Thyroid surgery is a widely performed operation in recent two decades with complication rate less than 5% . Parathyroid damage is most frequent complication of thyroid surgery because parathyroid is near to or even inside of thyroid gland, and because it is a challenge to distinguish by naked eyes. It has been reported that the incidental rate of parathyroidectomy in thyroid surgery ranges between 6.4~31% . Incidental parathyroidectomy can cause mild to serious hypocalcemia which in turn impair quality of patient’s life. So it is important to protect parathyroid and to keep its’ normal function in thyroid surgery. There are several methods, which identify and protect the parathyroid glands in thyroid surgery, have been developed in the past several years and have being developed in recent years.
One parathyroid principle. This means to treat any parathyroid as the last one. One reason is that the number of parathyroid glands varies from 2 to more than 4 . The second reason is that it is not ensure not to damage other parathyroid glands. So all of the parathyroid glands identification is needed as possible as we can in the thyroid surgery. And meticulous dissection should be done to reserve the parathyroid glands and the main blood supply to them. The second meaning of one parathyroid principle is one parathyroid gland should be identified when thyroid surgery has been done to ensure not developing to permanent hypocalcemia.
Operation selection. The rate of incidental parathyroidectomy is associated with bilateral total thyroidectomy, central lymph node dissection  and experience of the surgeon. So if the lobectomy is enough, do not do the bilateral total thyroidectomy. The lower the experience of the surgeon has, the smaller the operation range should be done to reduce the rate of complications. As the better prognosis of thyroid cancer, the parathyroid glands damage should be well balanced with the recurrence of the cancer.
Anatomic location. Though the location of the parathyroid glands are varied, there are some common anatomic location clues can be tracked.
Relation to recurrent laryngeal nerve . The inferior parathyroid glands are consistently anterior to the recurrent laryngeal nerve, while the superior parathyroid gland is always posterior to the recurrent laryngeal nerve.
Relation to thyroid gland. Most parathyroid glands are tightly attached to the dorsal or lateral surface of thyroid lobes, often located in the fiber thyroid capsule between the natural and surgical coatings.
The lower corner of the thyroid cartilage . 85% of the superior parathyroid glands concentrates in the circle with a radius of 1cm area with the lower corner of the thyroid cartilage as the center.
Lower 1/3 of the junction of the posterior edge of the thyroid. More than 50% of the inferior parathyroid glands locates at this junction.
The normal parathyroid glands are usually not easily distinguishable from surrounding tissues such as droplets, lymph nodes, and thyroid nodules in thyroid surgery. There are some appearance features which can be helpful to identify parathyroid glands .
Size and thickness: The average diameter of normal parathyroid glands is 4-6mm, and the maximum diameter is rarely >8mm, while thyroid nodules are often about 10mm. The thickness of the parathyroid glands is much smaller than their length and width, usually at only 1-2mm, while the thickness of lymph nodes are more similar with length and width.
Color: Parathyroid glands are brown or yellowish
brown or tan, while lymph nodes are pink, fatty droplets are
Capsule: Parathyroid glands have a complete capsule
with some fatty tissues surrounded, while fatty droplets do
not have capsules.
Shape: Parathyroid glands have a smooth and regular
shape, while lymph node may have an irregular with an
Blood supply: Parathyroid glands are sensitive to blood
supply changes. When their arteries are damaged, they
become pale quickly, and when their veins are injured, they
become purple as congestion. But the fatty droplet, lymph
node and some thyroid nodules are not so sensitive to blood
Texture: The texture of the parathyroid glands is softer
than the lymph node, and harder than the fatty droplet.
With the anatomic location and appearance features, more
than half of the parathyroid glands can be identified by the naked
eye, while the identification of the rest of them needs additional
Here may be referred to carbon nanoparticles, which diameter
is about 150nm. When carbon nanoparticles have been injected
into the thyroid tissue, they will not enter the blood vessel, which
the clearance between capillary endothelial cells is 20-50nm, and
they will quickly enter the lymph vessels, which the gap between
capillary lymphatic endothelial cells is 120-500nm. Then the
thyroid, lymph node of the drainage area will be dyed black.
And the parathyroid glands will be not dyed black. So it makes
parathyroid glands readily being distinguished from thyroid and
lymph nodes. It is reported that carbon nanoparticles can help to
identify parathyroid, especially the inferior parathyroid glands,
and reduce the incidental parathyroidectomy in thyroid surgery
[7-8]. This expected situation needs well injection technique
with appropriate dosage to obtain best result. It cannot perfectly
dye all the lymph nodes which we want to remove. It may identify
the parathyroid glands only indirectly.
This is a remedy method to maintain part of the parathyroid
function in thyroid surgery [9-10]. When we found that the
parathyroid gland has been removed by mistake or the preserved
parathyroid gland has bad blood supply, the parathyroid gland
involved should be auto-transplanted. So routine examination
should be taken on the dissected thyroid and central tissues to
identify if parathyroid glands have been removed by mistake
before sending them to pathologist. When the tissue removed
cannot be identify whether it is parathyroid gland or other tissue,
half of it should be sent to intra-operation frozen pathology.
When this half has been identify to be parathyroid gland by
frozen section, the rest half should be auto-transplanted. Autotransplantation
can be done by particle entrapment into the
sternocleidomastoid or by homogenization injection into the
forearm muscles. It is reported that auto-transplantation of
the parathyroid glands can effectively reduce the rate of severe
postoperative permanent hypocalcemia.
Several studies on how to identify the normal parathyroid
intra-operatively have been processed in the recent years.
These studies are major in using some devices to detect the
auto-fluorescence of the parathyroid or fluorophores within the
Falco et al.  used near infrared light during thyroid and
parathyroid surgery, and found that mean parathyroid gland
fluorescence intensity (47.60) was significantly higher than the
thyroid gland (22.32) and background (9.27) (p < 0.0001). And
they found that the use of near infrared light for parathyroid
gland visualization significantly increased the number of
parathyroid glands identified. McWade et al. [12,13] used near
infrared light to detect the auto-fluorescence of the parathyroid
and surrounding tissues. They found that parathyroid glands
fluorescence was stronger (1.2-18 times) than that of the thyroid
with peak fluorescence at 822nm, and surrounding tissues
showed no auto-fluorescence. They also found that the accuracy
of this method to detect the parathyroid during thyroid surgery is
near 100%, though several factors may affect the signal intensity.
Original fluorescent detection apparatus used by Shinden et al.
 and optical coherence tomography used by Hou et al. 
showed that they can identify the parathyroid gland during
surgery easily and feasible. Auto-fluorescence detected by near
infrared light is an indirectly but promising method to identify
parathyroid in thyroid surgery.
Hyun et al.  demonstrated that using near-infrared
imaging system to detect the 700nm and 800nm halogenated
fluorophores after intravenous injection can identify the
parathyroid and thyroid glands in a high-sensitivity and
unambiguous mode in mice and pigs. Suh et al.  concluded that
indocyanine green NIR fluorescent imaging is useful to identify
parathyroid glands during thyroid surgery in dogs. Lavazza et al.
 reviewed that indocyanine green-enhanced fluorescence for
assessing parathyroid perfusion during thyroidectomy, and they
concluded that this method merits careful further evaluation for
use in thyroid surgery to identify the parathyroid glands by large
randomized prospective trials.
Other promising methods.There are several methods might
be used in the future to identify parathyroid glands such as
intraoperative measurements of intact parathyroid hormonethrough FNA , detecting the blood supply of parathyroid
glands by laser Doppler flow metryor oxygen spectroscopy.
There are some matured methods to really helpful to identify
and protect parathyroid glands in some degree in present, so we
need to practice these methods in thyroid surgery to minimize
the parathyroid injury. Some promising researches on how to
further identify the parathyroid glands have been processing.
The ideal methods may be
Applying some drugs to make the parathyroid being
easily identified by naked eye without additional device, or
Using a device which can tell us the pathologic diagnosis
of parathyroid in stainless,real time mode.
We are looking forward to clinical application of these
advance techniques to further prevent patients from
parathyroid damage in thyroid surgery.