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ORIGINAL
Surgical training in video-assisted neck surgery-based
thyroidectomy using fresh frozen human cadavers
Mariko Aoyama1, Hiromitsu Takizawa1, Mitsuhiro Tsuboi1, Shinichi Yamasaki2, Yoshihiro Tsuruo3, and Akira Tangoku1
1
Department of Thoracic, Endocrine Surgery, and Oncology ; Institute of Health ; Biosciences ; The University of Tokushima, Tokushima,
Japan, 2Department of Surgery, Tokushima Municipal Hospital, Tokushima, Japan, 3Department of Anatomy and Cell Biology ; Institute ofBiomedical Science ; Tokushima University Graduate School, Tokushima, Japan

Abstract : Endoscopic surgery has been introduced in various surgical fields. Endoscopic surgery requires different skills from open surgery due to the restricted surgical field and difficulty in identifying anatomical structuresfrom certain viewpoints. Therefore, surgeons need to undergo sufficient surgical training before performing
such surgery in the clinical setting. We examined the utility of fresh frozen human cadavers for surgical training aimed at introducing video-assisted neck surgery (VANS) at our department. First, we performed surgicaltraining using fresh human cadavers four times. Next, we performed hemi-thyroidectomy with VANS in 5 clinicalpatients. After the cadaver training and the actual surgery, the surgeons evaluated each step of the surgical procedure using a 3-point scale. In the cadaver training, the scores for steps : creation of a subcutaneous tunnel andlifting up the skin flap and pre-thyroid muscles were higher than other steps. And a tracheal injury occurred as acomplication. However, we were able to recognize anatomical structures under the endoscopic view. And it wasalso useful for confirming the role of surgical staff and simulating the placement of surgical equipment. Surgicaltraining using fresh frozen human cadavers was effective at introducing a new surgical method. J. Med. Invest.
66 : 293-296, August, 2019
Keywords : video-assisted neck surgery, fresh frozen human cadaver, thyroidectomy

BACKGROUNDSUBJECTS AND METHODSVideo-assisted neck surgery (VANS) for the treatment ofthyroid tumors was reported by Shimizu in 1999 (1), and VANS
for thyroid disease has been covered by the Japanese health insurance system since 2016. Compared with open surgery, VANS
produces superior cosmetic results because the surgical wound is
not noticeable (1, 2). As thyroid disease exhibits a predilection forfemale patients, VANS is expected to become a standard surgical method in future.
The endoscopic approach requires different skills from open
surgery because it involves a restricted surgical field and difficulty in identifying anatomical structures from certain viewpoints.
In order to allow surgeons to learn how to perform endoscopic
surgery safely, skill-training laboratories and simulation models, for example, box trainers, virtual reality simulations, andanimal models, have been developed (3-5). Fresh frozen humancadavers are a useful resource for endoscopic surgical training,as they offer excellent handling fidelity and normal anatomical
relationships. Our institution has some facilities that offer training in basic endoscopic skills and simulations that closely matchthe situations found during clinical surgery.
We evaluated the usefulness of surgical training using fresh
frozen human cadavers as a tool for VANS training.

We (three certified board surgeons of the Japan Surgical Society) performed VANS training using two fresh frozen humancadavers. The cadaver training was undertaken with the approval of our institution’s ethics committee and was conductedaccording to the Guidelines for Cadaver Dissection in Education
and Research of Clinical Medicine (Japan Society and Japanese
Association of Anatomists).
After the training, we performed VANS in 5 patients. All of
the patients were female, and their mean age was 40 (range : 17to 68). The preoperative diagnosis was adenomatous goiter in
3 cases and follicular tumor in 2 cases. All patients underwent
hemi-thyroidectomy. All surgical procedures involved the sameprocedure as was performed on the cadavers. After the cadavertraining and the actual surgery, the three surgeons evaluatedeach step of the surgical procedure using a 3-point scale (1 : thecadaver training was not useful, 2 : neither 1 nor 3, 3 : the cadaver training was useful).

Received for publication April 9, 2019 ; accepted June 12, 2019.
Address correspondence and reprint requests to Mariko Aoyama, Department of Thoracic, Endocrine Surgery, and Oncology ; Institute of
Health ; Biosciences ; The University of Tokushima ; 3-18-15 ; Kuramoto-cho ; Tokushima ; 770-8509 ; Japan and Fax : +81-88-633-7144.

SURGICAL PROCEDURE
Training models were established using fresh human cadavers. The two fresh cadavers, one female and one male, wereplaced in the supine position. The surgical team consisted of asurgeon, an assistant, and a scopist. The surgeon stood on theaffected side, and the assistant and the scopist stood on the otherside. A monitor was placed over the head of the cadaver. A 3.0cm subclavian incision was made for the main operation. A 1-cm
incision was made within the boundaries of the original incision,and a 5-mm trocar and a 5-mm, 30° rigid scope (Karl-Storz,Germany) were inserted.
Eight steps evaluated for the surgical procedure are thefollowing.

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1)Creation of a subcutaneous tunnel : Surgical dissection, including the release of connective tissue and the division of bloodvessels, was performed using a 20-cm-long THUNDERBEAT(inline grip type ; OLYMPUS, Japan). A subcutaneous tunnel
to the anterior neck region was created over the clavicle. The
pre-thyroid muscles were exposed. The surface of the thyroid
lobe was identified and separated from the muscles. 2) Lifting
up the skin flap and pre-thyroid muscles : The skin-muscle
flap was lifted up using a Kirschner wire and a suture to create a working space. 3) Separating the thyroid lobe from thepre-thyroid muscle : The lateral surface of the thyroid lobe wasexposed, and the middle thyroid vein was cut. 4) Dissecting thesuperior thyroid pole and blood vessels : Next, the blood vesselsof the superior thyroid pole were dissected, and the superior
parathyroid gland was identified. 5) Identifying and preserving
the recurrent laryngeal nerve : The recurrent laryngeal nerve
was identified and preserved. 6) Identifying and preserving theparathyroid glands : We continued towards the inferior pole,and the inferior parathyroid gland was identified. 7) Dissecting
the isthmus : The isthmus was separated from the trachea anddissected. 8) Resecting the thyroid lobe from the trachea : The
thyroid lobe was removed from the trachea. The released thyroid
gland was removed through the 3.0-cm-long incision.

RESULTSWe performed hemi-thyroidectomy via VANS a total of fourtimes ; i.e., twice in each fresh frozen human cadaver. The scores
awarded for each step of the surgical procedure by the three expert surgeons are shown in Table 1. The scores for steps 1 and 2
were higher than those for the other steps. The skin and musclesof the fresh frozen human cadaver models were in almost thesame state as those of the clinical patients (Figure 1). The scoresfor step 5 were also high. In one of the four training procedures,the recurrent laryngeal nerve could not be clearly identified.
However, in the rest of the training procedures, it could be identified and preserved (Figure 2). The scores for steps 7 and 8 werelower than those for the other steps. A tracheal injury occurred
during the cadaver training.
We performed hemi-thyroidectomy via VANS in 5 patients(Table 2). None of the patients underwent conversion to opensurgery. The mean operative time was 159 minutes (120–190minutes). In all cases, the recurrent laryngeal nerve and parathyroid glands were identified and preserved. No complications
were encountered, and the mean duration of the patients’ hospital stays was 5 days (4–7 days). And we compared the outcomeof surgery between VANS and conventional open surgery at thesimilar period (Table 3). The mean tumor sizes in the conventional open surgery was bigger than in the VANS. And the mean
operation time was shorter than VANS.

Table 1. The scores awarded by the three expert surgeons for each step of the surgical procedureFigure 1. Left hemi-thyroidectomya) Endoscopic view of a fresh frozen cadaver model b) Endoscopic view of a clinical patient* : sternocleidomastoid muscle, ** : pre-thyroid muscles

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Figure 2. Left hemi-thyroidectomy. The arrow points to the recurrent laryngeal nerve.

a) Endoscopic view of a fresh frozen cadaver model* : trachea, ** : left thyroid lobeb) Endoscopic view of a clinical patient

Table 2. Five patients in which hemi-thyroidectomy was performed using VANS

Table 3. The outcome of VANS and conventional open surgery

DISCUSSION
Endoscopic surgery requires different skills from conventional
surgery, and training programs that allow surgeons to learnsuch technical skills are needed. Skill-training laboratories andvarious simulation models have been developed, such as drybox simulators, virtual reality simulators, and animal models(3-10). In Japan, the publication of the “Guidelines for Cadaver
Dissection in Education and Research of Clinical Medicine” in2012 confirmed that surgical training using cadavers is lawful,providing it is conducted under adequate supervision and appropriate rules (3, 6). Therefore, some medical universities havestarted to perform surgical training using human cadaver models (3). Due to their fidelity and anatomy, human cadavers are auseful resource for surgical training (4, 6-8).
There are various methods that can be used to preserve
human cadavers. Compared with cadavers subjected to otherpreservation methods, such as formalin fixation and Thiel’s
method, fresh frozen cadavers exhibit a more life-like color andgreater softness and pliability (3). In addition, surgical training
using fresh frozen cadavers is more realistic in terms of theproximity of other viscera, tissue compliance, and depth percep-tion (3). Many studies have used fresh frozen cadavers, and thevalidity of laparoscopic training using fresh frozen cadavers hasbeen confirmed (5, 8).
VANS for benign thyroid disease and cancer has been coveredby the Japanese health insurance system since 2016 and 2018,respectively. We performed VANS training using fresh frozen
human cadavers and evaluated its usefulness.
The fresh human cadavers were preserved in a good condition,and their tissues and organs exhibited flexibility and plasticity,
especially the skin and muscles. In fact, they were in almost thesame state as those of the clinical patients. Therefore, training
using cadaver models seemed to be very useful for learning how
to perform certain procedures ; i.e., creating a subcutaneous
tunnel and lifting up the skin flap and pre-thyroid muscles. A
sufficient working space was provided (similar to that found inin vivo conditions) during the cadaver training. The scores fortwo steps (forming the subcutaneous tunnel and lifting up theflap) were higher than those for the other steps. In the cadavermodels, the recurrent laryngeal nerve could be clearly identified,
and the tissue around it was preserved in a good condition. Thus,
the use of cadavers was useful for training regarding the identification of the anatomical position of the recurrent laryngeal

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nerve. It was also useful for confirming the role of surgical staff
and simulating the placement of surgical equipment.
In the actual surgical cases, there were no complications, andso simulations using cadaver models might reduce the risk ofsurgical complications.
However, there are some issues with the use of fresh frozen
cadavers. First, the thyroid tissue of cadaver models is denatured
compared with that found in clinical patients. The boundarybetween the thyroid gland and the surrounding tissue is alsounclear. Therefore, it is difficult to separate the thyroid fromthe surrounding organs, such as the pre-thyroid muscles andtrachea, and to expose the superior thyroid pole. In the present
study, the scores for two steps ; i.e., the separation between the
thyroid gland and the surrounding tissue and dissecting thesuperior thyroid pole, were lower than those for the other steps.
As cadavers undergo rapid putrefaction after thawing, freezers
are required for their storage, and it is necessary to perform theplanned training within a limited period (3). In addition, the costof fresh frozen cadaver model training is higher than training
using cadaver models that are preserved using other methods,
such as formalin fixation, Thiel’s method, or the saturated salt
solution method (3). We should consider combining other training methods to reduce costs and ensure that training time isused effectively.

CONCLUSION
Fresh frozen human cadavers are an excellent tool for surgicaltraining aimed at teaching the VANS technique. Furthermore,such training could be used to introduce new surgical methodssafely.

CONFLICT OF INTERESTS
The authors declare that there is no conflicts of interests regarding the publication of this paper.

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