space opening [Figure 2]a. The adhesion at the transition zone of temporalis fascia and pericranium along superior temporal line was separated with sharp dissection [Figure 2]b. Use of diathermy was avoided. Subgaleal and subfascial dissection of temporalis fascia was performed as described above [Figure 2]a and [Figure 2]b. Thin strip of muscle was left attached along superior temporal line and was used for reattaching temporalis muscle [Figure 4]a, [Figure 4]b, [Figure 4]c. Temporalis fascia and pericranium was approximated, and layered closure of scalp was performed [Figure 4]d, [Figure 4]e.
All patients were evaluated for immediate postoperative issues like subgaleal hematoma and periorbital edema. Late complication like temporalis muscle atrophy was evaluated by comparing it with the contralateral normal side of the same patient. On follow-up, all patients were enquired regarding chewing difficulty. Temporalis muscle bulk and strength was evaluated by palpating it during teeth clenching and objectively assessing by spatula test. The bulk was compared with the contralateral side temporalis muscle. Magnetic resonance imaging could have been another objective assessment of temporalis bulk but was not done due to cost consideration.
Antegrade subperiosteal elevation of the temporalis muscle was performed in 15 autopsy cases. Preservation of the subperiosteal membrane during muscle elevation was considered to be an objective evidence of intactness of its entire vascularity. Pterional craniotomy was performed with this technique in 50 cases for anterior circulation aneurysm. There was anterior communicating artery aneurysm in 27 cases, middle cerebral artery aneurysm in 11 cases, posterior communicating artery aneurysm in 6 cases, and supraclinoid internal carotid artery aneurysm in 6 cases. There were 21 females and 29 males with ages ranging from 26 to 81 years, and the mean age was 46 years. Out of 50 cases, the muscle elevation was done using the “in-rolling” technique in seven patients and with the “out-rolling” technique in 43 cases. Decision to use the “in-rolling” or “out rolling” technique was based on temporalis muscle thickness. Pterional exposure with this technique provided adequate exposure for aneurysmal surgery. Immediate postoperative subgaleal collection and periorbital edema was not encountered in any case. None of the cases had facial nerve injury or noticeable temporalis muscle-related complications with excellent cosmesis at 6 months of follow-up.
Temporalis muscle is embryologically related to the first branchial arch., Intraoperatively, this muscle is seen as one unit/structure, but it has three muscle bundles anteromedial, anterolateral, and middle lateral. Temporalis muscle lies between the temporalis fascia on the surface and the “subperiosteum” in the depth in approximation to the skull. Preserving these layers is important for its integrity, neural function, and vascularity. Loss of functional integrity and muscle atrophy leads to asymmetry and temporal hollowing. The three deep temporal nerves that are the branches of mandibular division of trigeminal nerve are located superficial to the subperiosteum indicating the need for subperiosteal dissection as well as avoiding diathermy for its preservation. Temporalis muscle has extensive anastomotic vascularity vertically and horizontally fed by MTA, anterior and posterior DTAs, and their connections.
DTAs and MTA form a plexus 1.8 cm below superior temporal line anastomosing with STA. The anterior DTA anastomoses with small branches of lacrimal artery, perforating the zygomatic bone and the greater wing of the sphenoid bone., The MMA has anastomosis with the DTAs in the temporal bone and with the STA through the temporal muscle, while the MTA anastomoses with the anterior and posterior DTAs., The vascularity of mobilized temporalis muscle is dependent on the DTAs and the STA, which emphasizes its need for preservation. Excessive retraction of the temporal muscle compromises blood flow through temporal arteries leading to ischemic changes starting within 15 min of retraction. Prolonged and excessive retraction leads to irreversible changes 6 to 8 h after ischemia.,
For basal exposure that requires excessive muscle retraction, zygomatic osteotomy is recommended to avoid tourniquet effect. Temporalis muscle can be damaged due to cutting, dissection, and retraction., Following the surgical procedure, reinsertion of the muscle at the original detachment site helps to retain muscle tension for optimal functioning and thereby preventing disuse atrophy.,
Insertion of muscle at the site of its attachment is done by screw fixation or directly attaching muscle to bone by drilling holes along the superior temporal line, which helps in maintaining adequate muscle tension, thereby preserving its functional integrity., Subfascial, subperiosteal dissection reflecting intact temporalis muscle inferoposteriorly avoids injury to the frontotemporal branch of the facial nerve especially the anterior and middle branch of the facial nerve. The orbicularis oculi and corrugator (anterior) and frontalis (middle) muscles are important for cosmesis. However, if incision is made up till the level of the tragus, the posterior branch of the tragus nerve, innervating the anterior and superior auricular muscles, is transected which does not cause any apparent deficit.
Retrograde dissection in subperiosteal plane has been described in the literature for preservation of the neuro-vasculature of the temporalis muscle [Figure 1]a. However, the antegrade dissection technique has not been reported in literature. Antegrade dissection proceeds from anterior to posterior. Temporalis muscle dissection in subperiosteal plane is continued posteriorly under direct vision till desired exposure is achieved. Dissection study carried out on 15 autopsy specimens assisted in assessing the feasibility of implementing this technique during pterional craniotomy. This provided evidence that antegrade dissection is safe if done maintaining the subperiosteal plane [Figure 1]b.
Adequate exposure for pterional craniotomy requires maneuvering of muscle bulk away from the surgical site. The technique of posterior retraction of the temporalis muscle is a better alternative for exposing the temporal bone in a pterional craniotomy. Although the technique of posterior retraction of temporalis muscle without incision is described in literature, however, the technique and its merits have not been detailed. We have advocated two methods of posterior retraction of temporalis muscle. First is the “in rolling” technique wherein temporalis muscle is rolled under itself on the posterior aspect of the temporal bone [Figure 2]c, [Figure 2]b, [Figure 2]e. Second method is the “out rolling” technique wherein temporalis muscle is rolled outward over scalp incision site [Figure 3]a and [Figure 3]b. The anterior part of temporalis muscle is securely positioned with multiple anchoring sutures during both “in rolling” and “out rolling” techniques.
The anchoring sutures are utilized in retracting temporalis muscle posteriorly. Stretching of the temporalis muscle with anteriorly placed hitch suture leads to thinning of muscle where it is bulkiest. Posterior retraction of the muscle bulk should avoid undue stretch. In the “out rolling” technique, temporalis muscle is rotated outwards with muscle traversing over the scalp incision site providing adequate pterional exposure [Figure 3]a and [Figure 3]b. In the “in-rolling” technique, hitch sutures are made to pass underneath the scalp far beyond the site of scalp incision [Figure 2]c, [Figure 2]d, [Figure 2]e. Hence, accommodation of muscle bulk in the “in rolling” technique necessitates subperiosteal dissection posterior and beyond the scalp incision site to create space for in rolled and retracted muscle. Choice of using the “in rolling” or “out rolling” technique is decided by the thickness (bulk) of temporalis muscle. The “In rolling” technique is usually preferred in cases with thick temporalis muscle; however, this technique can be used in all cases irrespective of the temporalis muscle thickness (bulk). For normal or thin temporalis muscle, the “out rolling” technique is recommended as it is simple and quick. The “In rolling” technique requires subperiosteal temporalis muscle elevation more than that required for the “out rolling” technique. This has potential of damaging neurovascular structures. Hence, we preferred to use the “out rolling” technique as far possible unless compelled by excessive muscle bulk to use the “in rolling” technique.
During closure, muscle can be sutured by drilling pin holes along superior temporal line. We preferred to incise the muscle and leave a thin strip of temporalis muscle attached along the superior temporal line for temporalis muscle reattachment and for securing bone flap. The anterior as well as the posterior end of the muscle left along superior temporal line is anchored at both the ends by sutures passing through this muscle, temporalis muscle and the temporalis fascia [Figure 4]a and [Figure 4]b. The temporalis muscle is reattached in its entire length along the superior temporal line [Figure 4]c.
The thickest component of the temporalis muscle lies underneath the zygomatic arch. Pterional craniotomy by the conventional technique involves temporalis muscle incision and retraction inferiorly obstructing the basal temporal bone exposure, particularly in the region of base of the sphenoid wing. Posterior retraction of the temporalis muscle as discussed creates muscle free space underneath the anterior portion of the zygomatic arch and provides for basal pterional exposure than that offered by the conventional technique. Excessive retraction of the temporalis muscle over the zygomatic arch can results in compromise of its vascular supply, which eventually heals by fibrosis. This technique is suitable for cases requiring pterional craniotomy and intended for the frontotemporal craniotomy requiring exposure of anterior portion of the temporal lobe and anterolateral skull base. However, this technique is not suitable for cases requiring extensive exposure like fronto-temporo-orbital zygomatic craniotomy, which requires exposure of the posterior most portion of the temporal lobe.
Temporalis fascia and pericranium is incised along with skin and subcutaneous tissue. Temporalis fascia and masseteric fascia is in continuity with periosteum at the bony attachment over zygomatic arch. Opening of subgaleal space is avoided from beginning and subfascial dissection is carried out to prevent facial nerve injury [Figure 2]a and [Figure 2]b. Temporalis fascia is separated from superior temporal line by sharp dissection. The use of diathermy is avoided to prevent thermal injury to the muscle and to the fascial layers. Temporalis fascia and frontal pericranium are closely approximated at the time of scalp closure restoring normal anatomy, which creates tense template for subcutaneous tissues of scalp thereby avoiding sinking of scalp along bony defect of the craniotomy edges, especially in the frontal region [Figure 4]d. Temporal region defect is covered by intact temporalis muscle and approximating temporalis fascia. Free bone flap is anchored with hitch sutures to the temporalis fascia/pericranium avoiding requirement of metal implants for bone fixation. This technique provides excellent cosmetic results and is devoid of any temporalis muscle related complications. Avoidance of developing subgaleal space and approximation of temporalis fascia and pericranium is a critical step in preventing subgaleal collection and periorbital edema in immediate postoperative period [Figure 4]e. Follow-up at 6-month interval showed excellent functional preservation of temporalis muscle without any complications, viz. atrophy, chewing difficulty, trismus or any facial deformity.
Antegrade, subgaleal, subfascial, and subperiosteal dissection techniques of temporalis muscle elevation without any direct incision in its bulk enable neurovascular and muscle bulk preservation. Posterior maneuvering of elevated temporalis muscle with the “out rolling” or “in-rolling” technique is easy, quick, and provides adequate exposure during pterional craniotomy. Opening and closing of scalp layers without violating subgaleal space prevents subgaleal hematoma and periorbital edema in the postoperative period. Dissection in precise anatomical planes as described enables facial nerve and temporalis muscle bulk preservation avoiding delayed complications in long run with excellent cosmesis.
We would like to thank Dr. Antony Thomas, Department of Neurosurgery, RMSH, Kimberley, South Africa for the excellent illustrative figures. The authors would like to thank following faculty members from the Department of Forensic medicine: Dr. Ravindra B. Deokar, Associate Professor. Assistant professors Dr. Shahank Tyagi, Dr. Sachin Sudarshan Patil, Dr. Girish Vijay Tasgaonkar, Dr. Mahendra Namdeo Wankhede, Dr. Vikas Premlal Meshram, Dr. Manoj Bhausaheb Parchake, and Dr. Harshwardhan Khartade. The authors would also like to thank Dr. Ravikumar Kamble and Dr. Abhijeet Hosmani for their wholehearted support.
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Conflicts of interest
There are no conflicts of interest.
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