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\begin{document}

\title{Preoperative simulation using three-dimensional printer in four temporal
bone surgeries}



\author[1]{Ichiro Fukumoto}%
\author[2]{Yukiyoshi Mita}%
\author[1]{Rie Shimmi}%
\author[1]{Yuri Sonobe}%
\author[1]{Tomohisa Iinuma}%
\author[1]{Kazuki Yamasaki}%
\author[1]{Shuji Yonekura}%
\author[3]{Toshimitsu Nemoto}%
\author[1]{Toyoyuki Hanazawa}%
\affil[1]{Chiba University Graduate School of Medicine School of Medicine}%
\affil[2]{Chiba University}%
\affil[3]{Japanese Red Cross Narita Hospital}%


\vspace{-1em}



  
  \date{June 15, 2024}


\begingroup
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\selectlanguage{english}
\begin{abstract}
It is difficult to anatomically understand the three-dimensional
structure of the middle ear and temporal bone during surgery, and great
surgical technique are required. Therefore, complications are avoided
through simulation using a three-dimensional printer, which was
effective in not only safe and reliable surgery but also educating young
physicians.%
\end{abstract}%



\sloppy


\textbf{Preoperative simulation}

\textbf{using three-dimensional printer}

\textbf{in four temporal bone surgeries}

Ichiro Fukumoto\textsuperscript{1}, Yukiyoshi Mita\textsuperscript{1},
Rie Shimmi\textsuperscript{1}, Yuri Sonobe\textsuperscript{1}, Tomohisa
Iinuma\textsuperscript{1}, Kazuki Yamasaki\textsuperscript{1}, Shuji
Yonekura\textsuperscript{1}, Toshimitsu Nemoto\textsuperscript{2},
Toyoyuki Hanazawa\textsuperscript{1}

1)Department of Otorhinolaryngology/Head and Neck Surgery, Chiba
University Graduate School of Medicine

2)Department of Otorhinolaryngology, Japanese Red Cross Narita Hospital

e-mail address

Ichiro Fukumoto:ichiro\_ichiro\_1124@yahoo.co.jp

Yukiyoshi Mita: mimitar@outlook.jp

Rie Shimmi: rie52@hotmail.co.jp

Yuri Sonobe: caxa1153@chiba-u.jp

Tomohisa Iinuma: iinuma-t@chiba-u.jp

Kazuki Yamasaki: k.yamasaki@faculty.chiba-u.jp

Shuji Yonekura: syonekura@faculty.chiba-u.jp

Toshimitsu Nemoto: nemopet1043@icloud.com

Toyoyuki Hanazawa: thanazawa@faculty.chiba-u.jp

Written informed consent was obtained from the patient to publish this
report in accordance with the journal's patient consent policy.

\textbf{Introduction}

The temporal bone is the most complicated site of the human body because
it is difficult to understand its three-dimensional anatomical
structures and involves many vital organs such as the facial nerve,
sigmoid sinus, middle cranial fossa, ossicular chain, cochlea,
vestibule, and semicircular canals\textsuperscript{1}. Therefore, ear
surgeries require extensive techniques, and a considerable number of
years and experience are needed to become ear surgeons. In addition,
having a prominent practiced hand in otology surgery is difficult and
surgical opportunities for young doctors are decreasing, due to the
increase in medical lawsuits. Consequently, many reports simulating
surgery using the temporal bone and temporal bone size of the original
model are available\textsuperscript{2}. However, institutions that allow
doctors to perform practice courses using real temporal bone are limited
because the procedure is legally complicated in Japan. Although temporal
bone models have realistic designs, there is a difference in drilling
bones during simulations, which is insufficient for surgical training.

Recently, several reported cases are available using three-dimensional
printers in the head and neck regions and during dental surgery,
particularly mandibular bone surgery\textsuperscript{3}. In the surgical
treatment of mandibular bone malignant tumors, particularly segmental
resection of the mandibular bone, rigid reconstruction is necessary
after tumor resection\textsuperscript{4}. Mandibular bone reproduction
using a three-dimensional printer is very useful because not only is the
simulation of tumor resection possible but also the creation of the
metal plate.

In 2016, additional surgical support can be calculated according to the
size of the original organ solid model for tumor resection of various
cancers in the head and neck regions in Japan. In our department,
preoperative simulation was performed using a three-dimensional printer
for not only mandibular bone malignant tumor surgery but also maxillary
malignant tumor surgery (maxillectomy, maxillary segmental resection),
anterior skull base surgery through an endoscopic approach, middle ear
surgery, and lateral skull base surgery. In this study, we reproduced
the temporal bone using a three-dimensional printer for middle ear and
temporal bone surgeries preoperatively and report the merits of our
department.

\textbf{Materials and Methods}

In four temporal bone surgeries, the temporal bone size of the original
model was reproduced using a three-dimensional printer preoperatively.
We created DVD-ROM copies of two-dimensional 0.5- to 1.0-mm computed
tomography (CT) slice images that were constructed into
three-dimensional data using the software In Vesalius 3 (Centro de
Tecnologia da Informa\selectlanguage{ngerman}ção Renato Archer {[}CTI{]}, Brazil). Data were
then converted into modeling data using slicing software Flash Print
(Flashforge, Japan) and imported into Adventure 3 (Flashforge, Japan).
All the models were made from a polylactic acid filament.

\textbf{Results}

\emph{Case One}

Diagnosis: Squamous cell carcinoma of the external auditory canal
(Pittsburgh classification T1)

Operative method: Lateral temporal bone resection

This is a case of case of a 68-year-old man who originally had a habit
of cleaning his ears with a cotton swab. He visited the hospital with
complaint of left ear pain and was diagnosed with squamous cell
carcinoma by biopsy. The tumor was an ulcerative lesion from the
posterior to the inferior wall of the left external auditory canal
(Figure 1A). Bone destruction was not observed, and the diagnosis was T1
based on the Pittsburg classification (Figure 1B). The distance from the
medial side of the tumor to the tympanic membrane was approximately 3
mm, preservation of the tympanic membrane was impossible, and the
surgical policy was lateral temporal bone resection.

The temporal bone of the patient was reproduced using a
three-dimensional printer preoperatively. The point of reproduction was
that we created the model after having completely performed
mastoidectomy. In other words, we could identify the line of the middle
cranial fossa, sigmoid sinus, posterior wall of the external auditory
canal, and the depth of the lateral and posterior semicircular canals.
The digastric ridge was also clearly reproduced in this model, and the
facial nerve line between the anterior portion of the digastric ridge
and lateral semicircular canals was confirmed (Figure 1C). In addition,
the excision line that progressed from the superior and inferior walls
to the anterior wall of the external acoustic canal was able to proceed
according to the preoperative simulation (Figure 1D).

\emph{Case Two}

Diagnosis: Squamous cell carcinoma of the external auditory canal
(Pittsburgh classification T3)

Operative method: Subtotal temporal bone resection

This is a case of a 52-year-old woman who visited the hospital with
complaint of left otorrhea. A tumor in the left external auditory canal
was observed and biopsied, resulting in a diagnosis of squamous cell
carcinoma.

The tumor had progressed to the mastoid and tympanic cavity and was
diagnosed with Pittsburgh classification T3. In this case, we decided to
perform a lateral temporal bone resection once. However, the tumor was
protruding in the mastoid and the tympanic cavity; therefore, it was
considered that lateral temporal bone resection could not be performed
without cutting into the tumor (Figure 2A). Hence, we decided to perform
subtotal temporal bone resection together with neurosurgeons using the
middle cranial fossa approach. In this case, a full-scale model was
created using a three-dimensional printer before surgery. Since the
surgery utilized the middle cranial fossa approach, unlike that in case
1, we created a model that did not require mastoidectomy (Figure 2B). In
addition, the model was colored to indicate the lines of the sigmoid and
internal carotid arteries (Figure 2C and D). Preoperatively, we
consulted with the neurosurgeons to confirm the excision line (indicated
by black line). Because it was an anatomically unfamiliar approach for
otolaryngologists, the discussion was very useful for preoperative
simulation. Finally, the tumor could be resected margin-free.

\emph{Case Three}

Diagnosis: Right cholesteatoma (Pars flaccida type, Stage II)

Operative method: Tympanoplasty type 0 with mastoidectomy (canal wall
down)

A 72-year-old man presented with complaints of right otorrhea and was
diagnosed with right cholesteatoma and otorrhea. Preoperative CT
revealed a cholesteatoma extending from the attic to the mastoid.
Destruction of the malleus and incus was observed, but cholesteatoma did
not extend around the stapes (Figure 3A); however, tympanoplasty type 0
and mastoidectomy (canal wall down) were adopted.

We reproduced a temporal bone model after the mastoidectomy. Because of
the canal wall down mastoidectomy, the posterior wall of the external
auditory canal was drilled, and the facial ridge was made, as low as
possible (Figure 3B). The risk of facial nerve damage was reduced by
confirming the facial ridge line before surgery. In this case, the
sigmoid sinus protruded into the mastoid, and the jugular bulb was at a
relatively high position. Although the cholesteatoma had advanced deeply
into the sinodural angle, preoperative simulation confirmed the lines of
the middle cranial fossa and sigmoid sinus, making it possible to remove
the cholesteatoma without damaging the vital organs.

\emph{Case Four}

Diagnosis: Left cholesteatoma (Pars flaccida type, Stage II)

Operative method: Tympanoplasty type III with mastoidectomy (canal wall
down)

A 37-year-old man presented with left otorrhea and was diagnosed with
stage II left pars flaccida-type cholesteatoma. Preoperative CT images
revealed a cholesteatoma extending from the attic to the mastoid and
supratubal recess (Figure 4A). Additionally, in the sagittal CT view,
the middle fossa plate was lower towards the anterior; therefore, it is
important to secure the anterior visual field during surgery. First, we
reproduced the temporal bone model after a canal wall up mastoidectomy
(Figure 4B). The posterior wall of the external auditory canal, sigmoid
sinus, crest of the digastric ridge, sigmoid sinus, and line of the
facial nerve were confirmed. However, the anterior line of the middle
fossa plate and supratubal recess could not be confirmed; therefore, it
was considered insufficient for surgical simulation. Thus, we removed
the posterior wall of the external auditory canal and created a
full-scale model after the canal wall down mastoidectomy was performed
(Figure 4C). We simulated the line of the middle cranial fossa
preoperatively and removed the cholesteatoma that had extended into the
supratubal recess without damaging the middle fossa dura.

\textbf{Discussion}

Malignant tumors occurring in the temporal bone are rare with 1.3 per 1
million individuals affected, and are said to be approximately 0.2\% of
all head and neck cancers\textsuperscript{5}. Among cancers, external
auditory canal cancers are the most common, and fewer cancers develop
from the middle ear and ceruminous gland\textsuperscript{6}. Squamous
cell carcinoma was the most common histologic type in 39\% of cases,
followed by basal cell carcinoma in 14\%, and adenoid cystic carcinoma
in 7\%\textsuperscript{7}.

Treatment of external auditory canal cancer includes surgery,
radiotherapy, and chemotherapy, as well as common cancer therapy, and
requires combined modality therapy\textsuperscript{8-10}. For the
surgical treatment of external auditory canal cancer, temporal bone
segmental resection, lateral temporal bone resection, and subtotal
temporal bone resection are cited\textsuperscript{11}. These surgeries
are technically similar to otology surgery, and the degree of difficulty
is high; however, they are often performed in authorized cancer
institutions. With regard to head and neck surgeons, anatomical
knowledge of temporal bone surgery is required; however, there are few
temporal bone surgeons in cancer therapy institutions. Based on these
findings, we believe that a safe surgical strategy for external auditory
canal cancer is necessary.

Recently, several reports of surgical simulation using three-dimensional
printers have been available\textsuperscript{12} in temporal bone
surgeries\textsuperscript{13}. Additionally, it is useful not only in
the simulation of surgery but also in surgery
education\textsuperscript{14}. In our department, practice courses using
actual temporal bones are sometimes held, but the opportunities are
limited. In surgical education, drilling the original model using a
three-dimensional printer is important\textsuperscript{15}, but there is
a difference in drilling simulated bone from real temporal bone.

In 2016, additional surgical support was calculated for temporal bone
tumors based on the size of the original solid organ model for tumor
resection in Japan. In our department, preoperative simulations using a
three-dimensional printer for temporal bone tumors, such as external
acoustic canal cancer, were performed in almost all cases.

When performing lateral temporal bone resection in cases with Pittsburgh
classification T1 or T2, as in case one, mastoidectomy should be
performed initially; however, mastoidectomy should be performed, as much
as possible to secure the anterior field of view of the external
acoustic canal. Preoperative simulations are advantageous because few
surgeons have trained in ear surgeries at cancer specialty facilities.
Case two had a Pittsburgh classification of T3 because the cancer
invaded the mastoid and infiltrated the middle ear cavity. In previous
reports, T3 cases had worse prognosis than T1 or T2
cases\textsuperscript{16} \textsuperscript{17} and were indicated for
subtotal temporal bone resection, which may cause postoperative cranial
nerve palsy \textsuperscript{7}. Moreover, postoperative margin-positive
cases have a worse prognosis than negative cases \textsuperscript{18}.
In such cases, securing a tumor-free surgical margin is challenging. In
cases where the tumor slightly extends to the tympanic cavity or
protrudes into the anterior parotid gland or temporomandibular joint,
tumor-free surgical margins may be obtained through lateral temporal
bone resection. In case two, it was impossible to create a tumor-free
surgical margin through lateral temporal bone resection, and subtotal
temporal bone resection was performed using the middle cranial fossa
approach. The full-scale model created before the operation was
meaningful in sharing the image of the operation with the neurosurgeon.

For otology surgeries, such as tympanoplasty and mastoidectomy, we
created the models preoperatively. Several patients with otitis media or
cholesteatoma have poor mastoid pneumatization, and mastoidectomy is
difficult to perform in these patients. Furthermore, in cases such as
case three, in which the sigmoid sinus protrudes to the mastoid cavity,
surgeons are hesitant to perform posterior excision, and the surgical
field becomes restricted, making it difficult to perform
superior-quality surgery. The simulation was satisfactory in showing and
visualizing the excision limit before surgery in such cases. Moreover,
when performing canal wall up mastoidectomy, the posterior wall of the
external auditory canal was as thin as possible. During the canal wall
down mastoidectomy, the posterior wall of the external acoustic canal
was drilled, and the facial ridge was created, as low as possible. In
this study, we created simple and inexpensive models; therefore, we
could not reproduce the auditory ossicles. However, the use of
three-dimensional printers for ossicular chain reconstruction has also
been reported\textsuperscript{19}. Additionally, by creating full-scale
models made from the material to be drilled, we can expect
higher-quality preoperative simulations\textsuperscript{14}.

Creating full-scale models that are useful preoperatively is beneficial.
Additionally, it was considered useful to share preoperative images with
other doctors using the created full-scale models and to educate young
doctors and medical students during surgery.

\textbf{Conclusion}

Cases of middle ear and temporal bone surgeries using a
three-dimensional printer were examined. The risk of complications could
be reduced by knowing the range limit of drilling and the position of
the vital organ. Moreover, simulations using models are thought to be
useful for the education of young doctors and medical students.

\textbf{Acknowledgements}

The authors thank Y. Higuchi, MD, PhD, for his advice on this article
from the viewpoint of a neurosurgeon.

\textbf{Conflict of Interest}

The authors have no conflicts of interest to declare.

\textbf{References}

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14. Chauvelot J, Laurent C, Le Coz G, et al. 2020. Morphological
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15. Hochman JB, Rhodes C, Wong D, Kraut J, Pisa J, Unger B. 2015.
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\textbf{Figure Legends}

Figure 1

(A) An ulcerative lesion was observed from the posterior wall to the
inferior wall of the left external auditory canal. (B) No obvious tumor
was found on computed tomography (CT), and no bone destruction was
observed. The dotted line is the resection line in CT axial scan. (C) We
determined the depth of the antrum, lateral semicircular canals, middle
cranial plate line, sigmoid sinus, digastric ridge, and facial nerve
line. (D) The glenoid fossa of the mandible can be observed.
Furthermore, the resection line can clearly be seen when we resect
forward after performing mastoidectomy.

Figure 2

(A) Case two was diagnosed with Pittsburgh classification T3 because the
tumor invaded into the mastoid and tympanic cavities. (B--D) Because it
was planned to perform a subtotal temporal bone resection through the
middle cranial fossa, the model was created in which mastoidectomy was
not performed, unlike that in case one. The model was painted blue for
the sigmoid sinus line and red for the internal carotid artery line. The
resection line is shown as the black line.

Figure 3

(A) In case three, tympanoplasty type 0 and canal wall down
mastoidectomy were performed for right flaccid-type cholesteatoma,
extending from the attic to the mastoid cavity. (B) A full-scale model
was created for the mastoidectomy. The facial ridge was created, as low
as possible because canal wall down mastoidectomy would be performed.
Additionally, the lines of the sinodural angle and protruding sigmoid
sinus can be observed in this model.

Figure 4

(A) In case four, tympanoplasty type III and canal wall down
mastoidectomy were performed for left flaccid-type cholesteatoma. The
computed tomography sagittal view showed that the middle fossa plate was
lower towards the anterior, and the cholesteatoma extended to the
mastoid and supratubal recess from the attic. (B) A full-scale model
that was performed the canal wall up mastoidectomy was created. We
confirmed the line of the sigmoid sinus, posterior wall of the external
acoustic canal, digastric ridge, facial nerve, and lateral semicircular
canal. (C) We created the model that was used to performed the canal
wall down mastoidectomy. We confirmed that the anterior of the middle
fossa plate was lower.

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