Expand The Scope of Temporal Bone Reporting: Why, What and Where to Look For.

Transcription

1 Expand The Scope of Temporal Bone Reporting: Why, What and Where to Look For. Award: Certificate of Merit Poster No.: C-1521 Congress: ECR 2014 Type: Educational Exhibit Authors: P. Mundada, B. S. Purohit, V. Thota, A. Rashad, T. Y. Tan; Singapore/SG Keywords: Trauma, Education, CT, Head and neck, Ear / Nose / Throat, Anatomy DOI: /ecr2014/C-1521 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. Page 1 of 31

2 Learning objectives The purpose of this study is to acquaint the reader with the anatomy of various clinically important intrinsic small canals and grooves of the temporal bone. After reading this exhibit, the reader will be able expand the scope of temporal bone reporting in various clinical settings like temporal bone trauma, infection, inflammation and tumours. Background High resolution computed tomography (HRCT) is the mainstay of temporal bone imaging. Since the advent of multi-detector CT (MDCT) scanners, many smaller landmarks of the temporal bone are better and more frequently visualized. Awareness of the exact anatomical location and clinical significance of these small structures is important as they may be involved in various disease processes which may affect the clinical outcome. Findings and procedure details We reviewed 50 normal CT temporal bones preformed on a 320 slice MDCT Aquilon ONE Toshiba scanner. We documented the anatomical locations of various small canals and grooves by using standard reformatted images as well as a Vitrea 3-D work station. Following small anatomical landmarks were readily seen: 1. Groove of greater superficial petrosal nerve. 2. Canal of posterior ampullary (Singular) nerve. 3. Canal of accessory posterior ampullary nerve. 4. Inferior tympanic canaliculus. 5. Canal of chorda tympani. 6. Mastoid canaliculus. Page 2 of 31

3 7. Vestibular aqueduct. 8. Cochlear aqueduct. 9. Subarcuate canaliculus. 10. Canal of cochlear nerve. 11. canal of superior vestibular nerve. 12. Canal of saccular nerve. 1. Groove for the greater superficial petrosal nerve: What and where to look for: It is a short anteromedially oriented groove seen along the anterior surface of the petrous temporal bone, extending from the geniculate fossa of the facial nerve. It is best seen on axial images. Its length is variable depending on the thickness of the bone encasing the geniculate ganglion fossa. Page 3 of 31

4 Fig. 1: Figure 1. Axial image at the level of geniculate fossa(arrow head). The groove for the greater superficial petrosal nerve (arrow)is extending antero-medially from the geniculate fossa. Why and when to look for: 1. It transmits the greater superficial petrosal nerve(gspn) and the temporal branch of the middle meningeal artery. Page 4 of 31

5 2. It is the second most common location (25%) of the facial nerve to be involved in longitudinal fracture of temporal bone. (1) 3. Fracture through the groove for GSPN may lead to impairment of ipsilateral lacrimation. (2) 4. In the setting of a middle cranial fossa mass along the anterior aspect of the petrous bone, smooth widening of the groove for GSPN indicates the diagnosis of facial nerve schwannoma. 5. In the setting of palatine cancer, posterior perineural spread causes smooth widening of groove for GSPN and suggests unresectablity. (3) 2. Canal of posterior ampullary (singular) nerve: What and where to look for: The posterior ampullary nerve (singular nerve) canal is 'J" shaped. It extends from the ampula of posterior semi-circular canal to the posterolateral wall of the internal auditory canal. It run horizontally and joins the IAC at a variable distance from the apex of IAC. It is divided in 3 segments 1. Cribriform part where it joins the ampula of the posterior semi-circular canal. 2. Intermediate part is formed by curve of the 'J'.3. Canalicular part is straight part of the 'J'. Page 5 of 31

6 Fig. 2: Figure 2. Axial image at the level of saccule. The posterior ampullary (singular ) nerve (arrow)extends from the ampulla of the posterior semicircular canal to the posterolateral wall of of the internal auditory canal. Page 6 of 31

7 Fig. 3: Figure 3. The coronal section passing through the posterior ampulla (arrow head) shows the 'J' shape of the posterior ampullary(singular) nerve (arrow). Why and when to look for: 1. In the setting of temporal bone fracture, the singular nerve canal may mimic transverse fracture. 2. A fracture through singular nerve canal may cause posterior semicircular canal dysfunction. 3. It is an important surgical land mark for retro-sigmoid acoustic neuroma surgery and trans-cochlear chochleo-vestibular nurectomy. Page 7 of 31

8 4. Singular nerve nurectomy is performed for the treatment of intractable benign paroxysmal postural vertigo. In the preoperative planning, it important to know the exact location of the intermediate part (curve of the 'J') of singular nerve in relation to the round window niche and the posterior semi-circular canal. 3. Canal of accessory posterior ampullary nerve: What and where to look for: This very thin canal is frequently seen in the otic capsule. It is best seen on axial images, near the lateral part of the IAC. Commonly, it extends from the posterior ampullary crest to the singular nerve canal (type 1). It may sometime separately open in the IAC (type 2). Rarely, it may have an independent course, parallel to the IAC, till the posterior cranial fossa (type 3). (4) Fig. 4: Figure 4: The axial image (B) shows type 2 accessory posterior ampullary nerve (arrow) which joined the posterior ampulla independent of the posterior ampullary (singular) nerve (arrow in the axial image A) Page 8 of 31

9 Fig. 5: Figure 5. The axial image shows type 3 accessory posterior ampullary nerve (arrow). It extends from the posterior ampulla (arrow head) and opens medially in the posterior cranial fossa, just posterior to the internal acoustic meatus. Why and when to look for: Page 9 of 31

10 1. It is of diagnostic importance to delineate and mention the presence of accessory posterior ampullary nerve in the clinical presentation of vestibular neuritis. Presence of dual nerve supply to the ampulla of posterior semi-circular canal may explain the preservation of the posterior semicrcular canal function in spite of loss of rest of the vestibular function. 2. In the setting of trauma, it may mimic transverse fracture of the temporal bone. 3. In the setting of post traumatic vestibular dysfunction, presence of the accessory posterior ampullary nerve may be responsible for the preservation of the posterior semicircular canal function. 4. Inferior tympanic canaliculus: What and where to look for: On axial images, the inferior tympanic canaliculus is seen arising from the lateral margin of the pars nervosa of the jugular foramen. It courses laterally along the bony ridge separating the carotid canal and the jugular foramen. It subsequently ascends and enters the middle ear cavity. Its course is better visualized on the coronal images. Page 10 of 31

11 Fig. 6: Figure 6. Axial image through the jugular foramen shows the origin of the inferior tympanic canaliculus (arrow) from the lateral margin of the par nervosa of the jugular foramen(star). It course along the bony ridge separating the internal carotid canal(bent arrow) and the pars vasculosa of the jugular foramen (white dot). Page 11 of 31

12 Fig. 7: Figure 7. Coronal image through the jugular foramen shows the origin of the inferior tympanic canaliculus ( black arrow) from the supero-lateral margin of the pars nervosa of the jugular foramen(star). It courses superolaterally and enters the middle ear cavity under the promontory (arrow).the pars vasculosa of the jugular foramen (white dot) is also seen. Why and when to look for: Page 12 of 31

13 1. It transmits Jacobson's nerve and inferior tympanic artery. 2. In the setting of trauma, the inferior tympanic canaliculus may mimic a temporal bone fracture. 3. It is one of the common locations for the occurrence of paraganglioma. 3. In the setting of mass in the middle ear cavity, its extension to inferior tympanic canaliculus should suggest paraganglioma or schwannoma of Jacobson's nerve. 4. A tubular soft tissue density structure in the middle ear cavity associated with widening of entire inferior tympanic canaliculus is diagnostic of aberrant internal carotid artery. 5. Demonstration of a normal looking inferior tympanic canaliculus confidently differentiates the lateralized internal carotid from the aberrant internal carotid artery. 5. Canal for the chorda tympani nerve: What and where to look: The canal for the chorda tympani nerve takes off from the facial nerve canal about 5 to 6 mm. It runs upward and forward and enters the tympanic cavity, through an aperture on its posterior wall, close to the medial surface of the posterior border of the tympanic membrane and on a level with the upper end of the manubrium of the malleus. It is better visualized by back and forth scrolling of the coronal images. Page 13 of 31

14 Fig. 8: Figure 8. The coronal image through the mastoid shows the origin of the chorda tympani nerve(black arrow)canal from the lateral margin of the facial nerve canal (white arrow), just above the stylomastoid foramen. Page 14 of 31

15 Fig. 9: Figure 9. Entire course of the chorda tympani nerve canal can not be seen in a axial and a coronal image. A multiplanar reconstruction image, rotated in coronal and sagittal planes, shows entire course of the chorda tympani nerve. It enters the middle ear cavity just medial to the annulus of the tympanic membrane(black arrow)canal from the lateral margin of the facial nerve canal (white arrow). Incidental inflammatory soft tissue in the middle ear cavity (star), ossicles (arrow head) and external auditory canal (white dot). Page 15 of 31

16 Why and when to look for: 1. It transmits the chorda tympanu nerve and posterior tympanic artery. 2. It may mimic a fracture in the coronal plane. 3. In the setting of trauma, fracture through the chorda tympani canal may cause loss of taste in the ipsilateral part of the tongue which often recovers spontaneously. 6. Mastoid canaliculus: What and where to look for: It is small canal courses almost horizontally from the lateral margin of the jugular foramen and joins the mastoid segment of the facial nerve canal, 5 to 6mm above the stylomastoid foramen. It is very well seen on the axial and coronal CT images. Page 16 of 31

17 Fig. 10: Figure 10. Axial image through the jugular foramen shows the origin of the mastoid canaliculus (black arrows) from the lateral margin of the pars vasculosa of the jugular foramen(star). It extends laterally to the intramastoid facial nerve canal (arrow head). Page 17 of 31

18 Fig. 11: Figure 11. Coronal image through the jugular foramen shows the origin of the mastoid canaliculus (black arrows) from the lateral margin of the pars vasculosa of the jugular foramen(star). It extends laterally to the intramastoid facial nerve canal (black arrow head). Why and when to look for: 1. It transmits the auricular branch of the glossopharyngeal nerve (Arnold's nerve). 2. In the setting of skull base fracture, the mastoid canaliculus may mimic a fracture. 3. It is one of the common location for the occurrence of paraganglioma. 7. Vestibular aqueduct: Page 18 of 31

19 What and where to look for: It is a 'J' shape canal originating from the posterior superior portion of the vestibule, near the commom crus. It courses posteriorly, inferirorly and laterally to the posterior surface of the petrous pyramid. It can be seen in segments on axial and coronal images by scrolling images. Its entire course can only be seen on sagittal oblique multiplannar reformated images. Fig. 12: Figure 12. Axial image through the basal turn of cochlea. The posterior most part of the vestibular aqueduct is seen(arrow). Page 19 of 31

20 Fig. 13: Figure 13. Coronal image through the posterior semicircular canal (black arrows). The posterior most part of the vestibular aqueduct is seen( white arrow). Page 20 of 31

21 Fig. 14: Figure 14. Multiplanar reconstructed image rotated in the coronal and sagittal plane shows the entire course of "J shaped" vestibular aqueduct(black arrows)which joins the common crus( white arrow). Why and when to look for: 1. It houses vestibular aqueduct which ends in the endolymatic sac which is seen only on MRI. Page 21 of 31

22 2. It may mimic a fracture in the setting of trauma. 3. A transverse fracture through vestibular aqueduct may cause vestibular hydrops and perilymphatic fistula which may present as fluctuating hearing loss and episodic vertigo (7) 4. Enlarged vestibular aqueduct(>1.5mm width in mid point) is associated with progressive sensorineural hearing loss. It may coexist with other congenital anomalies of inner ear. 8. Cochlear aqueduct: What and where to look for: Cochlear aqueduct is a bony canal connecting the scala tympani to subarachanoid space medially. It runs inferior and paralell to the internal auditory canal. It is bests seen by up and down scrolling of axial images, at the level of round window. Page 22 of 31

23 Fig. 15: Figure 15. Axial image caudal to the internal auditory canal. The cochlear aqueduct( black arrows)connects the subarachnoid space with the scala tympani adjacent to the round window (arrow head). Why and when to look for: 1. It houses the cochlear duct which communicated the perilymphatic space with the subarachnoid space. However, its patency and function in the normal adult ear is questionable. It also transmits the vein of cochlear aqueduct. Page 23 of 31

24 2.In pathological ears, such as those with ossicular disruption or after a type IV tympanoplasty, a patent aqueduct might affect hearing for frequencies below 150 Hz. 3. It may mimic a fracture in the setting of trauma. 4. Enlarged cochlear aqueduct is known to be associated with congenital sensorineural hearing loss. (6) 9. Subarcuate canaliculus (Petromastoid canal): What and where to look for: The subarcuate canaliculus courses between the two limbs of superior semi-circular canal. It has a characteristic anterior convexity. It is best seen on axial images. Page 24 of 31

25 Fig. 16: Figure 16. The subarcuate canaliculus (arrow) is seen between the limbs of the superior semicircular canal (arrow heads). Why and when to look for: Page 25 of 31

26 1. It transmits subarcuate artery and may have an extension of dura mater. 2. This canal can serve as a conduit for the intracranial spread of mastoid infection. 3. In the setting of trauma, it may mimic a fracture. 10. Canal of cochlear nerve: What and where to look for: It is small canal extending from the apex of the internal auditory canal to the cochlea. It is very well seen on axial and coronal images. Page 26 of 31

27 Fig. 17: Figure 17. The cochlear nerve (arrow). Why and when to look for: 1. It transmits the cochlear nerve. 2. In the setting of trauma, transverse fracture through the cochlear nerve may cause sensorineural hearing loss. 3. Cochlear nerve hypoplasia and aplasia should be excluded before cochlear implant insertion. 11. Canal for superior vestibular nerve: What and where to look for: It is a curved canal extending from the apex of internal auditory canal to superior part of the vestibule. It is very well seen in axial and coronal images. Page 27 of 31

28 Fig. 18: Figure 18. The superior vestibular nerve (arrow) and the labyrinthine segment of the facial nerve(arrow head) are seen in the same plane. Why and when to look for: 1. It transmits the superior vestibular nerve which supplies the utricle and superior and lateral semicricular canals. Page 28 of 31

29 2. A fracture through the superior vestibular nerve canal may cause dysfunction of utricle and superior and lateral semi-circular canals. 12. Canal of sacular nerve: What and where to look for: Saccular canal is short and extends from the apex of the internal auditory canal to the inferior. It is best seen on axial images. Page 29 of 31

30 Fig. 19: Figure 19. The saccular nerve (arrow) extending to the saccule. Note the posterior ampullary nerve in the same plane(arrow head). Why and when to look for: 1. It transmits saccular nerve which is one of the divisions of the inferior vestibular nerve and supplies macula of saccule. 2. Fracture through saccular nerve canal may cause post traumatic saccular dysfunction. Conclusion MDCT reformatted images and use of a 3-D work station help in better delineation of clinically important small anatomical structures of the temporal bone and thus help to expand the scope of reporting. Personal information References th 1. Peter Som, Hugh Curtin, Head and Neck Imaging, 5 edition, page 2011, Elsevier. th 2. Joel D. Swartz, Laurie A. Loevner; Imaging of the temporal bone; 4 edition. Page 451, Thieme 3. Greater Superficial Petrosal Nerve: Anatomy and MR Findings in Perineural Tumor Spread; Lawrence E. Ginsberg, Franco De Monte, and Ann Marie Gillenwater AJNR 17: , Feb Branch of the singular nerve (posterior ampullary nerve) in the otic capsule.okano Y, Sando I, Myers EN. Ann Otol Rhinol Laryngol Jan-Feb;89(1 Pt 1):13-9. Page 30 of 31

31 nd 5. Multi slice CT revised 2 edition page 80 Maximilian Reiser, M. Modic, M. Takahashi 6. Enlarged Cochlear Aqueduct; Suresh K. Mukherji, Henry C. Baggett, Jay Alley, and Vincent H. Carrasco AJNR Am J Neuroradiol 19: , February Effect of transverse temporal bone fracture on the fluid compartment of the inner ear. Rizvi SS, Gibbin KP. Ann Otol Rhinol Laryngol Nov-Dec;88(Pt 1): Page 31 of 31