Anatomical variations of the human vestibular aqueduct. Part I. A radioanatomical study.

Variations in the size and shape of the human vestibular aqueduct were evaluated in 118 plastic casts of unselected specimens of human temporal bones. They were examined by conventional radiography and by high resolution CT. The degree of the mastoid and perilabyrinthine pneumatization was defined and classified into 3 types. The dimensions of the peripheral portion of the aqueduct were found to be related to the extent of the perilabyrinthine pneumatization.

Anatomical variations of the human vestibular aqueduct. Part II. A radioanatomical study.

The human vestibular aqueducts are classified into 3 types and into the types hyper-, normo- and hypoplastic. The types correspond with each other up to over 85%. For a better understanding of the radioanatomy and for the proper interpretation of radiograms, we describe the presence of a flat recess-like widening of the peripheral portion of the aqueduct, as well as other findings.

Anatomic variations of the chorda tympani canal.

The anatomic variations of the facial recess are of interest in certain otosurgical procedures. The medial border of the recess is the mastoid portion of the facial nerve canal, and the lateral border is the bony canal of the chorda tympani. These two structures were investigated in 64 polyester casts of temporal bone specimens. The point of exit of the chorda tympani canal from the facial canal was assessed together with the angle, formed between these two nerve channels. As a further way of describing the spaciousness at the facial recess, the distance between the sulcus of the stapedius muscle and the chorda tympani canal was evaluated.

The cochlea and the carotid canal.

The carotid canal conveys a large artery and lies in close topographic relationship to the basal turn of the cochlea. The bony wall between them consists in some cases only of the petrous bone of the otic capsule. It can be as thin as 0.2 mm. In other cases the distance can be more than 6 mm. A systematic assessment of the relationship between these two structures was performed on plastic casts of 173 human temporal bone specimens in order to investigate the range of normal variation. The topography in this region can be visualized by multidirectional tomography or CT.

The vestibular aqueduct in clinical radiography.

The gross morphology of the vestibular aqueduct and its clinical significance are better understood against the background of the endolymphatic duct and sac, which is still a matter of hypotheses. They are concerned with functions of the endolymphatic sac like secretion and absorption of endolymph, desintegration of cells and other debris from the inner ear and phagocytosis. The endolymphatic sac in the vestibular aqueduct is also thought to have a pressure regulation function for the labyrinth and also to deal with the metabolism of the inner ear and the desintegration of otoconia. Pathology in this area is also a matter of vital discussion. The indications for surgical intervention are consequently a matter of controversary. Radiographic research has concentrated both on the normal radioanatomy of the aqueduct and its appearances in cases of Meniere's disease and of inner ear malformations. Digression from the normal appearance can be demonstrated with multidirectional tomography and CT.

Radioanatomy of cochlear and stapedial otosclerosis.

Otospongiosis of the otic capsule is a primary focal disease, which can be reproduced by both conventional multidirectional tomography and computed tomography. The final stage of otospongiosis, otosclerosis has a complete different appearance in radiography. When the otospongiosis focus is located at the oval window a progressive conductive hearing loss will result, which in its final stage will have the character of otosclerosis with fixation of the stapes in the oval window. The radiographic diagnosis with either conventional multidirectional tomography or CT is more or less pathognomonic and will easily confirm the audiologic examinations results. The diagnosis of otospongiosis by computed tomography is advantageous to conventional tomography. With both methods high resolution technique is mandatory for safeguarding both diagnosis and evaluation of the extent of the lesion. Minor otospongiotic or otosclerotic lesions of the oval window with fixation of the footplate are still a challenge to high resolution radiographic imaging. In most cases stapedial otosclerosis is advantageously diagnosed by otoscopy and audiometry. High resolution radiographic imaging is a valuable confirmative method to corroborate clinical diagnoses and differentiating the disease from other conditions based on other morphologic lesions.

The labyrinthine portion of the facial canal. A comparative radioanatomic investigation.

The variational radiographic anatomy of the labyrinthine portion of the facial canal was investigated in 200 plastic and silicone casts of unselected temporal bone specimens by means of multidirectional and computed tomography in different projections. The labyrinthine portion of the canal varied considerably in shape and size; in some specimens the cross-section was circular, but often the canal was crumpled and flattened in its passage above the cochlea. The medial part of the labyrinthine portion was narrowest, the lowest cross-sectional area being 0.5 mm2. In spite of optimal positioning of the specimen it was not always possible to reproduce the entire labyrinthine portion of the canal completely. Most difficult to reproduce were specimens with extremely small vertical diameters and marked caudal sloping of the canal.

The labyrinthine portion of the facial canal in patients with Bell's palsy investigated by computed tomography.

The reproducibility of the labyrinthine portion of the facial canal by computed tomography was investigated in 22 patients with Bell's palsy. The CT images were compared with those obtained in 18 temporal bone specimens. Measurements of the diameters of different parts of the facial canal were made on these images and also microscopically in plastic casts of the temporal bone specimens. No marked difference was found between the dimensions of the labyrinthine portion of the facial canal of the involved and healthy temporal bone in the patient, nor did these differ from the dimensions in the specimens. CT of the slender, curved labyrinthine portion was found to be of doubtful value for metric estimation of small differences in width. The anatomic variations of the canal rendered the evaluation more difficult. CT with a slice thickness of 2 mm was of no value for assessment of this part of the canal. Measurement of the diameters of the labyrinthine portion on CT images is an inappropriate and unreliable method for clinical purposes.

From sagittal distance to area. A study of transverse, vocal tract cross-sectional area.

In speech articulation studies, data on the pharynx are scarce. Still, the pharynx is an important part of the vocal tract. The present paper reports on an attempt to use computed tomography for investigating the pharynx. Axial computed tomograms were taken at four levels in the pharynx of a male and a female subject sustaining the vowels [u:, i:, a:, oe:]. From the tomograms the lateral width and the cross-sectional area were measured and their relations to the sagittal distance from the back pharynx wall to the midline of the tongue examined and compared with previously published data. In addition, some previous results derived from plaster casts are presented showing the corresponding distance-to-area relationship in the mouth region of some male and female subjects.

The subarcuate fossa and channel. A radioanatomic investigation.

The subarcuate channel conveys the blood supply to the otic capsule of the semicircular canals, to part of the vestibule and to other neighbouring structures. It is often observed in conventional radiographs of the temporal bone and is reproduced to advantage by conventional multidirectional and computed tomography. The purpose of this report is to draw the attention of otoradiologists to this anatomic structure and to report on some results concerning the radioanatomy of the channel. Plastic casts of 100 radiographed and subsequently macerated temporal bones were evaluated. Fourteen temporal bone specimens were submitted to automatic serial cryomicrotomy. The radioanatomic variations of the channel were demonstrated. The radiographic reproducibility of the channel, length and width, were found to be dependent on the degree of perilabyrinthine and mastoid pneumatization of the temporal bone.

Effects of a high jugular fossa and jugular bulb diverticulum on the inner ear. A clinical and radiologic investigation.

From a series of patients undergoing routine radiographic examination, 112 temporal bones with a high jugular fossa were selected. Among these, 43 jugular bulb diverticula were found. The structures affected by a high fossa or diverticulum were recorded and correlated to the clinical symptoms of the patient. The vestibule was suspected to be affected in five patients. Two of these patients had tinnitus and vertigo, and three had hearing loss. In one of the latter the hearing loss was most marked in the supine position. The cochlea was close to the fossa in three patients, all of whom had tinnitus. Four patients had a defect of the posterior semicircular canal. One of them lost his hearing after a severe fit of coughing, became unsteady and showed signs of a fistula. The internal acoustic meatus and the mastoid portion of the facial canal were affected in two and four patients, respectively, who had no recorded symptoms. Twelve of 34 patients with Menière's disease and a high jugular fossa on the side of the diseased ear had a dehiscence of the vestibular aqueduct caused by the fossa or diverticulum, compared with nine of 58 patients in the unselected material. For comparison and demonstration of topographic relationships, 58 casts of unselected radiographed temporal bone specimens with high jugular fossae or diverticula were investigated. In patients with a high jugular fossa or jugular bulb diverticulum, tomographic assessment may be of value.

Investigation of temporal bone anatomy by plastic moulding and cryomicrotomy.

To increase our understanding of the complex topographic relations between temporal bone structures and to facilitate the interpretation of their radiographic images, two techniques were developed. Plastic moulding of temporal bone specimens using polyester resin and silicone rubber substances providing detailed information and a three-dimensional survey of the structures. Carefully macerated temporal bone specimens are filled with plastic material under vacuum and the bone is then dissolved. The preparations, freed from irrelevant structures and embellished, allow metric evaluation of the different structures and their topographic relations. Automatic serial cryomicrotomy of fresh, deep-frozen temporal bones, using a commercial sledge-cryomicrotome. Photography of the cut surfaces of the specimen, usually at distance of 0.25 to 0.50 mm, allows natural-colour reproduction of minute detail, e.g. the melanin cell area in the cochlea, the smallest vessels on the ossicular surfaces, and the origin of the cochlear aqueduct at the basal turn of the cochlea. By correlating the photographs with images from the corresponding tomographic planes accurate information is obtained for interpretation of the radiographic images. A combination of the two techniques facilitates a detailed study and is a valuable aid in the teaching of temporal bone anatomy.

The jugular bulb diverticulum. A radioanatomic investigation.

Two hundred and forty-five temporal bone specimens were examined radiographically. Subsequently the topographic relationship between the jugular fossa and surrounding structures was evaluated in plastic casts of the specimens. Fifty-eight casts showed a high jugular fossa and in 17 a jugular bulb diverticulum was found. A diverticulum is regarded as an anomaly of the high jugular bulb and presumably has a potential for expansion. Most frequently a diverticulum was directed medially into the space between the internal acoustic meatus, the vestibular aqueduct and the posterior cranial fossa. Seven diverticula reached the level of the internal acoustic meatus. Encroachment upon the vestibular aqueduct was seen in 4 casts and both the internal acoustic meatus and the cochlear aqueduct were very close to the diverticulum. A few diverticula were directed postero-laterally close to the facial canal and the stapedius muscle. The investigation was supplemented with a selected clinical material of radiographs of temporal bones with high fossae. The results corresponded to those of the experimental investigation. The jugular bulb diverticulum is a relatively common feature and should be regarded as an anomaly with a potential to give rise to clinical symptoms consequent to its intrusion upon surrounding structures.

The semicircular canals of the inner ear and the pneumatization of the temporal bone. A radioanatomic investigation.

In an investigation of 94 plastic casts of temporal bone specimens a wide range of variations both in the general outline of the pyramid and in the anatomy of its specific structures was found. Attempts were made to estimate the transverse and vertical dimensions of the petrous bone. Both the mastoid and the perilabyrinthine pneumatization correlated to the dimensions of some structures, but not to the size and shape of the semicircular canals.

The topographic relations of the high jugular fossa to the inner ear. A radioanatomic investigation.

The radioanatomy of high jugular fossae and their topographic relations to the inner ear structures were investigated in 245 unselected temporal bones. One hundred and fifty specimens were submitted to multidirectional and 10 to computed tomography. After careful chemical and fermentative maceration plastic casts were made, using polyester resin and silicone rubber. With the use of vacuum, even minute structures became filled with the casting material. The specimens offered a three-dimensional view of the jugular fossae and surrounding structures. Fifty-eight (24%) of the total 245 specimens had high jugular fossae at a level above the lower border of the round window. Five casts showed a dehiscence of the peripheral portion of the vestibular aqueduct caused by the high jugular fossa. In 2 casts the proximal portion of the cochlear aqueduct was affected. In some casts the posterior semicircular canal, the facial canal, the stapedial muscle and the round window lay so close to the fossa that a dehiscence could not be excluded. In a clinical material of 102 high fossae the radiographic findings were in accordance with the experimental results. High jugular fossae were predominantly found in pyramids with low-grade mastoid bone pneumatization and sparse or no perilabyrinthine air cells.

Anatomic variations of the human semicircular canals. A radioanatomic investigation.

The anatomic variations of the semicircular canals were investigated in a series of 95 plastic temporal bone preparations. The results showed a wider range of variability than has been assumed previously. An intraindividual correlation was found between the sizes of the superior and lateral semicircular canals. Observations indicate why a semicircular canal is not invariably delineated on one tomographic plane despite correct positioning for its optimum reproduction.

Anatomic variations of the human cochlear aqueduct. A radioanatomic investigation.

The cochlear aqueduct follows a course through the petrous pyramid that varies from straight and steeply vertical to a curvilinear and horizontal. Its course and length are correlated to the pneumatization of the pyramid and also to the volume of the jugular fossa. These two factors influence the radiographic reproduction of the cochlear aqueduct, especially in computed tomography in the axial transverse projection but to a far lesser degree in multidirectional tomography.

Reliability of radiographic pelvimetry. A methodological study.

The purpose of this study was to assess the reliability of radiographic pelvimetry. 48 radiologists were asked to estimate the pelvic inlet and outlet diameters from copies of 20 pelvimetry radiographs. We found that every third patient will have the sum of her pelvic outlet over- or underestimated by at least 4 mm, and 3% by more than 10 mm. The random measurement error of the sum of the pelvic outlet is about four times greater than the systematic error. The random error of the sagittal outlet diameter contributes to almost half of the total measurement error of the pelvic outlet sum. The measurement values of radiographic pelvimetry are often expressed in mm, which may give an impression of exactness that is obviously not well founded. Only in a few cases where the measurements suggest a severe feto-pelvic disproportion is it justified to do an elective cesarean section on the basis of radiographic pelvimetry only.