(1) Médico Residente. Servicio de Cirugía Oral y Maxilofacial (Jefe de Servicio: Dr. Francisco J. Díaz González)
(2) Médico Adjunto. Servicio de Cirugía Oral y Maxilofacial
(3) Médico Residente. Servicio de Anatomía Patológica (Jefe de Servicio: Dr. Agustín Acevedo). 
Hospital Universitario de La Princesa. Madrid

Address:
Dra. Ana Capote
C/ Ginzo de Limia 4, 6º 4,
28029 Madrid, España.
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E-mail: anacapote@inicia.es

Jacob´s disease is a rare condition in which a new joint formation is established between an enlarged mandibular coronoid process and the zygomatic arch. Hyperplasia of the coronoid process was first described by Langenbeck (1) in 1853, although the joint formation between this bone and the zygoma was defined later by Jacob (2) in 1899. Since then, sporadic case reports have been described by the literature.

This entity is most frequent in young patients, with a mean age of 27 (range 16 to 62) (3,4). However, this pathology shows a men dominance (3-5). It can be unilateral with a predilection for the left side (5), although there are some cases of bilateral involvement in the literature (4). The most common clinical presentation is a progressive limitation on mouth opening, so it is often misdiagnosed and treated as a temporomandibular joint (TMJ) dysfunction (4-6).

The pathogenesis of this disease is still not clear although numerous factors have been suggested. It has been proposed that hyperactivity of the temporalis muscle may be an important factor in this condition (5-8). Isberg et al (7) supported the association between Jacob’s disease and internal derangement of the TMJ, as a cause of reactive coronoid process enlargement.

The surgical treatment recommended is coronoidectomy by intraoral approach, such as it has been described by different authors (4,9,10). This treatment avoids external scars and diminishes the risk of facial nerve lesion. However, extraoral approach is still an option in some patients (6,11,12). This second technique is indicated for cases with bilateral coronoid involvement or with concomitant TMJ syndrome that required surgical approach.

We present a new case of Jacob’s disease treated by intraoral coronoidectomy and a TMJ arthroscopy, that was inicially diagnosed as articular dysfunction.

CASE REPORT

A 23-year-old-woman was referred to our Department with a history of 6-years pain on the left temporomandibular joint, increased in the last months and with progressive limitation of mouth opening. The medical history reported a mandibular trauma at 2-years age treated with soft food and rest. No jaw fracture was observed at this time. She had also noticed a long term left zygomatic assymetry.

In the physical examination, the interincisal opening was 30 mm with left laterodeviation in open mouth and 3 mm of protrusive movement, 2 mm of right lateral movement and 6 mm of left lateral movement. She complained pain in the left TMJ on palpation. Bilateral clicking was observed in mouth opening. A left zygomatic body asymmetry was also noticed. This bone was prominent but no mass or swelling was observed.

The initial diagnosis of this patient was temporomandibular joint dysfunction. A X-ray study was requested and the patient underwent conservative treatment with splint therapy. No improvement of the painful symptoms were observed after six months. At this moment, the panoramic radiography showed an elongated left coronoid process (Fig 1). A 3D computed tomography (CT) scan was then developed in which the enlargement of the coronoid was confirmed. There was also an impingement in the inner aspect of the homolateral zygomatic body, signs of bone remodelling, with contact between them during mouth opening (Fig 2).

According to this radiographical findings, hyperplasia of the coronoid process of the mandible was suspected in association with TMJ dysfunction. The patient underwent surgical intervention with general aenesthesia to perform coronoidectomy by intraoral approach. A joint-like formation was found between an enlarged coronoid process and the inner aspect of the zygomatic body. A coronoid osteotomy was performed as well as a smoothing of the zygoma. The resected coronoid process showed a 0,5 mm nodular formation in the articular surface (Fig 3). Additionally, a left TMJ arthoscopy was carried out, in which a moderate disk displacement was found. The patient was treated by lysis-lavage and sodium hyaluronate injection. The postoperative period showed no complications. This surgery was complemented with a physical therapy program during three months.

In the 12 months follow-up period after surgery, the patient presented an interincisal opening of 40 mm with minimal left laterodeviation, normal jaw function and without pain.

Histopathological examination of the surgical sample revealed a nodular lesion made up of mature bone with thickened anastomosing bony trabeculae and narrowed or colapsed intertrabecular spaces filled with fatty marrow. The cortex of the lesion was continous with the cortex of the underlying bone and the outer surface showed an intermitent layer of fibrous cartilage (Fig 4). According to these findings, it was diagnosed as a cartilage-capped exostoses.

DISCUSSION

Symptomatic enlargement of the coronoid process is a rare condition. Although there are not enough epidemiological data of this disease, it can be assumed that asymptomatic cases are more frequent than symptomatic (4,6). However, Jacob’s disease includes only those cases in which an elongated coronoid process forms a synovial joint with the inner aspect of the zygoma (4-6,9). For that reason, this entity is much more uncommon and frequently is unsuspected and misdiagnosed.

Several causes have been suggested for coronoid process hyperplasia. Some authors have proposed that temporalis muscle hyperactivity may play an important role in the reactive enlargement of the coronoid process, as the continuous pull of the muscle provides local blood supply favoring degenerative changes and calcium deposition with calcification of soft tissues (5-8). The compression of the coronoid against the zygoma induces resorption and remodeling of its inner surface, forming a cartilaginous capped pseudo-joint between them. Isberg et al (7) related the hyperplasia with long standing chronic TMJ disk displacement, as a possible etiological factor. In our case, this TMJ dysfunction may be the main factor involved in the hyperplasia of the coronoid process. Trauma, genetic inherence or endocrine stimulus, have also been proposed by several authors (3,13-15).

Progressive limitation in mouth opening is a common clinical symptom of coronoid process impingement, frequently associated with deviation toward the affected side. However, this functional disturbances can be produced by a coronoid hyperplasia or by a chronic disk displacement in the homolateral TMJ. Pain has been considered as infrequent in Jacob’s disease (12,14). It can be due to a concomitant TMJ disease as it was presented in our case. Slight asymmetry in the zygomatic area can be noted in patients with unilateral involvement (4,9). Initial panoramic x-ray films may not show changes in early stages. When the Jacob’s disease or a hyperplasia are suspected, a CT-scan with three-dimensional reconstruction is indicated. This imaging technique is useful not only for confirmation but also for surgical planification (4-6,9).

Two different surgical approaches have beeen described to treat this condition: intraoral and extraoral approach. Intraoral coronoidectomy is the surgical technique prefered for many authors despite the limited mouth opening of these patients (4,9,10). This approach avoids external anaesthetic scars and diminishes the risk of facial nerve lesion (12). Ostrofsky and Lownie (11) use the submandibular approach to execute a coronoidectomy in a case of zygomatico-coronoid ankylosis. This technique provides an adequate surgical field but supports a risk of marginal nerve lesion. For that reason, actually this approach is avoided (12). Coronal approach offers an excellent view of coronoid process with an aesthetic scar under the hair line. This is recommended when the coronoid process is too large to be trapped below the zygomatic arch by intraoral approach in bilateral cases or in cases of concomitant TMJ involvement that required surgical treatment in the same surgery (6,12). Arthroscopic techniques may be a treatment option when associated TMJ disease is present without external surgical incisions, as it was used in the present case.

The postoperative physical therapy should complement surgical treatment to achieve satisfactory and stable long-term results (6,10). Smith (14) presents a case of recurrent coronoid hyperplasia with a regrowth after surgical excision. This could be explained by the formation of a postsurgical haematoma with fibrosis that shows a pathologic calcification. McLoughlin (3) supports this hypothesis in 31 cases of coronoid hyperplasia, as a possible aetiological factor of treatment failure in some patients.

The histological nature of Jacob’s disease leads to confusion. In function of bony and cartilage proportions, the diagnosis can be simple hyperplasia (3,8), osteoma (16), osteochondroma (5,6,9) or cartilage-capped exostoses (15). In the case described, the histopathological study shows a cartilage-capped exostoses as a rare diagnosis in this entity.

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