coronoid process hyperplasia — report of 3 cases...- 311 - 台灣口外誌 coronoid process...

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Taiwan J Oral Maxillofac Surg 台灣口外誌

Introduction

Coronoid process hyperplasia (CPH) is a

rare condition that causes trismus1. No definite

symptoms were noticed, except for decrease in

mouth opening. It was initially described by Von

Langenbeck in 1853 as abnormal elongation of the

coronoid process that cause impingement against

the medial surfaces of zygomatic arches causing

mechanical restriction of mandible during mouth

opening and leads to trismus.1 CPH consists

of histologically normal bone which is different

than Jacob disease which is osteochondroma

arising from coronoid process that may produce

pseudojoint formation between coronoid process

and the zygomatic arch.2

Trismus condition may progressed slowly

and insidiously, it is apparent that some patients

do not find the problem sufficient to seek advice.

Due to its rare condition, CPH can sometimes

be misdiagnosed as temporomandibular joint

problems and patients may have repeated

conservative treatments such as medication or

stabilizing splint. In order to avoid such situation,

we would like report three cases of patients who

visited our department for trismus and diagnosed

with coronoid process hyperplasia. Two of them

were successfully treated with coronoidectomy

and/or coronoidotomy followed by intensive

post-op mouth opening physiotherapy. Etiology,

pathogenesis, diagnostic tools were reviewed to

bring alight of this rare condition.

Case Report

Case 1

Coronoid Process Hyperplasia — Report of 3 Cases

Hani Surianti, Michael Yuanchien Chen

Department of Oral and Maxillofacial Surgery, Taichung China Medical University Hospital,

Taichung, Taiwan, R.O.C.

Abstract

Coronoid process hyperplasia (CPH) is a rare condition that causes trismus. No definite symptoms would be noticed by patients until decrease in mouth opening. We report three cases which received surgical intervention through intraoral coronoidectomy/coronoidotomy followed by postoperative mouth opening physiotherapy within a week after operation. Satisfactory results for the first and second cases, but only mild improvement for the third one. Due to rarity of the condition, the diagnosis of CPH should not be overlooked and be included in the list of differential diagnosis when dealing with trismus.

Key words: Coronoid process hyperplasia, Trismus.

Taiwan J Oral Maxillofac Surg26: 310-320, December 2015 台灣口外誌

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台灣口外誌 Coronoid Process Hyperplasia―Report of 3 Cases

This is a 25 year old male who complained

of pain at bilateral temporomandibular joints

with trismus for 10 years. He denied any medical

history, drug/food allergy, nor trauma history.

Physical examination showed no facial asymmetry,

maximum intercuspation distance (MIO) of

28 mm with strong endfeel resistance (Fig

1A). Tenderness during palpation at the right

preauricular area especially during wide opening.

Limited protrusion (4 mm) and lateral jaw

excursion (R’t 7 mm, L’t 6 mm) also observed

(Fig 1 B,C,D). Panoramic radiograph showed

hypertrophy of bilateral coronoid processes with

its length almost reaching above superior border

of zygomatic arch (Fig 2A). Sagittal section of

the computed tomography scan also confirmed

the above findings (Fig 2 B,C). Due to patient’

s symptoms which suspects temporomandibular

joint problems, we also arranged bilateral

temporomandibular joint MRI. No ankylosis of

the bilateral temporomandibular joints were

noticed. Therefore he was arranged admission

and operation under general anesthesia.

Intraoral approach by buccal vestibular

incision along the anterior border of ramus was

used, and the ascending ramus of mandible was

exposed to the sigmoid notch. The temporalis

muscle was then detached from the coronoid

process with dissector, and an oblique bone

marking was made with reciprocating saw on

buccal cortex from the sigmoid notch to the

anterior border of the ascending ramus. Cut

the coronoid process with fissure bur, slowly

detach the bone from the surrounding muscles.

The entire right side coronoid process was

successfully removed by bone holding forcep.

Passive mouth opening immediately reached

up to 32 mm. The left side coronoid process

was approached with the same procedures and

osteotomized with the tip pulled upward by the

temporalis muscle (Fig. 3) to allow MIO going up

to 48 mm.

Extensive mouth opening exercise started

a week after operation and lasted for a month.

Maximum intercuspat ion d istance (MIO)

maintained above 40 mm which is significant

improvement compared what it was pre-

operatively.

The surg ica l spec imen o f the r i gh t

coronoid process showed normal bone (Fig 4A).

Microscopically, it is composed of dense cortical

bone with lamellar pattern. The cortical bone is

sclerotic and relatively avascular. The medullary

bone is denser than normal with reduced marrow

spaces (Fig. 4B).

Case 2

This is a 13 year old male who complained

of mouth opening limitation progressively since

previous episode of blunt impact to his left

face when he’s playing basketball five years

ago. Maximum intercuspation distance (MIO)

is only 18 mm. Protrusive movement is limited

to 1 mm, lateral excursion to right limited to 1

mm, left is 5 mm. Panoramic radiograph showed

normal contour of bilateral condyle heads but

abnormally hypertrophic coronoid process. 3D

reconstructed facial bone computed tomography

showed bulkiness of bilateral coronoid process

with impingement to the medial aspect of the

zygoma (Fig. 5 A,B). Under the diagnosis of

bilateral coronoid process hyperplasia, bilateral

coronoidectomy was successfully done. Patient

started mouth opening physiotherapy on the

5th day after operation, and maintained good

maximum intercuspation distance (MIO) of 37

mm. Pathology report of the specimen also

showed normal bone (Fig. 5 C,D).

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Case 3

This is a 28 year old female who also

compla ined o f mouth opening l imi tat ion

progressively since junior high school. Square

face with strong muscle tone of bilateral masseter

muscles were noticed (Fig. 6A). Initial maximum

intercuspation distance (MIO) is 22 mm (Fig.

6B). Panoramic radiograph confirmed the

hypertrophic coronoid process (Fig. 7A). Right

side coronoidectomy and left side coronoidotomy

through intraoral approach was done (Fig. 7B)

which immediately led to increase of MIO up to

45 mm. Specimen obtained showed abnormally

bulky contour (Fig. 8) and microscopically

it revealed the same findings as the first and

second patient. After post-operative mouth

physiotherapy for two months, MIO reaches 30

mm, which is slight disappointing than what we’

ve expected.

Discussion

Epidemiology

Prevalence statistics of CPH varies. In

one earlier literature, 8 out of 163 patients

with limitation of mouth opening was caused by

elongation of coronoid process which accounts for

an incidence rate of 5%3. Panoramic radiographs

for randomly selected sample of 2000 patients

came up with prevalence rate of 0.05%.4 Recent

literatures emphasized that average interval

from disease onset to diagnosis is about 7 years,

while mean age of occurrence is 14 years old.

The bilateral CPH are reported 4.1 times more

frequently than the unilateral form. Most CPH

patients are male (male to female ratio is 3.3:1).

Unilateral form is slightly more frequent in

women, the bilateral form more frequent in men.5

In unilateral cases, facial asymmetry, mobile lump

above the zygomatic arch, opening deviation to

affected side, facial pain may occasionally happen. 6

Etiology

Etiology and pathogenesis of CPH are

controversial. CPH have been referred to

anomalies of shape and growth of coronoid

process alone, however improved imaging

technology have led to observation of association

of anomaly in coronoid apophysis with alteration

in malar bone. Trauma, endocrine stimulus,

genetic inheritance, familial occurrence have

all been proposed6 to influence the surrounding

muscular and skeletal structures. Syndromic

relationship exists in trismus-pseudocamptodactyl

syndrome6, 7 which cause shortened muscle

tendon units and Moebus syndrome5 which

causes facial paralysis at birth. There are many

literatures which support the temporalis muscle

hyperactivity theory1. Thick fibrous bands were

palpated at insertion of temporalis muscle5,

amianthoid fibers in temporalis muscle has

even been identified by electron microscopy6.

However, there are literature which contradicts

the muscle hyperactivity theory are the results of

electromyography (EMG) of both temporalis and

masseter muscles1 which showed normal activity

of those muscles. Therefore there are still many

controversies regarding the muscle hyperactivity

theory.

Mandibular hypomobil ity may also be

suggested that cause secondary CPH.8 Gradual

reduction of masticatory efficiency increases the

functional demand on the structures to maintain

optimal function, both in forced opening as well

as in clenching or grinding of the food. Reduced

muscle activity leads to chronic hyperemia

and fatigue thus triggering off an inflammatory

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Fig. 1. (A) Mouth opening difficulty was noted with maximum intercuspation distance is 28 mm from

upper left to lower left central incisor. (B) Protrusive movement is about 4 mm. (C) Lateral

excursion to the left is about 6 mm. (D) Lateral excursion to the right is 7 mm.

Fig. 2. (A)(B)(C)Hypertrophy of the coronoid process with elongation beyond the zygomatic arch.

AB

C

D

A

B C

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Fig. 3. Post-op panoramic radiograph showed the bone cut of the right coronoid process and the gap

coronoidotomy at the left coronoid process. Left coronoid process upward displacement was

seen due to pull of the temporalis muscle (as arrowheads). Bilateral condylar head are still within

the glenoid fossa.

Fig. 4. (A) The surgical specimen obtained of the hypertrophic coronoid process. (B) Microscopically

(hematoxylin & eosin original magnification x100), it is composed of dense cortical bone with

lamellar pattern.

BA

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Fig. 5. (A, B) 3D reconstructed image of the second patient showed bulkiness of bilateral coronoid

process with impingement to the medial wall of the zygoma. (C) The surgical specimen obtained

from the second patient showed enlargement of bilateral coronoid process. (D) Microscopically

(hematoxylin & eosin, original magnification x100) specimen also showed mature bone formation.

Fig. 6. (A) Square face with strong appearance of the bilateral masseter muscles were seen. (B)

Maximum intercuspal distance of this patient is 22 mm.

B

B A

C D

A B

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Fig. 7. (A) Pre-operative panoramic radiograph hypertrophic of bilateral coronoid process with its

length above the zygomatic arch. (B) Post-operative panoramic radiograph showed right side

coronoidectomy and left side coronoidotomy. Similar to the first patient, the left side coronoid

process is pulled upward by the temporalis muscle.

Fig. 8. The hook shape at lateral surface of the right coronoid process.

A

B

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response, excess of growth factors and cytokines

may later contribute to permanent fibrotic tissue

and persistent shortening and contracting of

muscle fibers “physiopathologic distraction

osteogenesis” of coronoid process. When

coronoid process contacts the medial surface

of zygomatic arch, it leads to mechanically

restricted mouth opening9.

Association of square-shaped mandible

(SQM) and coronoid process hyperplasia (CPH)

have also been published10. Bone deposition

occurring in the area of deposition occurring

in the area of insertion of masseter muscle due

to hyperactivity which led to appearance of

SQM, such as our case III. Etiology is similar

to temporal hyperactivity theory because the

masticatory muscles are closely related. However,

no conclusive evidence affirming the situation

were found.

Diagnostic Tools

D i agnos i s o f CPH can be ob ta i ned

through radiographic image and careful clinical

examination. By using Levandoski panographic

analysis, a maxillary vertical midline was made

and perpendicular line when it crosses the lower

border of mandible (Go’), the tip of condyle

(Go’), tip of condyle (Cd’). When Kr’-Go’:

Cd’-Go’ ratio is greater than 1.1, diagnosis

supports CPH11. In our cases, al l of the

measurements except for the right side of the

first patient are greater than 1.1, therefore all

compatible with the diagnosis of CPH (Table 1).

Water’s view for viewing the relationship

between coronoid process and its relation to

the zygoma has also been mentioned. Lateral

cephalographs have also been used, however

the disadvantage is that the images of bilateral

coronoid processes overlay each other and

precise determination of landmarks are not

feasible12.

C o m p u t e d t o m o g r a p h y w i t h 3 D

reconstruction is the gold standard. An auxiliary

line was drawn through the deepest of sigmoid

notch. Length of coronoid and condyle process

are measured. Normal coronoid/condyle ratio at

CT- based analysis showed a value of 0.7812. In

our case, the measurements are all above 0.78,

which is also compatible with the diagnosis of

CPH (Table 2).

Magnetic resonance imaging (MRI) is

not good for bone abnormalities, but can be a

diagnostic tool when diagnosing concomitant

temporomandibular joint (TMJ) disc disorders13.

Treatment Modalities

Due to pathogenesis of CPH is caused by

mechanical restriction that leads to functional

alteration, surgical resection is the only way. Two

types of surgery are performed: coronoidectomy

and coronoidotomy.

Table 1. Measurements of Kr’-Go’: Cd’-Go’

ratio in our patients using Levandoski

panographic analysis

Right side Left side

Case I 1.09 1.12

Case II 1.11 1.17

Case III 1.146 1.12

Table 2. Measurements of ratio between length

of coronoid and condyle process in CT-

based analysis

Right side Left side

Case I 0.88 1.257

Case II 1.388 1.97

Case III 1.007 1.06

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Coronoidectomy can be done through

extraoral or intraoral approaches. The extraoral

approaches such as bi-coronal/face lift, hemi-

coronal, submandibular has been published It is

preferred during such conditions: (1) size, bulbous

shape, position of coronoid process, which can

be determined from CT scan, (2) concomitant

involvement of TMJ, (3) occurs bilaterally, (4) in

need of zygomatic removal/reconstruction.14

Co rono i d ec t omy t h r ough i n t r a o r a l

approaches is preferred in our case so that no

skin incision wounds and no danger to facial nerve

function. Potential complication of herniation

of buccal fat pad12 did not happen in our cases.

To secure, the coronoid process, we drilled a

hole and inserted stainless steel wire to pull the

detached coronoid process, although there are

other ways such as using titanium mini screw10

or forceps to secure the process. Advantages of

coronoidectomy are: (1) mechanical obstruction

is removed; (2) histology can be obtained;

however disadvantages includes: (1) detachment

of temporalis muscle blindly therefore is difficult

and traumatic procedure; (2) post-op hematoma

and subsequent fibrosis may cause relapse6.

Coronoidotomy supposedly leads to less

trauma, less postoperative morbidity and better

results1. Disadvantages are risk of reattachment

of the process, mild disocclusion caused by

coronoid process interfering with the upper

part of the ramus upon mouth closing15. The

gap during coronoidotomy of first and third

patient fortunately is wide enough not to cause

disocclusion.

Postoperative mouth opening physiotherapy

( s t retch ing exerc ises ) are essent ia l for

preservation of the increased mouth opening. All

of our cases start the exercise at postoperative

a week. However, different duration, compliance

to pain makes the comparison between patients

impossible. Normal mouth opening is achieved

within a month by the first and second patient,

however limited improvement is noted at the

third patient. Therefore, it is believed that

besides hyperplasia of the coronoid process,

hypertoniticity of the masseter muscles, strong

mandibular angles that conclude to the square-

shaped mandible (SQM) may lead to relapse. MIO

of the third patient still reaches 30 mm, which

the patient felt satisfactory but was considered

less than what we expected.

All of the histopathology of our patients

consists of normal bone, therefore is distinguished

from Jacob disease which is osteochondroma with

regions of endochondral ossification enclosed

by hyaline cartilage13. Relapse of the CPH after

surgery is caused by regeneration of coronoid

process from the top which may eventually unite

with the ramus and cause limitation of mouth

opening again16. Therefore, long term follow up is

mandatory.

Conclusion

The bone overgrowth of CPH can be a

compensatory hyperplasia rather than a direct

effect of disease process. Knowledge of its

existence could preserve patient from months of

discomfort. Whether the surgical intervention

i s per formed v ia extraora l or intraora l ,

coronoidectomy or coronoidotomy, patient’

s compliance for postoperative mouth opening

physiotherapy is the most important contributor

to success.

Reference

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Received: August 05, 2015Accepted: November 28, 2015Reprint requests to: Dr. Michael Yuanchien Chen, Department of Oral and Maxillofacial Surgery,

Taichung China Medical University Hospital, No.2, Yu-der Rd., Taichung, Taiwan, R.O.C.

雙側喙狀突增生—三例病例報告

簡杏宜　陳遠謙

中國醫學大學附設醫院口腔顎面外科

摘　　要

下顎骨喙狀突增生是一個罕見疾病，臨床表現為漸進性的張口受限。本篇

描述三位在本院接受手術治療的案例。第一位和第三位患者接受右側喙狀突

切除術、左側喙狀突切開術。第二位患者接受雙側喙狀突切除術。三位患者

於術後一週開始張口復健。第一和第二位患者術後張口度明顯改善，第三位

患者則是效果有限。本篇主要目的是整理從檢查至診斷提醒臨床醫師，面對

張口受限的病人，下顎骨喙狀突增生應列入重要的鑑別診斷之一。

關鍵詞：喙狀突增生，張口受限。

coronoid process hyperplasia — report of 3 cases...- 311 - 台灣口外誌 coronoid process...

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