Magnetic resonance imaging around the eustachian tube

Imaging of the Eustachian tube and its function: a systematic review

Introduction

The Eustachian tube is a complex and inaccessible structure, which maintains middle ear ventilation to facilitate transmission of sound from the tympanic membrane to the cochlea. A renewed interest in treatments for eustachian tube dysfunction has led to a demand for methods of imaging the Eustachian tube, and assessing tube opening non-invasively. This review aims to summarise the use of imaging in the anatomical assessment of the Eustachian tube, and to explore how radiological techniques can be used to assess tube function.

Methods

A systematic review of the literature was performed with narrative data analysis.

Results

With high-resolution images, the soft and bony anatomy of the Eustachian tube can be assessed in detail. CT and MRI are best suited to identifying features associated with obstructive or patulous Eustachian tube dysfunction, though true assessments of function have only been achieved with contrast enhanced radiographs and scintigraphy. A single modality has yet to provide a complete assessment. No test has entered routine clinical use, but further development and research is underway.

Conclusion

Significant information can be gained from imaging the Eustachian tube, and as faster acquisition techniques are developed, it is possible that dynamic imaging of tubal opening could play an important role in the assessment of patients with ET dysfunction.

Functional MR imaging of the eustachian tube in patients with clinically proven dysfunction: correlation with lesions detected on MR images

OBJECTIVES

To visualise the function of the Eustachian tube by MRI and assess the effect of surrounding lesions.

METHODS

Using 1.5 T MRI, 32 Eustachian tubes of 16 patients with clinically proven dysfunction (clinical symptoms, such as autophonia and fullness and non-opening at tympanometry) were investigated. For depiction of the anatomy and associated abnormalities, coronal and axial T2-weighted turbo spin echo sequences and a T1-weighted-2D-gradient echo sequences were acquired. Eustachian tube opening was analysed with real time turbo-gradient echo sequences during a Valsalva manoeuvre.

RESULTS

Dysfunction, that is, failure of opening of the Eustachian tube as shown by MRI, correlated in all patients with tympanometry. Lesions detected included nasopharyngeal carcinoma in 4 patients. Mucosal swelling in the paranasal sinus was present in 9 patients. One patient had postoperative defects. In two patients both pharyngotympanic tubes did not open although no structural abnormalities could be depicted.

CONCLUSIONS

The opening of the Eustachian tubes during the Valsalva manoeuvre is assessable on MRI. Failure of opening may be due to swelling of the mucosa and may be also associated with tumours. MRI assessment may be helpful in patients with chronic otitis media, where the information about tubal function is important in preoperative planning.

KEY POINTS

•Eustachian tube opening during Valsalva manoeuvre can be visualised with MRI •Lesions hampering tubal opening can be delineated at the same MRI examination •Functional MRI of the Eustachian tubes might determine the cause of dysfunction.

Magnetic resonance imaging of the eustachian tube cartilage

CONCLUSION

No useful examination was available for morphological assessment of the eustachian tube cartilage (ETC) in living subjects, but evaluation of magnetic resonance (MR) imaging enables useful assessment of the eustachian tube (ET) and ETC during preoperative examination before ET surgery.

OBJECTIVES

The objective of this study was to investigate the usefulness of MR imaging for analysis and assessment of the ETC.

SUBJECTS AND METHODS

Analysis of MR images.

RESULTS

The ETC could be demonstrated by oblique parasagittal MR imaging in most subjects, but was poorly defined in others, particularly in aged subjects. The ETC appeared as a hook-shaped structure with wide variability.

Involvement of pterygoid venous plexus in patulous eustachian tube symptoms

CONCLUSIONS

The pterygoid venous plexus (PVP) is an important factor in the mechanism of eustachian tube (ET) closure under conditions that can cause increased venous pressure in the head, such as during neck compression and postural change from the sitting/standing to the recumbent position.

OBJECTIVES

The symptoms of patulous ET are usually improved by neck compression or postural change (from sitting/standing to recumbent position). Venous congestion around the ET and/or gravitational change may be involved in the changing degree of symptoms, but its mechanism is not understood. This study investigated whether the PVP is involved.

MATERIALS AND METHODS

The dimensions of soft tissues surrounding ET were measured on magnetic resonance images before and after neck compression.

RESULTS

The lateral pterygoid muscle became enlarged after neck compression. Simultaneously, the volume of venous plexus observed between the medial pterygoid muscle and tensor veli palatini muscle was increased. Such enlargement was probably due to blood pooling in the PVP, resulting in protrusion of the ET anterior wall to the luminal side, and decreased ET patency.

Relationship between the growth pattern of nasopharyngeal cancer and the cervical lymph nodes based on MRI findings: can the cervical radiation field be reduced in patients with nasopharyngeal cancer?

To identify patients with nasopharyngeal cancer in whom the cervical radiation field can be reduced, we classified the growth patterns of nasopharyngeal cancer based on MRI findings into 4 types and performed an evaluation. Based on MRI findings, we classified the growth patterns of primary cancer in 94 patients with nasopharyngeal cancer into Type 1 (superficial type), Type 2 (lateral invasive type), Type 3 (upward invasive type), and Type 4 (anterior extension type), and further classified Type 2, based upon nasopharyngoscopic findings, into Type 2a (unilateral invasive type) and Type 2b (bilateral invasive type). The cervical lymph node metastasis areas were evaluated according to these types. Type 2 showed a significantly higher incidence of cervical lymph node metastasis only on the ipsilateral side than the other types (p = 0.0024). In particular, all patients with Type 2a had cervical lymph node metastasis only on the ipsilateral side (p = 0.0212). This study suggests that the distribution of metastasised cervical lymph nodes depends on the pattern of tumour extent of the primary site.

Sectional anatomy of auditory tube

BACKGROUND AND PURPOSE

The auditory tube connects the tympanic cavity with nasopharynx. Due to its structure and position it is difficult to demonstrate the auditory tube in its whole length, and to study its topography on anatomical specimens. The purpose of our study was to present sectional anatomy of auditory tube in order to facilitate understanding of its structure and topography.

MATERIALS AND METHODS

We utilised serial sections of cadaveric head in four planes: transverse, oblique, frontal and sagittal.

RESULTS

The osseous part of the auditory tube was demonstrated on transverse sections, and most of the cartilaginous part on oblique sections of head and neck. The tensor veli palati muscle was found to consist of bilaminar muscle sheet: the outer part originating from the skull base and the inner part originating from lateral cartilaginous lamina and membranous part of the tube. Topographic relations seen on four section planes were described in detail.

CONCLUSION

The structure, course and topography of auditory tube are well demonstrated on sectional images. Detailed knowledge of sectional anatomy of the auditory tube is important for interpretation of corresponding computerised tomographic and magnetic resonance images, and in understanding the disorders and diseases affecting middle ear and mastoid.

Unilateral palate paralysis in patients with nasopharyngeal carcinoma: imaging and clinical correlations

OBJECTIVE

Neck masses, hearing impairment, and blood-tinged nasal discharges are three major clinical manifestations of nasopharyngeal carcinoma (NPC). Because of the relationship between the anatomic structures of the fossa of Rosenmüller and the levator veli palatini muscle, NPC arising in the fossa can invade the levator muscle, limiting movement or causing paralysis of the ipsilateral soft palate. It is well known that NPC originates commonly from the fossa of Rosenmüller. We therefore hypothesize that the clinical signs of unilateral palate paralysis in patients with NPC must be far more common than usually realized. This issue is, as yet, not fully addressed in the literature.

STUDY DESIGN

A prospective study of all patients with newly diagnosed NPC.

METHODS

Two hundred sixty-four patients with newly diagnosed NPC were studied. Clinical records included the details of their clinical presentations and the results of physical and neurological examinations. The degree of elevation of the soft palate during phonation was carefully evaluated. Magnetic resonance imaging (MRI) of the head and neck region with a particular emphasis on the levator veli palatini muscles was then performed. The degree of paralysis of the palate was correlated with the degree of invasion of the levator muscles by the tumor, as seen with imaging. The incidence of paralysis of the palate in the patients with NPC was also determined.

RESULTS

At the time of diagnosis, ipsilateral paralysis of the palate was observed in 137 (52%) of the 264 patients with NPC. The results of imaging indicated that 62% (163 of 264) of the patients had radiological evidence of tumor invasion of the levator muscle. The degree of paralysis of the palate corresponded well to the extent of tumor invasion of the levator muscle. Paralysis of the palate was not evident in 26 patients with early perimuscular infiltration of the levator muscle.

CONCLUSION

This study revealed that ipsilateral invasion of the levator veli palatini muscle by NPC is common and typically presents with signs of unilateral palate paralysis. This subtle sign is relatively common in patients with NPC. Consequently, we think palate function should be routinely tested when diagnosing NPC, particularly when the patient has unilateral aural symptoms or a neck lump.

Postnatal development of eustachian tube cartilage. A study of normal and cleft palate cases

Infants with cleft palate (CP) display eustachian tube (ET) dysfunction. This study compared the postnatal development of the volume of ET cartilage in 34 normal cases and 10 CP cases using a personal computer. In cases with age under 1 month old, the total volume of ET cartilage was 61.94+/-20.89 mm(3) (mean+/-S.D.) in 16 normal control cases and 50.07+/-24.69 mm(3) in nine CP cases (t-test, not significantly different from normal). The ratio of lateral lamina (LL) to medial lamina (ML) volume (LL/ML) was reduced significantly (t-test, P<0.001) from 0.23+/-0.07 in 16 normal control cases to 0.09+/-0.05 in nine CP cases under 1 month old. In 34 normal ET cases whose ages were under 20 years, statistically significant positive correlations were found between the total volume of ET cartilage (y1) and age (x), volume of LL (y2) and age, and volume of ML (y3) and age (P<0.01, r=0.731, 0.614, 0.719). The regression lines were y1=20.37x+95.57, y2=2.02x+15.60, and y3=18. 35x+79.97. With the result obtained from this study, it is assumed that immaturity of the ET cartilage in infants, especially that of LL of the ET cartilage in CP infants, may be a significant risk factor for developing otitis media with effusion.

MR analysis of nasopharyngeal carcinoma: correlation of the pattern of tumor extent at the primary site with the distribution of metastasized cervical lymph nodes. Preliminary results

The purpose of this study was to correlate the pattern of tumor extent of nasopharyngeal carcinoma at the primary site on magnetic resonance (MR) imaging with the distribution of cervical lymph node metastasis. MR images of 32 patients with biopsy-proven nasopharyngeal carcinoma were reviewed and classified into five patterns of tumor extent in correlation with the distribution of cervical lymphadenopathy. The assessment of cervical lymph node metastasis was done on the basis of the computed tomography (CT) findings. The tumor volume was also correlated with the occurrence of contralateral lymphadenopathy. Of the 32 patients, five (16%) presented as type 1, tumor limited to the nasopharyngeal mucosa; 12 (38%) as type 2a, tumor which had invaded either lateral side but did not extend over the roof of nasopharynx; three (9%) as type 2b, tumor which had invaded bilaterally across the midline but did not extend over the roof of nasopharynx; three (9%) as type 2c, tumor which had invaded mainly the skull base but did not cross the midline; and nine (28%) as type 3, tumor which had extended anteriorly to the nasal cavity without invasion. Twenty-five patients (78%) demonstrated cervical lymphadenopathy. Patients with type 1, type 2b and type 3 spread had frequent bilateral cervical lymphadenopathy; those with type 2a had only ipsilateral lymphadenopathy. There was statistical significance (P < 0.005) regarding the existence of contralateral lymphadenopathy with midline tumors as well as the absence of contralateral cervical lymphadenopathy with non-midline tumors. This study therefore suggests that the distribution of metastasized lymph nodes depends on the pattern of tumor extent at the primary site.

Resonance imaging of the eustachian tube cartilage in microtia

OBJECTIVE

The purpose of this study was to determine whether external and internal defects in microtia are related.

METHOD

Magnetic resonance images of the eustachian tube cartilage were evaluated for 20 patients who had unilateral microtia. Nineteen patients were classified as Grade 2, and one was classified as Grade 3. The Grade 3 patient also had unilateral facial palsy.

RESULTS

On T1-, T2-, and proton-density-weighted images, the eustachian tube cartilage was clearly identified as a pair of straight lines with low signal intensity. There was no evidence of hypoplasia of the eustachian tube cartilage on the microtic side in any Grade 2 patient, but hypoplasia was evident on the microtic side of the patient classified as Grade 3.

CONCLUSION

These findings are consistent with the view that impairment of embryonic development before 6 weeks results in injury to the immature primordium and malformation of both the external and middle ear. In contrast, injuries that occur at a later fetal age (i.e., after 3 months) do not appear to cause middle ear malformations.

Serial anatomy of the auditory tube: correlation to CT and MR imaging

Serial anatomy of the auditory tube (AT), was studied in nine anatomical specimens, according to transverse, coronal and specific oblique planes and was correlated to computed tomography and magnetic resonance imaging. In order to assess the orientation of the oblique plane, parallel to the AT, 30 AT specimens were catheterized: the mean angle between the AT and the Virchow plane or the bony palate was 34 degrees. The bony portion is better explored with CT, whereas the cartilaginous portion is better studied with MR. The cartilage, posterior and medial, is closed anteriorly and inferiorly by a fibrous membrane (lamina membranacea), which is not seen on CT or MR images. The AT is closely related to the tensor veli palatini muscle (TVPM) anterolaterally, and the levator veli palatini muscle inferiorly (LVPM); both are well imaged on the oblique plane. They are bounded by fascias: the submucosal fascia (tela submucosa) is medial, the pharyngobasilar fascia runs between the TVPM and the LVPM and the auditory tube; the fascia of Weber-Liel is lateral to the TVPM. Fascias are difficult to distinguish from the surrounding fatty tissue and the adjacent muscles. The auditory tube and its muscles, forming the lateral wall of the nasopharynx, are well studied by CT and MR imaging, using the transverse or, preferably oblique plane, together with coronal plane.

Tubotympanoplasty

Prognostic value of the Eustachian tube function test remains controversial. To prevent ear drum adhesion or the recurrence of cholesteatoma it is important to select cases with severe organic obstruction of the Eustachian tube and to use surgical procedures to restore function. We summarize here the indications and the surgical procedure for organic obstruction of the Eustachian tube, especially in the region of the tympanic orifice. Adequate preoperative evaluation of Eustachian tube function and pertinent surgical procedures will pave the way for a better prognosis for patients subjected to ear surgery.

Clearance function of eustachian tube and negative middle ear pressure

Two experimental studies were performed using 18 cats in order to elucidate the mechanism of the long-lasting course of otitis media with effusion. First, the middle ear (ME) pressure was monitored for 2.5 to 7 hours after filling the whole ME space with saline. On average, -150 mm H2O of negative ME pressure was induced in 3.1 hours. Second, the residual volume of saline with antibiotics, which was put into the ME space 2 to 7 days before, was compared between the side on which tubal ventilatory function was abolished (resection of tensor veli palatini muscle and hamulus pterygoideus) and the opposite, control side. The percentage of the residual volume to the original volume put into the ME was significantly higher on the experimental side (Wilcoxon's ranking test, t = 27.0, p less than .05), and in one ear on the experimental side, the ME pressure showed-150 mm H2O just before the bulla was opened 2 to 7 days later. These results seem to indicate that tubal ciliary clearance function can induce negative ME pressure when there is fluid in the ME, and that the negative ME pressure induced by clearance of the ME fluid may disturb further clearance of the ME fluid. This condition may cause the long-lasting course of otitis media with effusion.

Histologic study of eustachian tube cartilage with and without congenital anomalies: a preliminary study

We investigated histopathologically the development of the eustachian tube (ET) cartilage at a cellular level in individuals with and without congenital anomalies. Fourteen specimens were obtained from 14 individuals ranging in age from 24 weeks' gestation to 3 years who had cleft palate or trisomy 21 (Down) syndrome; the 49 specimens in the nonanomaly (control) group were from 49 individuals ranging from 26 weeks' gestation to 85 years of age. All temporal bone specimens included the ET and its accessory structures, and all were processed and stained with hematoxylin and eosin for histologic study in a routine manner. The number of cartilage cells in the midcartilaginous portion of the ET was determined by light microscopy. In all groups, cartilage cell density of the ET decreased with increasing age. However, cell density tended to be higher at all ages for individuals with cleft palate and microtia versus controls, and tended to be lower at all ages for individuals with Down syndrome.