Portuguese Version

Year:  2003  Vol. 69   Ed. 3 - (17º)

Relato de Caso

Pages: 406 to 413

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Foramen of Huschke and its clinical implications

Author(s): Camilo A. Melgaço[1],
Letícia M. Penna[2],
Paulo I. Seraidarian[3]

Keywords: foramen of Huschke, incidence, clinical implications.

Abstract:
During temporal bone development and formation it is noted the presence of a foramen in the medial portion of the external auditory canal (foramen of Huschke). This foramen is normally present until the age of 4 or 5 years old, but in some people it persists throughout life. The persistence of this foramen and its clinical implications related to the temporomandibular joint, ear and nearby structures has been reported by many authors. Therefore, it is important that dentists, otorhinolaryngologists, speech pathologist and physiotherapists have a wide knowledge about the consequences of the presence and persistence of the foramen of Huschke.

INTRODUCTION

The foramen of Huschke is present in the early stages of development and formation of the tympanic portion of the temporal bone. Its location is the central part of the tympanic plaque (posterior wall of the articular fossa or anterior wall of the external auditory canal). The presence of this foramen is a frequent finding in children up to the age of 5 years, being of varied sizes and shapes. However, many literature reports showed that the foramen can persist in adults, characterizing an anatomical anomaly. The foramen was named after the otorhinolaryngologists S. Huschke, who described it in 18321-5. The purpose of the present article was to review the literature concerning the embryology, incidence and clinical implications of the presence and persistence of foramen of Huschke.

EMBRYOLOGY

The temporomandibular joint (TMJ) is formed by two bone components that are the temporal bone (skull base) and the mandibular condyle 6.

The temporal bone develops by the fusion of three parts that can be separated one from the other at birth. The parts are the petrous region of the temporal bone (endochondral origin), tympanic bone (membranous origin) and temporal squamous portion (membranous origin). The styloid process is included only later 7.

On the fourth week of intrauterine life there is the presence of branchial arches, grooves and branchial fissures and pharyngeal pouches. The first pharyngeal pouch will form the auditory tube and the tympanic cavity, whereas the first branchial fissure will originate the external acoustic canal. The auricular pinna develops from the first branchial groove and it is derived from the mandibular and hyoid arch tissues. The tympanic membrane is formed from the first branchial membrane that is located between the first pharyngeal pouch and the first branchial groove 1, 8.

Close to the 9th intrauterine week of life, four small ossification centers arise close to the tympanic membrane. During the 10th week, those centers get together and form the tympanic ring that is interrupted in its upper portion by the Rivinus notch, characterizing it as U shaped. This tympanic ring keeps on growing to get together with the squamous portion of the temporal bone by the 35th week of intrauterine life. At birth, the tympanic ring has two bone prominences or tubercles in U shape (anterior and posterior tympanic tubercle). During the first year of life, these processes grow towards each other and merge. Concomitantly, the inferior portion of the ring grows laterally to merge with the petrous portion of the temporal bone, increasing the length of the auditory external canal. The merge of the tympanic ring is initially incomplete in its inferior and anterior portion, resulting in an opening (foramen of Huschke) present to the 4th or 5th year of life. This merger separates the external auditory canal superiorly from the foramen of Huschke inferiorly. The position of the foramen changes anterior-inferiorly to anteriorly as a result of growth and development downwards and forwards to the mastoid process. However, this foramen can persist for the whole life. If it happens, the retrodisk region of the temporomandibular joint region and the medial portion of the auditory external canal are separated only by soft tissue 1, 3, 5, 9 (Figure 1-5).

Therefore, foramen of Huschke represents non-ossification of the anterior-inferior portion of the tympanic plaque, which originates from membranous structures 5.

Incidence and Persistence of Foramen of Huschke in Adults

Upon the study of anatomy and embryology of the temporal bone we can detect the presence of a bone defect in the medial wall of the external acoustic canal (posterior wall of the articular fossa). This condition remains up to approximately four years of life. However, in approximately 20% of the adults there may be remains of the defect, which should not be confused with trauma lesions 7.
In a study with 100 human skulls from the Department of Oral Anatomy, University of Illinois, they found 32 foramens greater than 1 mm in diameter in 200 tympanic plaques (16% of the sample). Seven of the 100 skulls observed had bilateral foramens (7%). They were on average 1 to 7 mm in diameter and normally located on the lateral region of the tympanic groove (attachment point of the tympanic membrane), or occupying part of the groove in some cases. Foramen of Huschke was then described as having a cribiform or complete shape. In some cases there was only a transparent opening of the bone on the foramen region 9.

Another study conducted with 377 skulls found an incidence of foramen of Huschke in 27 of them (7.2%). Of the total examined cases, 300 skulls were Chinese and 77 Canadian. The incidence of the foramen was 6.7% and 9.1%, respectively. It was reported that 14 of the 27 skulls presented bilateral foramen and 13 had unilateral foramens. The predominant shape was oval (41 cases), followed by round (15 cases), and irregular (2 cases). The average size of the foramen was 2.7 mm and 3 mm for both longitudinal and transversal measures 10.

Upon observing 776 Brazilian skulls, Faig-Leite & Horta5 reported the presence of foramen of Huschke in 9.93% of the examined skulls (77 skulls). The foramen was unilaterally found in 41 skulls (53.2%) and bilateral in 36 skulls (46.8%). It was statistically confirmed that the higher incidence was in females and in melanoderm subjects more than in leukoderm ones (even though among ethnic groups the difference had not been statistically significant). The foramens found could be classified as rounded (17.7% of the cases), oval (17.7% of the cases) and irregular (64.6% of the cases) and the average transversal size was 2.35 mm and longitudinally, 2.48 mm. The mean distance from the most lateral portion to the external acoustic canal was 10.15 mm (Figures 6-10).

Clinical Implications of the Persistence of Foramen of Huschke

Septic arthritis or arthritis caused by specific infection is characterized by an inflammation of the joints owing to a wide range of infections (generated by gonococcus, streptococcus, staphylococcus, pneumococcus and tuberculosis bacilli) that can produce polyarticular compromise, be it by blood or lymphatic metastases, or direct extension of focal infection. The TMJ seem to be free from such infections, except in gonococcus infections. About 5% of the patients with gonorrhea have gonococcus arthritis and out of them, about 3% have affection of TMJ. The most common form of infectious arthritis of the TMJ is the one caused by direct extension of the infection to adjacent structures such as those of dental origin, otologic, parotid gland, osteomyelitis and other facial infections 12. Systemic affections such as diabetes mellitus, poor nutrition, debilitation or immunosuppression owing to the use of corticosteroids and preexisting articular diseases (such as rheumatoid arthritis) can easily transmit infections (especially by Staphylococcus aureus) to the TMJ, causing septic arthritis 3,13.

Anatomically, there is proximity between the auditory external canal and the TMJ, and the articular capsule is attached to the scamotympanic fissure. Therefore, congenital dehiscence of the cartilaginous canal and Santorini fissure (scamotympanic fissure) or the persistence of the foramen of Huschke can contribute to the diffusion of an infection to the joint 14, 15.

The most common symptoms in TMJ septic arthritis are pain upon mandibular movements, pre-auricular bulging, extensive sensitivity to palpation, and limited range of motion. Most symptoms can be found in isolated otitis media, hindering the precise diagnosis. 13

TMJ septic arthritis has also been concomitantly reported with complications of external otitis, even though it is rarer. In the report of a clinical case, a male individual presented liquid drainage from the right external ear canal and noisy movement upon opening and closing the mandible. The otoscopy showed the presence of a tumefaction on the inferior region of the external auditory canal, covered by greenish secretion (probably causing the external otitis). The tympanic membrane was intact. The closing movement of the mandible was detected by the onset of fluid and air bubbles at the tumefaction site. The treatment was conducted with cleaning of the external acoustic canal, followed by antibiotics and topical corticoids. The examination of the temporal bone of the patient (after his death owing to fecal peritonitis) showed bone defect on the anterior and inferior regions of the auditory canal, communicating the external ear with the articular cavity (foramen of Huschke)3.

The origin of a parotid salivary fistula, even though rare, can occur as a result of the various forms of trauma that lead to parenchymal or gland duct impairment. Such cases require a variety of surgical procedures for its correction. The parotid gland is found in the external portion of the anterior and inferior walls of the external auditory canal, normally in its cartilaginous portion. Some times the gland can reach the articular fossa, through the TMJ. This part is named glenoid lobe and it is in contact with the bone and cartilaginous portions of the auditory canal. The lobe is affected by mandibular movements. In a case report, a patient presented 6-month clinical history of aqueous liquid drainage with clear aspect on the right ear, increasing during the meals. There were no reports of previous traumas, surgeries, fistulae or pathological abnormalities of the parotid. The right tympanic membrane showed no abnormalities and the external auditory canal had a point of tumefaction in its anterior wall. When the patient was instructed to swallow something soft, there was discharge of the liquid at this point. The tests were conducted and it was detected that external otitis had developed (during the 6 months of history) owing to salivary irritation. The presence of salivary fistula in the external auditory canal can be confirmed by the anatomical variation that the parotid gland seems to present, associated with bone defect on the central and anterior regions of the tympanic plaque or posterior wall of the articular fossa (foramen of Huschke)5.

Laurent & Cirrel16 described a tumefaction on the anterior region of the external acoustic canal of an adult patient with history of facial trauma. Upon closing the mouth, they observed partial obstruction of the external acoustic canal. The abnormality was located 10 mm deep. as of the tragus. When the patient was instructed to remain with his mouth opened, an invagination of the tissues was observed at the tumefaction site. There was report of hearing loss and auricular pain. Computed tomography detected the presence of a bone defect of approximately 1 cm2, in the region of the tympanic bone (foramen of Huschke). The proposed surgery was to redefine the correct diameter of the auditory canal based on the graft of lyophilized cartilage, interposed between the retrodiskal tissues of the TMJ and the bone defect.

Spontaneous hernias of TMJ to the inside of the external acoustic canal have also been reported. Such hernias are non-painful and bilateral in many occasions, located 30 mm from the tragus, in the anterior region of the external acoustic canal. In the absence of facial trauma history, lack of closure of foramen of Huschke can be proposed as a possible etiology 14.

In a case report it was observed spontaneous fistula that developed in the anterior wall of the external acoustic canal. The fistula was located 27 mm from the tragus and there was no history of facial trauma. The main complaint of the patient was "discharge of an uncolored liquid through the ear". Mastication increased intensity of the liquid. The hypothesis of a synovial liquid was considered, since sialogram of the parotid, associated with other gland tests, did not reveal any abnormalities. The exam of the liquid revealed that it was not of salivary origin. A bone defect in the tympanic membrane, described as incomplete closure of foramen of Huschke, was detected in the axial computed tomography 17.

Heffez et al.4 reported a clinical case of a patient that presented complaint of pre-auricular pain that increased with mastication and environmental temperature changes. Pain symptoms or limitation of mouth opening were not detected. There was no previous reports of trauma, TMJ or ear surgery, nor signs of infection. Mandibular movements were normal and there was no articular noise. The tympanic membrane did not present abnormalities and a tumefaction on the wall of the anterior external auditory canal could be detected (this tumefaction obstructed the visualization of the tympanic membrane). Whenever the patient was asked to open his mouth widely, the tumefaction retracted, leaving a depression in its place. The computed tomography showed attachment of retrodiskal tissues of the TMJ on the central region of the tympanic plaque, where there was a bone defect of rounded margins (foramen of Huschke). Such defect was located approximately 15 mm from the tympanic membrane. No surgeries were conducted as treatment.

A second clinical case reported by the same authors included history of surgical interventions in both TMJs. The patient related intense pain on the right ear. They detected muscle dysfunctions on both sides of the joints and anterior displacement of the articular disk to the right side. In the otoscopy, they detected a tumefaction of the anterior wall of the external acoustic canal that disappeared when the patient opened his mouth. Computed tomography revealed the presence of defect in the central portion of the tympanic plaque (foramen of Huschke). In both cases, the authors concluded that the pressure of the condyles against the retrodiskal tissues (when the patient maintained his mouth shut), associated with closure of the foramen of Huschke, was enough to justify the reported tumefactions. They still added that the communication could serve as a means of communicating infections from the middle and external ears to the tissues of the TMJ, and vice-versa.

The presence of foramen of Huschke was reported as the probable cause of weakening the bone structures of the external auditory canal, with a possible trend to fracture in cases of traumas 9.

Persistence of the Foramen of Huschke after TMJ Arthroscopy

Arthroscopy is a type of test that was initially used for the diagnosis and treatment of knee problems and other major body joints. The advance of technology enabled arthroscopy to be used also to diagnose TMJ disorders 18.

Since the introduction of TMJ arthroscopic surgery in 1975, much has been said about the anatomical landmarks and the pathologies observed during the procedure. Few studies, however, reported the results and follow up of the series. The procedure seemed to be effective to eliminate the painful symptoms of TMJ and restore the mandibular function in patients without articular disk reduction (even in non-surgical treatment failure). Arthroscopy is not only effective in treating some TMJ disorders, but it is also a useful tool for the diagnosis and investigation of the joint pathologies 19.

TMJ arthroscopy is conducted with rigid optic fibers with diameter that ranges from 1.7 to 2.7 mm 20-23. The exam can show cavities and joint tissues, make diagnosis, irrigation, biopsy, remove intrarticular adhesions, correct traumas located in the lateral capsules (causing movement restrictions in the upper compartment of the TMJ) and also take photos of the region 20, 24.
Arthroscopy has an important role in the surgical evolution of the treatment of TMJ. This technique provides information about the articular surfaces that did not use to be assessed by other methods 21.

The TMJ has a superior and inferior articular compartments separated by the articular disk. Upon inserting the arthroscope into one of the compartments, the operator is guided through bone landmarks of the articulation and the skin, or indirectly through the fiber tip of the device 20.
A liquid solution (solution of Ringer's) is injected to expand the superior space of the TMJ. Thus, the arthroscope coupled to the video camera is inserted in the articular capsule and the joint space is examined 18. Within the limits of the arthroscopy, the anterior wall of the external auditory canal defined a posterior limit with the articular cavity 20.

If on the one side this procedures seems to be a good way to solve problems in which other clinical methods had not reached the expected results, on the other side some complications have been reported resultant from arthroscopy. They are 212, 25, 26:

- hemorrhages;
- sensorial and motor abnormalities;
- damage to the synovial tissue of the joints (causing inflammations and infections);
- persistent pain;
- infections and injury to the middle and internal ears causing hearing loss, vertigo and facial paralysis.

The anterior wall of the tympanic portion of the temporal bone can not be entirely intact, presenting discontinuation in its central part (foramen of Huschke) in which it can be one of the explanations of the vulnerability of the middle and inner ears 1. In such case, the separation between the articular fossa and the external ear is then the soft tissues that can be easily perforated by instruments used in arthroscopy 9.

TMJ arthroscopy is a procedure that can cause perforation of the posterior ligament of the articular disk. The junction between the cartilaginous and the bone portions of the external auditory canal can be easily penetrated by instruments used during the test. For this reason, arthroscopists should be aware of the complications and be careful when inserting the instruments and defining the penetration depth of the instruments 20, 27.

There has been an increase in frequency of complications originated by the use of arthroscopy technique. Such complications can be: 20

- hearing loss caused by infections, traumas to the tympanic membrane originated by the use of the malleus technique;
- rupture of the oval window and problems with the membranous labyrinth (caused by poorly positioned instruments in the middle ear);
- facial paralysis and bone fractures of the external auditory canal.

After the TMJ arthroscopy, Van Sickels et al. 23 reported a case of injury of the middle ear structures and perforation of the tympanic membrane leading to conductive hearing loss. According to the authors, the possible cause of such injuries was the introduction of instruments used in the arthroscopy in the retro-direction, reaching the posterior wall of the articular fossa (anterior part of the tympanic plaque) where there was persistence of foramen of Huschke.

In the exam of three patients with otologic complications of TMJ arthroscopy, they detected tympanic membrane ruptures in the three cases and labyrinthic lesions in two, with complete and profound sensorineural hearing loss. In the third patient, they detected displacement of the incus, conductive hearing loss and facial paralysis owing to lesion to the tympanic segment of the facial nerve, in the area of the oval window. A possible explanation to such complications was the introduction of instruments used during the arthroscopy in the posterior direction. Such instruments cross the posterior wall of the articular fossa (anterior wall of the tympanic plaque) that could have the persistent foramen of Huschke, or a thin bone layer in the region. The instruments, in such cases, penetrated the external acoustic canal immediately in a lateral position to the tympanic ring and membrane, perforating them and causing damage to the structures of the middle and inner ears. Another possible anatomical area to arthroscopy access would be the junction of the bone and cartilaginous portions of the external acoustic canal. The authors added that an irrigation conducted by the arthroscopy positioned in the middle ear could contribute to the pathologies related to the labyrinth 20.

CLOSING REMARKS

Based on the literature review, we concluded that:

- The foramen of Huschke is a structure present in embryology and development of the temporal bone, closing at the age of 5 years;

- In the Brazilian population, this foramen persists in approximately 10% of the adult population;
- The foramen enables communication, separated by soft tissues, between the articular fossa and the external acoustic canal;

- Innumerous clinical implications related to the non-closure of the foramen have been reported in the literature, such as external and middle otitis media, infectious arthritis, hernias and fistulae in the external auditory canal, middle ear and internal lesions with auditory compromise, bone fractures by weakening of the anterior wall of the external acoustic canal, in addition to facial neuromotor damage;

- It is essential that professionals who work with the areas of TMJ and ear pathology be aware of the existence and the clinical implications resultant from the persistence of the foramen of Huschke.

REFERENCES

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1. Dentist, graduated from the School of Dental Sciences, UFMG, undergraduate studies under course, School of Speech and Language Pathology and Audiology, Medical School, UFMG, Instructor of the Updating Course to Dental Office Assistants, UFMG and Instructor of the Training in Dental Office Assistants, CEO-IPSEMG.
2. undergraduate studies under course, School of Speech and Language Pathology and Audiology, Medical School, UFMG
3. Master and Ph.D. in Restoring Dental Spiciness - major in buco-maxillo-facial prosthesis; Coordinator of the Master studies in dental prosthesis, PUC-MG, Professor responsible for the discipline of Occlusion and TMJ, Universidade Ibirapuera-Unib, Assistant Professor, Department of Debtal Prosthesis, School of Dental Sciences, São José dos Campos/UNESP.

Address correspondence to: Camilo Aquino Melgaço - Rua Espírito Santo nº 1111, apto. 1401 Centro Belo Horizonte MG 30160-031 - Tel (55 31) 3226-56-16/ (55 31) 9628-97-51# E-mail: camiloaquino@zipmail.com.br

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