Extra Cranial Facial Nerve Anatomical Dissection: Fresh Tissue Vs Embalmed Tissue

Anatomical topography of fmelewati gacial nerve is very important as one of basic knowledge for clinical application. Extra cranial facial nerve branches were difficult to identify because of their smaller size and lack of consistent landmark. Dissected skill need experience with various tissue, like fresh and embalmed tissue. This study was aimed to compare the facial nerve anatomical dissection by using fresh tissue and embalmed tissue cadaver. Three fresh tissue cadaver from Forensic Department and three embalmed tissue cadaver (after 2 months preservated by ethanol) from laboratorium Anatomy Department were used to anatomical dissection the topography of extra cranial facial nerve. Incisi line started from midline across the glabella,tip of the nose until philtral groove. Skin flap from midline to lateral until we find the branches of facial nerve. The anatomical dissection of extra cranial facial nerve from 3 embalmed tissue can provide dissected facial nerve and it”s branches. But it is hardly difficult to separate the skin from Superficial Musculo Aponeurotic System (SMAS) compared with fresh cadaveric tissue. Embalmed cadaver and fresh tissue from post mortem body can be used for anatomical dissection study of extra cranial facial nerve. Each different tissue has its own difficulties depends the aim of the dissection study.


Introduction
Facial nerve is a one of cranial nerve with longer pathway than another cranial nerve. It has intra and extra cranial (extra temporal) nerves. 1 Basic knowledge about topography facial nerve is very important, especially for clinician when they open face region, like parotidectomy, facial surgery and facial grafting. Facial nerve injury most commonly caused by variation branching itself. 2 Identification of the facial nerve could be performed through study of textbooks, virtual, or through direct dissection on cadaver. Study through dissection on the cadaver has highest value to students' understanding process of anatomy structure and its topography. Dissection as a part of medical studies' curriculum, as in bachelor or speciality program, has a particular implication to support understanding of topography and dissection skill in the future. 2 Development of dissection activity in medicine studies, is never apart from the advancement of cadaver's preservation. Techniques of cadaver development with formalin has been known and used in Anatomy department in almost all medical faculties in Indonesia. Formalin's effect that is not environmentally friendly, caused many of new developments in preservation like plastination, Thiel's method, and other formulas which are being developed in each of medicine studies especially in Anatomy department. Department of Anatomy, Physiology and Cell Biology Universitas Padjajaran has particular formula to cadaver preservation. This formula consist of mixture of formalin in small quantity, ethanol, glycerin and some other mixtures. The result of preservation with ethanol produces cadaver which is more flexible, moist and reduced smell of the formalin. 3 Dissection of extra temporal facial nerve could be done through anatomy dissection or surgical dissection. Other than having a very small size, topography and variation of the branches, facial nerve has its own uniqueness. Approach of anatomy dissection from midline part of the face through the lateral part in preauricular. The aim of this article is to pictures the topography and structure from extra temporal facial nerve through anatomy dissection on cadaver that has been preserved with ethanol compared with fresh cadaver that has not been preserved. 4,5

Material and Method
This study was approved and carried out by the guidelines of the Ethics Committee of Faculty Medicine Universitas Padjadjaran. This work was carried out at the Department of Biomedical Sciences and Department of Forensic and Medicolegal Hasan Sadikin Hospital. This study is a descriptive study with cadaver as a subject. Three face of cadaver samples ( 2 male and 1 female ) that has been preserved with ethanol of minimum of 2 months, and 3 face of cadaver samples ( 2 male and 1 female) that has not been preserved (fresh) from department of forensic studies RSHS Bandung. Two groups of cadaver is dissected on the midline part of the face to the lateral. Facial nerve is observed with loop glasses.

Steps of anatomy dissection of facial nerve:
The heads were turned lateral side to expose preauricular region for dissection.Firstly, incision is performed on the midline of the face from the border of hairline through glabella, highest point of the nose, philtral groove through thyroidea cartilage. Secondly, a skin flap is made from midline to lateral, continue with subcutis flap and SMAS from midline to lateral, identify the stylomastoid foramen, superficial parotid gland, tragus cartilage, angulus mandibular and digastric muscle. Then continue the procedure with identification of the facial nerve's main trunk. The length of facial nerve from main trunk to the tragus, angulus mandible, main branching and canthus lateralis were determined. We use a compass with a centimeter scale to measure distance and length. Step of anatomical dissection II : Incision continue from midline to lateral with separation of the layers, flapping from midline to lateral. Subcutis is separated from SMAS part from the lower part. Flapping is performed until the lateral. Fig. 3(A) and (B) are appareance condition of subcutaneus tissue from embalmed cadaver (different cadavers). Pointed arrow in Fig.3 (B) shows the trunk of facial nerve, which rigid and easily to identified. But layer of surrounded connective tissue (SMASH) difficult to separate. Fig. 1 and 2 are steps anatomical dissection in embalmed cadaver. In dissection with embalmed cadaver that is treated with ethanol, after separate the subcutis layer, the SMAS layer on the lower part is difficult to separate, but the facial nerve main trunk and its branches can be identified between two of the fascias on parotid gland layers (Fig. 3A and 3 B). The structure of the facial nerve appears more rigid so that it is more stronger in structural, not vulnerable compares to the fresh cadaver. This is might be caused by the effect of ethanol preservation effect.  In a dissection with fresh tissue, separation of the layers can easily be performed (Fig. 4). The layer of subcutis with SMAS on the lower part is easy to be released. The structure of the facial nerve is difficult to preserve, especially the main trunk which is located between the fascia on parotid gland. Extra care is needed to the preservation process.

The measurement
The exit of facial nerve from the skull through the stylomastoid foramen without exception in both 6 face cadavers and fresh tissue. The mean distance of the facial nerve trunk to the tragus, angulus mandible, main branching and canthus lateralis describe in table 1. This study revealed no significant correlation length of facial nerve from main trunk to the item structure measured between dissection using embalmed cadaver with fresh tissue from post mortem body.

Discussion
The trunk of facial nerve between stylomastoid foramen and its bifurcation is frequently dissected during surgery. Segment or part of Facial nerve which located in complex area anatomy must be clearly understood to prevent iatrogenic damage of facial nerve. Injury of facial nerve can cause palsy.
Identification of facial nerve trunk is hardly difficult because it´s surrounded dense connective tissue. The knowledge of dimension facial nerve are important for surgical procedure. Different condition tissue influence the structure of the nerve and surrounded connective tissue .
Embalmed cadavers are the primary tools for teaching anatomy. But changed color and texture of structure organs and hardening of connective tissue encountered difficulties of anatomical study and their perception of the nerve. Fresh cadaver and embalmed cadaver each has its own advantages and disadvantages. Fresh cadaver gives facial nerve's topography include layers of face's regio. On the other hand, embalmed cadaver, structure of the face is more difficult to layer separation, but the nerve structure appears more rigid, not vulnerable. So that for the students that needs skill advancement and understanding to facial nerve's anatomy topography structure of an anatomy dissection in fresh as well as in embalmed cadaver has its own advantages.

Conclusion:
Embalmed cadaver and fresh tissue from post mortem body can be used for anatomical dissection study of extra cranial facial nerve. Each different tissue has its own difficulties depends the aim of the dissection study. More studies about variation facial nerve topography in Indonesian people can be done by using combination of this method.