1.題目: Coronoid process hyperplasia: Report of 3 cases
2.簡題: 雙側喙狀突增生-三例病例報告
3.作者姓名: 簡杏宜(最高學位:國立陽明大學學士)
4.服務單位及職位:中國醫學大學附設醫院口腔顎面外科第五年住院醫師
5.稿件負責人:簡杏宜 (Hani Surianti). Tel: 0952629572, .E-mail: madcoppp@gmail.com
ADD:台中市北區美德街 42 號 6 樓之 2
共同作者: 簡杏宜(Hani Surianti
) , 陳遠謙(Michael Yuanchien Chen)
通訊作者: 陳遠謙(Michael Yuanchien Chen).
Department of Oral and Maxillofacial Surgery, Taichung China Medical
University Hospital, No.2, Yu-der Rd., Taichung, Taiwan, R.O.C. e-mail:
mychen@mail.cmuh.org.tw.
機構名稱: 1. Department of Oral and Maxillofacial Surgery China Medical University
Hospital.
2. School of Dentistry, China Medical University.
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.
Keywords: coronoid process hyperplasia, trismus.
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。 關鍵字: 喙狀突增生、張口受限 Introduction
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 I
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 intercuspation distance (MIO) maintained above 40 mm which is significant improvement compared what it was pre-operatively.
The surgical specimen of the right 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 II
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).
Case III
This is a 28 year old female who also complained of mouth opening limitation 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 occurence 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 occassionally 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 proposed 6 to influence the surrounding muscular
and skeletal structures. Syndromic relationship exists in trismus-pseudocamptodactyl syndrome 67 which
cause shortened muscle tendon units and Moebus syndrome 5 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 muscle 5 , amianthoid fibers in temporalis muscle has even been
identified by electron microscopy 6. 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.
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 triggerring off an inflammatory 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 opening
9.
Association of square-shaped mandible (SQM) and coronoid process hyperplasia (CPH) have also been published 10. 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
Diagnosis of CPH can be obtained 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, all 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.
Computed tomography with 3D 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 0.78 12. 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 disorders 13.
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.
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
Coronoidectomy through intraoral 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 screw 10 or forceps to secure the process. Advantages of coronoidectomy are: (1) mechanical obstruction
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 closing 15. The gap during conoidotomy of first
and third patient fortunately is wide enough not to cause disocclusion.
Postoperative mouth opening physiotherapy (stretching exercises) are essential 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 again 16. 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 is performed via extraoral or intraoral, coronoidectomy or coronoidotomy, patient’s compliance for postoperative mouth opening physiotherapy is the most important contributor to success.
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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
