EMBRYOLOGY
The paired submandibular
glands develop from the buds in the floor of the primitive mouth that grow on
the lateral aspect of the tongue. The buds initially give rise to cords that
canalize into ducts, and their ends differentiate into the acinar
structures.
ANATOMY
The submandibular gland
is located in the floor of the mouth and consists of a larger superficial part
that communicates with a smaller deep part around the posterior border of the
mylohyoid. The superficial part primarily lies within the digastric triangle and
is bounded superomedially by the mylohyoid muscle, superolaterally by the
mandible, and inferiorly by the skin platysma and investing layer of the deep
cervical fascia. The facial artery is related to the posterior surface of the
submandibular gland.
The deep part of the
submandibular gland is located in the interval between the mylohyoid and the
hyoglossus muscle. Emerging from the deep part of the gland is the submandibular
duct (Wharton’s duct), which opens at the base of the frenulum in the floor of
the mouth. Other important structures that lie in the vicinity of the deep part
of the submandibular gland are the lingual nerve, the submandibular ganglion
superiorly, and the hypoglossal nerve inferiorly.
The blood supply of the
submandibular gland is through branches of the facial and lingual arteries, and
the venous drainage follows the respective facial and lingual veins. The parasympathetic secretomotor
supply is from the superior salivary nucleus of the seventh cranial nerve. These
fibers reach the submandibular ganglion via the chorda tympani and submandibular
ganglion.
PREOPERATIVE PREPARATION
Apart from basic
investigations, the imaging studies of the submandibular gland, particularly
plain radiograph of the floor of the mouth, sialogram for recurrent
submandibular gland enlargement, or computed tomography of the neck for a
solitary mass within the submandibular gland, are reviewed. Although indication
for resection of the submandibular gland is usually based on clinical suspicion,
results of fine-needle aspiration cytology, if performed, should be reviewed.
Preoperatively the surgeon must determine by physical examination whether the
hypoglossal, lingual, and marginal mandibular branches of the facial nerve are
intact. Informed consent is obtained after the patient is informed about the
risks of damage to the hypoglossal nerve, the lingual nerve, and the marginal
mandibular branch of the facial nerve.
OPERATIVE PROCEDURE
POSITION
The patient undergoes
general anesthesia with endotracheal intubation, but anesthesiologists must
refrain from using paralyzing agents because these may make the use of the nerve
stimulator ineffective. The patient is placed in a supine position with a
shoulder roll to extend the neck. The head is turned away from the affected side
and elevated to a 45-degree position to reduce venous congestion. The operative
area is prepped and draped. The face is left exposed by placing a transparent
dressing to allow facial movements to be observed during facial nerve
stimulation.
INCISION
Fig. 1 |
An incision about 2 cm
below and parallel to the body of the mandible is marked with an indelible pen (
Fig. 1). The skin is
infiltrated with 1% lidocaine with epinephrine to avoid bleeding from the skin.
The skin is incised with a no. 15 scalpel.
EXPOSURE AND OPERATIVE TECHNIQUE
The dermis is divided
with cutting electrocautery down to the level of the platysma. In line with the
incision, the platysma is also divided, and then superior and inferior flaps are
created in the subplatysmal plane. Superiorly, the surgeon should be cognizant
of the presence of the marginal mandibular branch of the facial nerve. The
facial artery and vein will be encountered running deep to this nerve, and they
are divided and ligated. In fact, retracting these vessels upward will protect
the marginal mandibular branch of the facial nerve during subsequent dissection
(Hayes-Martin maneuver). The superior border of the gland is freed from the body
of the mandible.
Dissection now proceeds
toward the posterior aspect of the gland, and the posterior/common facial vein
is exposed, isolated, divided, and ligated. Posteriorly, the gland is carefully
elevated off the surface of the sternocleidomastoid muscle. Retracting the
anterior border of the sternocleidomastoid muscle will expose the tortuous
facial artery, which is ligated again. The superficial part of the submandibular
gland is elevated from the underlying mylohyoid muscle. The posterior border of
the mylohyoid muscle is identified and then retracted anteriorly with a loop
retractor. This should expose the deep part of the submandibular gland and the
important adjacent structures ( Fig. 2 ). These include the lingual
nerve above and the hypoglossal nerve below.
Fig. 2 |
Superiorly the branches
from the lingual nerve to the submandibular ganglion are seen and divided. This
allows the lingual nerve to retract superiorly and thus avoids injury. Next, the
hypoglossal nerve, which will be seen emerging from beneath the anterior belly
of the digastric muscle, is identified. The gland now remains attached only by
its submandibular duct (Wharton’s duct), lying between the lingual and
hypoglossal nerves. The submandibular duct is clamped, divided, and ligated with
2-0 absorbable sutures. The operative area is inspected for hemostasis, and the
retracted marginal mandibular nerve is returned to its normal
position.
CLOSURE
A 7-mm Jackson-Pratt
drain is placed in the operative field. The platysma is approximated, with care
taken not to entrap the already preserved marginal mandibular nerve. The skin is
closed with 5-0 absorbable sutures.
Source : Khatri, VP. 2003. Khatri : Operative Surgery Manual. Vol. 1st Ed. Elsevier. USA
Video : http://www.youtube.com/watch?v=T6jmyRAmTBA
No comments :
Post a Comment