Subtotal Thyroidectomy

Description
General anesthesia is used. Subtotal thyroidectomy is the removal of greater than
90 % of the thyroid gland, leaving the posterior aspects of the gland, and is used
for patients with hyperthyroidism due to diffuse hyperfunction, or rarely for multinodular
goiter. The nature of the pathology has almost always been determined
prior to surgery.
The thyroid gland is usually diffusely enlarged, and hyperthyroidism
may produce a range of different clinical features, which may infl uence the
incidence of complications. The patient is supine with a roll placed transversely
under the scapulae to allow optimal neck extension. To prevent neck hyperextension,
the head is supported on a supporting “donut” head ring. A curved transverse
“skin crease” incision is made in the anterior neck about two fi ngerbreadths above
the clavicular heads, continuing deep to the platysma muscle. The strap muscles are
separated in the midline and retracted laterally. Each thyroid lobe is sequentially
mobilized anteriorly and medially by transecting vessels laterally. This exposes the
thyroidal vessels and fi ne attachments of Berry’s ligament. The vessels supplying
the thyroid must be dissected carefully and divided as close to the gland as possible
(extracapsular dissection). The major portions of both thyroid lobes are removed
with the isthmus, to leave a posterior cuff of each lobe of thyroid on each side.
The size of the retained portion of thyroid is critical to creating euthyroid function,
while alleviating hyperthyroidism. One of the aims of subtotal thyroidectomy is
to transect the thyroid gland away from the upper and lower parathyroid glands
and the recurrent laryngeal nerve and the external branch of the superior laryngeal
nerve. Thus, theoretically avoiding risk to these structures. The recurrent laryngeal
nerve is most easily identifi ed where the inferior thyroid artery crosses it, but
the nerve may be anterior, posterior, or between branches of the artery, unless it is
nonrecurrent. The nerve should be followed until it enters the larynx. Great care
should be taken to avoid injury from too much traction, direct pressure, or electrocautery.
The use of nerve monitoring devices may improve the localization and
detection of nerve branches to preserve. In practice, many surgeons regard a careful
total thyroidectomy as almost as safe as a subtotal resection and preferable.
Anatomical Points
The thyroid gland arises from the foramen caecum of the posterior base of the
tongue and descends in the midline of the neck to reach the 2nd tracheal ring in
the adult. Variations in the course of the recurrent laryngeal nerve, typically on
the right side, occur in about 1 % of cases. The nerve may be anterior, posterior,
or between branches of the inferior thyroid artery. The right subclavian artery
can arise directly from the descending aorta so that the right nerve is “nonrecurrent,”
exiting from the vagus nerve at a 45° angle. The nonrecurrent nerve may
be mistaken for a vessel and divided, resulting in paralysis of the ipsilateral vocal
cord. About 0.2 % of patients have both a recurrent and nonrecurrent laryngeal
nerve on the right. Left- sided “nonrecurrent” laryngeal nerves are very rare and
are seen with situs inversus. The course of the superior laryngeal nerve, including
its external and internal branches, is also variable. The external branch of the
superior laryngeal nerve is usually closely associated with the inferior pharyngeal
constrictor and may be covered entirely by its muscle fi bers. In 15 % of patients
the nerve travels with the superior thyroid artery. In 6 % of patients it continues
to accompany the superior thyroid artery even after branching of the main trunk.
During embryogenesis, the parathyroid glands migrate a great distance, and their
anatomical location may vary greatly. The presence of a large thyroid nodule may
further complicate the identifi cation of these structures, and it takes great patience
and tenacity to identify them. Fifteen percent of patients have more than four
parathyroid glands. The inferior parathyroid glands arise from the third pharyngeal
pouch and are closely associated with the thymus. As they migrate during
development, they may fi nally rest anywhere from the pharynx to the posterior
mediastinum. The superior glands are more reliable in their position because they
arise from the fourth pharyngeal pouch along with the lateral thyroid. Intrathyroid
parathyroids occur in about 1 % of patients. Some patients have large pyramidal
lobes of the thyroid. Other variations include lingual thyroid and thyroglossal duct
cysts.
Perspective
Bleeding is more common with a hypervascular thyroid gland, even
after oral iodine pretreatment which can render the gland fi rmer. Drains rarely
provide adequate drainage if the bleeding is heavy. Severe bleeding can cause
tracheal compression and acute respiratory failure, requiring prompt recognition,
surgical decompression, and control of bleeding. However, the major risk
from subtotal thyroidectomy is inadvertent damage to the recurrent or superior
laryngeal nerves. Any damage may not be apparent until any vocal cord swelling
from the endotracheal tube settles on the second or third postoperative day.
Intraoperative electromyography electrode monitoring may reduce the incidence
of recurrent laryngeal nerve injury. Bilateral recurrent laryngeal nerve injury is
a rare but particularly devastating complication. Injury occurs by traction, pressure,
or cautery. The patient will inevitably require a tracheostomy acutely for
airway management. Some patients require a permanent tracheostomy, but some
recover function or are able to manage their airways after vocal cord injections.
This injury is psychologically diffi cult for the patient to endure. Damage to both
parathyroid glands is not common because the posterior parts of the gland are
not resected. Hypocalcemia is due to temporary or permanent disruption of normal
parathyroid function. This may be due to manipulation of the blood supply,
direct trauma to the glands, or removal of the glands. Most hypocalcemia is transient,
and the glands will resume function after several days or weeks. Patients are
treated with calcium supplementation until the parathyroids resume function. If
the glands have been permanently injured or removed, the patient will require lifelong
calcium and vitamin D supplementation. Thyroid storm (crisis) is exceedingly
rare with adequate preoperative preparation, but potentially life threatening
if it occurs. Horner’s syndrome is very rare, caused by retraction damage to the
cervical sympathetic chain. It usually resolves, but can be permanent. Cutaneous
numbness and tingling of the anterior neck is common and due to division of cervical
plexus branches during incision. It often improves with time, but can make
shaving and application of cosmetics diffi cult. Neck wounds usually heal rapidly
with low infection risk and are rarely unsightly. Keloid reaction at the scar may
occur being diffi cult to prevent or treat.
Major Complications
A serious complication is damage to the recurrent laryngeal nerve or to the
external branch of the superior laryngeal nerve. Some factors for increased risk
or nerve injury are the inexperienced surgeon, invasive malignancy, very large thyroid
masses, and reoperative surgery. With time the changes in phonation associated
with these injuries will often improve; however, in patients who depend on their
voice for a livelihood, the injuries can be devastating. Management of a divided
recurrent laryngeal nerve is controversial. Anastomosis of the nerve restores some
bulk to the vocal cord; however, there is anomalous regeneration, and phonation
may not return to normal. When the recurrent laryngeal nerve is known to be intact,
the patient should be referred for a trial of speech therapy. Injection of material (e.g.,
gelatin, Tefl on, Silastic fat) into the vocal cord(s) may be helpful in voice restoration.
In some cases, regardless of the integrity of the nerve, medialization thyroplasty
(using a variety of methods) may be indicated to improve the vocal quality
and decrease aspiration. There is little that can be done to restore the integrity of
a damaged external branch of the superior laryngeal nerve. Pre- and postoperative
videostrobic testing can be useful in defi ning preexisting or surgically induced voice
and laryngeal functional changes. Transient mild hypocalcemia is not uncommon
after surgery. Major hypocalcemia in the postoperative period is indicative
of injury to the parathyroid glands , which is usually transient, but in <3 % cases
is permanent, although uncommon after a subtotal thyroidectomy because the posterior
aspects of the thyroid glands are less disturbed. Oral calcium and vitamin D
therapy for several weeks usually corrects this and is then reduced to test for recovery.
Meticulous surgical technique, sometimes with autotransplantation, can almost
prevent this complication. Serious postoperative bleeding <48 h, requiring urgent
reoperative drainage, is a rare but well-recognized complication that patients should
be informed about. Thorough hemostasis and Valsalva testing before closure at the
completion of surgery are two risk reduction strategies often used. Thyroid storm
is very rare but serious. Infection and scar deformity with the need for revision
surgery are also uncommon.