Atlas of Surgical Operations, Parotidectomia - Zollinger
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Transcript of Atlas of Surgical Operations, Parotidectomia - Zollinger
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Zollinger's Atlas of Surgical Operations > Additional Procedures >
PAROTIDECTOMY, LATERAL LOBECTOMY
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Figure 6
Figure 7
Figure 8
INDICATIONS
Tumors are the most frequent indication for surgical exploration of the parotid
gland. Most are benign mixed tumors that arise in the lateral lobe and are treated
with wide excision, including a margin of normal tissue to prevent local
recurrence. Exploration of the parotid area must include careful identification of
the facial nerve and its branches, thus avoiding the major complication of facial
nerve palsy. Malignant tumors are also seen and require a wide excision, which
may include all or a portion of the facial nerve if it is involved. Lesions of the
medial lobe may necessitate a total parotidectomy; a superficial parotidectomy is
carried out first to identify and preserve the facial nerve before the medial lobe is
explored.
PREOPERATIVE PREPARATION
It is essential that all patients undergoing parotid surgery be made aware of the
possible loss of facial nerve function, with its resultant functional and cosmetic
consequences. Men should shave themselves early on the morning of surgery;
the hair about the ear may be cleared by the surgeon before draping.
ANESTHESIA
Oral endotracheal anesthesia with a flexible coupling is utilized so that the
anesthesiologist may be located at the patient's side, thus giving the surgeon
adequate room. A short-acting muscle relaxant should be used for the
endotracheal intubation. This allows the surgeon to identify motor nerves by
direct stimulation (gentle pinch) during the dissection.
POSITION
The patient is positioned on his or her back, and the face is turned to the side
opposite the lesion. The head and neck are placed in slight extension, and the
head of the table is elevated to reduce venous pressure in the head and neck.
OPERATIVE PREPARATION
After appropriate skin preparation with detergents and antiseptic solutions, sterile
towel drapes are positioned to allow visualization of the entire ipsilateral side of
the face.
INCISION AND EXPOSURE
The incision is carried in the crease immediately in front of the ear, around the
lobule and up in the postauricular fold (Figure 1). It then curves posteriorly over
the mastoid process and swings smoothly down into the superior cervical crease.
The superior cervical crease is located approximately 2 cm below the angle of the
mandible. It should be remembered that with the patient's neck extended and
head turned to the side, the facial skin is pulled down onto the neck, and the
incision should be made low enough that when the patient's head is returned to
normal position, the incision does not lie along the body of the mandible. No
incisions are made on the cheek itself. The cervical-facial skin flap is then
elevated with sharp dissection to expose adequately the area of the tumor. This
elevation takes place to the anterior border of the masseter muscle. A traction
suture may be placed through the earlobe to hold this out of the operator's visual
field (Figure 2). The masseteric parotid fascia has then been exposed, and the
parotid gland can be seen within its capsule, bounded superiorly by the cartilages
of the ear, posteriorly by the sternocleidomastoid muscle, and medially by the
digastric and stylohyoid muscles.
DETAILS OF PROCEDURE
The surgeon must understand clearly the surgical anatomy of the facial nerve.
The main trunk of the facial nerve emerges from the stylomastoid foramen. It
courses anteriorly and slightly inferiorly between the mastoid process and the
membranous portion of the external auditory canal. The main trunk of the nerve
usually bifurcates into the temporofacial and cervicofacial divisions after it enters
the gland, but occasionally this occurs before entrance. The parotid gland is
commonly described as being divided into superficial and deep lobes, the nerve
passing between the two. These lobes are not anatomically distinct, because the
separation is defined by the location of the nerve, which actually passes directly
through the glandular parenchyma. The cervicofacial division bifurcates into the
small platysmal or cervical branch and the marginal mandibular branch at the
inferior margin of the gland. The latter courses within the platysma muscle just
inferior to the horizontal ramus of the mandible, where it innervates the lower lip.
Whereas most other branches of the facial nerve have numerous cross-
anastomoses, the marginal mandibular branch has none; therefore division of this
branch will always result in paralysis of half of the lower lip. Identification of the
marginal mandibular branch before the main nerve trunk is defined is facilitated
by the fact that 97 percent of the time it lies superficial to the posterior facial
vein.
The buccal zygomatic division emerges from the anterior margin of the gland with
numerous filamentous branches that innervate the muscles of facial expression,
including the periorbital muscles and circumoral muscles of the upper lip. The
temporal branch runs superiorly and innervates the frontal muscles. This branch
has poor regenerative potential and no cross-anastomosis; injury to it will lead to
permanent paralysis of the frontalis muscle.
The safest way of identifying the facial nerve is to locate and expose the main
trunk. The anterior border of the sternocleidomastoid muscle is identified, as are
the posterior facial vein and the greater auricular nerve, in the inferior portion of
the incision (Figures 2 and 3). The capsule of the parotid gland then is mobilized
from the anterior border of the sternocleidomastoid muscle, and dissection is
carried down in an area inferior and posterior to the cartilaginous external
auditory canal.
Several landmarks are utilized here in the search for the main trunk of the facial
nerve. The sternocleidomastoid muscle is retracted posteriorly and the parotid
gland anteriorly. The posterior belly of the digastric can be visualized as it pushes
up into its groove (Figure 4), and the nerve lies anterior to this. The membranous
portion of the canal is the superior landmark, and the nerve lies approximately 5
mm from the tip of this cartilage. By using these landmarks as well as a Faradic
stimulator or gentle mechanical stimulation with forceps, the surgeon safely can
locate the main trunk of the nerve (Figure 5). If mechanical stimulation is used,
the instruments must not be clamped firmly on the tissue as a form of testing,
but rather the tissue should be pinched gently as the muscles of the face are
observed for motion. If an electrical nerve stimulator is used, it must be tested
regularly to be certain that it is functioning in each test situation. A final landmark
is a branch of the postauricular artery just lateral to the main trunk of the facial
nerve. If the position or bulk of the tumor makes exposure of the main trunk of
the facial nerve difficult, it may be identified distally. As indicated previously, the
marginal mandibular branch lies superficial to the posterior facial vein in most
circumstances. The buccal branch lies immediately superior to Stensen's duct,
and identification of this duct will lead the operator to the buccal branch of the
nerve. Dissection from distal to proximal must be carried out carefully, because
the junction of other branches of the nerve may not be seen as easily as divisions
of the nerve when the dissection is carried out in the opposite direction.
Numerous methods have been described for freeing the gland from the nerve.
The safest dissection technique is the hemostat-scissors dissection. By dissecting
bluntly with a fine hemostat and then cutting only the tissue exposed in the open
jaws, the surgeon can protect the nerve (Figure 6). The gland may be elevated
by clamping the tissue or by the use of holding sutures, and the two major
divisions of the facial nerve are identified. Dissection may proceed anteriorly
along any or all of the major divisions, depending upon the tumor's position.
Since the majority of tumors occur in the lower portion of the lateral lobe, the
upper segment of the gland is usually mobilized first (Figure 7). A moderate
amount of bleeding may be expected, but this will be controllable with finger
pressure, electrocoagulation, or fine ligatures. Once the tumor has been freed
from the facial nerve, Stensen's duct will appear in the midanterior portion of the
gland (Figure 8). Only the lateral lobe tributary is ligated, because medial lobe
atrophy will occur if the main duct is tied. After removal of the lateral lobe, the
isthmus and the medial lobe remain deep to the facial nerve; they will appear as
small islands of parotid tissue and should represent only 20 percent of the total
parotid gland. The lobe may be transected when the tumor and a surrounding
portion of normal tissue have been completely separated from the facial nerve.
CLOSURE
The wound is thoroughly irrigated and meticulous hemostasis obtained. A small
perforated closed-suction Silastic catheter may be brought up through a stab
wound and attached to a suction apparatus. The subcutaneous tissue is
approximated with fine absorbable sutures followed by adhesive skin strips.
POSTOPERATIVE CARE
Temporary paresis from traction on the facial nerve may occur and usually clears
in a few days to a week. If the greater auricular nerve has been divided in the
course of the procedure, anesthesia in its distribution will be permanent.
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