Mri procedure of INTERNAL ACOSTIC MEATUS

MRI Procedure of IAM

1. MRI PROCEDURE OF IAM Presenter : Sujan Karki B.Sc. MIT 3 RD Year National Academy of Medical Sciences, Bir Hospital

2. When and why MRI??? MRI is directed towards imaging of : Fluid containing spaces in temporal bones Vascular structure and their pathologies Adjacent brain parenchyma Evaluation of 7 th and 8 th cranial nerves

3. ANATOMY OF THE INNER EAR

4. Oval and round window The base of the stapes rocks in and out against the membrane in the oval window. The vibrations are transmitted from the oval window via the endolymph to the hair cells of the organ of Corti in the cochlea. The round window dissipates the pressure generated by the fluid vibrations within the cochlea and thus serves as a release valve.

5. ANATOMY OF INTERNAL ACOSTIC MEATUS

6. FACIAL NERVE

7. FACIAL NERVE

8. VESTIBULOCOCHLEAR NERVE The cochlea is positioned anteriorly to the vestibule, and the cochlear nerve occupies the anteroinferior aspect of the vestibular nerve within the  IAC. The superior and inferior vestibular nerves, as well as the cochlear nerve, join together at the opening of the  IAC , known as the porous acousticus .

9. Cerebellopontine angle meningioma in a 52-year-old woman with left sensorineural hearing loss. Axial 0.8-mm-thick SSFP MR image shows a tumor that fills the internal auditory canal (arrow) and extends into the cerebellopontine angle cistern.

10. ACOSTIC NEUROMA Tumor that develops from Schwan cells(benign) Categorized as glial cells which surrounds and supports the neurons In peripheral nervous system Schwann cell synthesize a fatty substance called myelin which acts as a insulation sheath. Vestibular schwannoma is the compression of seventh cranial nerve causing hearing loss on one side, ringing of the ear, balance problem .

11. BELL’S PALSY Weakness or paralysis of the muscles of the one side of face Cause is idiopathic(unknown) Often associated with viral and bacterial infections(  Herpes Simplex infection) A tumour compressing the facial nerve can result in facial paralysis, but more commonly the facial nerve is damaged during surgical removal of a tumour . 

12. VERTIGO Vertigo is a symptom describing the perception of space rotating on its own. Two types of vertigo Central Peripheral Central vertigo is related to brainstem and cerebellar lesions And usually accompanied by vertical movements Peripheral vertigo is related to lesions related to vestibular system and is presented with horizontal and rotational movements

13. SENSORINEURAL HEARING LOSS Caused by the lesion in the cochlea or cochlear nerve Conductive deafness is caused due to the mechanical obstruction of sound wave

14. TINNITUS Tinnitus is a sound in the head with no external source The sound may seem to come from one ear or both, from inside the head, or from a distance.  It may be constant or intermittent, steady or pulsating. One of the most common causes of tinnitus is damage to the hair cells in the cochlea

15. Meniere’s Diseases Blockage of cochlear duct Recurrent attacks of tinnitus, hearing loss and vertigo Sense of pressure in ear Distortion of sounds and sensitivity to noises Sign: ballooning of cochlear duct, utricle and saccule due to increase in endolymphatic volume.

16. MICHEL ANOMALY complete absence of  inner ear  structures

17. MICHEL ANOMALY

18. MONDINI ANOMALY

19. LABIRINTHITIS (Vestibular Neuritis) INFLAMMATION OF THE PERILYMPATHIC SPACE OF INNER EAR MAY OCCUR DUE TO INFECTIONS( VIRAL OR BACTERIAL) OR MAY BE AUTOIMMUNE. THREE STAGES ACUTE: CT appears normal ,contrast enhanced MR shows faint enhancement FIBROUS: CT appears normal , T2 weighting MR shows loss of fluid signal OSSIFICATION : inner ear structure are replaced by bones,( CT will show bone in labyrinth with loss of fluid signal on T2 weighted MR

20. Acute Stage

21. FIBEROUS STAGE

22. OSSIFICATION STAGE

23. SUPERSEMICIRCULAR CANAL DEHISCENCE SYNDROME

24. Cholesteatoma A cholesteatoma is a skin growth that occurs in an abnormal location, the middle ear behind the eardrum Cholesteatomas often take the form of a cyst or pouch that sheds layers of old skin that builds up inside the ear. usually occurs because of poor eustachian tube function as well as infection in the middle ear

25. Physics of CISS ( green sequence ) In GRE when TR <T2 relaxation time , residual transverse magnetization is left over after radiofrequency pulse. This residual transverse magnetization is not wasted but fed back in longitudinal magnetization with next RF pulse After the train of RF pulse, the repeated flipping of longitudinal magnetization into transverse magnetization and vice versa results in a non-zero steady state for both LM and TM For SSFP image formation, two types of signal are generated after each RF pulse include the free induction decay signal which has mixed T1 and T2* weighting and spin echo from prior RF pulse which has T2 weighting signal . In balanced steady state both FID and ECHO are used for image formation.

26. Continue… Gradient applied in slice selection, phase encoding and frequency encoding are balanced by gradient of opposite polarity so that there is no net dephasing of the transverse magnetization within each TR This gradient symmetry allows balanced steady state free precession to have decreased pulsation, motion and susceptibility artefact,. CISS\FIESTA-C are equivalent sequences with further modification of balanced SSFP. 2 successive 3D bSSFP sequences are acquired one with alternating flip angle (+ and -) and another with + flip angle only, which helps in the reduction of banding artefact.

27. Contrast of CISS\FIESTA-C Contrast is the ratio of T2\T1 of the tissue. Tissue with long T2 value such as water and CSF appears bright compared to sold tissue with lower T2. While fat has shorter T2 value than fluid ,its high T2\T1 ratio also results in high signal on CISS GE( GENERAL ELECTRONICS) FIESTA-C (FAST IMAGING EMPLOYING STEADY STATE ACQUISTION CYCLED PHASE) SIEMENS CISS(CONSTRUCTIVE INTERFEARENCE IN STEADY STATE) PHILIPS BALANCED FAST FIELD ECHO(B-FFE)

28. Things to do before MRI examination at waiting room …… Review the form with the patient and ask additional questions if they do have any stimulator (neuro, bone, etc.), aneurysm clips, cardiac valves, pacemakers, and any type of metallic implants such as cochlear (hearing aid) or ocular. If the patient has been or had been held a relevant job such as working in a metal factory, be extra cautious and question the patient regarding any work-related accidents. Ask patient to change clothes with MR gown and remove any metallic objects including jewelry, hair pins, watch, mobile devices, etc. Is recheck/final check necessary???Scan the patient with a metal detector one more time before taking them into the MR room What about pregnant patient???? decision makers are patients or legal guardians, but the potential advantages and risks must be explained Unconscious patient from Emergency or ICU should be screened carefully to remove metallic objects such oxygen cylinders Take the weight of the patient ????

29. PATIENT PREPARATION FOR MRI : Things to do during MRI exam at the scanner room After the screening if the patient have implants do not take him/her to scanner room until the implants MR safety is confirmed. If safe to scan then: Give and instruct the patient how to insert MR compatible spongy ear plugs to reduce the noise experienced by the patient. When you place coil, straighten the cables to avoid any loop and avoid direct contact between the cable and bare skin. Give the patient the patient alarm bell and explain them that they should press whenever they feel like they need it (burning sensation, claustrophobia, pain, nausea, etc.). To reduce the potential PNS in MRI, avoid any closed circuits or loops in patient body resulting from crossing the legs or holding hands above the head.

30. PATIENT POSITIONING

31. Localizer

32. T2 TSE AXIAL SAGITTAL: POSITION THE BLOCK PARALLEL TO GENUE AND SPLEENIUM OF CORPUS CALLOSUM. CORONAL: POSITION THE BLOCK PERPENDICULAR TO THIRD VENTRICLE AND BRAINSTEAM. AXIAL : COVER WHOLE OF BRAIN FROM VERTEX TO THE LINE OF FORAMEN MAGNUM. TR TE FA MATRIX FOV ST SG NEX 3000+ 100+ 130-150 320X320 210-230 3MM 10% 2

33. T2 TSE CORONAL AXIAL: POSITION THE BLOCK PARALLEL TO LEFT AND RIGHT IAMS. SAGITTAL: POSITION THE BLOCK PARALLEL TO THE BRAINSTEM. CORONAL :COVER THE IAMS FROM POSTERIOR BORDER OF SPHENOID SINUS TO THE LINE OF FORTH VENTRICLE TR TE FA MATRIX FOV ST SG NEX 3000-4000 110 130-140 256x256 150-180 3MM 10% 2

34. 3D CISS ( 3D SPACE OR 3D FIESTA) CORONAL: POSITION THE BLOCK PARALLEL TO LINE ALONG RIGHT AND LEFT IAMS SAGITTAL : POSITION THE BLOCK PERPENDICULAR TO BRAINSTEM. AXIAL : COVER THE IAMS FROM HIPPOCAMPUS TO THE LINE OF C1 VERTEBRAL BODY TR TE FA MATRIX FOV ST SG NEX 12-15 6-7 80 384x320 210-230 >1MM 10% 1

35. T1 TSE CORONAL AXIAL: POSITION THE BLOCK PARALLEL TO LEFT AND RIGHT IAMS. SAGITTAL: POSITION THE BLOCK PARALLEL TO THE BRAINSTEM. CORONAL: COVER THE IAMS FROM POSTERIOR BORDER OF SPHENOID SINUS TO THE LINE OF FORTH VENTRICLE TR TE FA MATRIX FOV ST SG NEX 400-600 15+ 90 320X320 210-230 3MM 10% 2

36. T1 TSE AXIAL SAGITTAL: POSITION THE BLOCK PARALLEL TO GENUE AND SPLEENIUM OF CORPUS CALLOSUM. CORONAL: POSITION THE BLOCK PERPENDICULAR TO THIRD VENTRICLE AND BRAINSTEAM. AXIAL: COVER WHOLE OF BRAIN FROM VERTEX TO THE LINE OF FORAMEN MAGNUM. TR TE FA MATRIX FOV ST SG NEX 400-600 15-25 140 256x256 170-180 3MM 10% 2

37. Ice-cream cone appearance in CT and MRI

38. Michel’s deformity Axial 3D FIESTA showing Michel's deformity on right side (red arrow) in the form of complete absence of inner ear structures.

39. Axial 3D FIESTA showing dilated endolymphatic duct on both sides

40. Cochlear ossification on both sides

41. Narrowed IAC on either side with absent B/L VCN complex

42. Vestibular Schwannoma Vestibular schwannomas represent 80-85% of the CPA tumors. Most common site of schwannoma is Scarpa's ganglion where the highest concentration of Schwann cells . The growth rate of schwannoma is variable, but usually it is slow, 1-2 mm/year. Homogenous contrast enhancement in most cases.

43. Meningioma Meningiomas are solid, well-circumscribed, and slow-growing tumors that are composed of neoplastic meningothelial cells originating from the arachnoid layer of the meninges with a broad attachment to the adjacent dura. Meningiomas are second most frequent CPA tumor H ypointense on CISS sequence obliterating the vestibulocochlear nerve Meningiomas show homogenous enhancement on postcontrast T1WI

44. Arachnoid cysts Arachnoid cysts are benign, congenital, intra arachnoidal space-occupying lesions representing 1% of all intracranial masses. They have clear CSF as its contents and do not communicate with the ventricular system.  MRI is the diagnostic technique of choice as it can demonstrate the exact location, extent, and the relationship of the arachnoid cyst to the adjacent brain or spinal cord . Determination of whether the arachnoid cyst is communicating to the CSF spaces is important in the preoperative evaluation

45. Epidermoid cysts Epidermoid cysts are congenital intradural lesions arising from the inclusion of ectodermal epithelial elements during neural tube closure. They are the third most common CPA masses after acoustic schwannomas and meningiomas.  On T1WIs, these lesions are generally slightly hyper- or iso-intense relative to the gray matter. The lesions are usually isointense relative to CSF on T2WIs, but they may be slightly hyperintense Compression of the vestibulocochlear nerve seen on CISS image Diffusion MR imaging sequence is the most important sequence in differentiating epidemoid and arachnoid cysts. Epidermoid cyst show restricted diffusion on DWI 

46. Intra-axial tumors Intra-axial tumors at CPA include medulloblastoma, ependymoma, hemangioblastoma, and metastasis. Medulloblastoma is a brain tumor of neuroepithelial origin, which represents 15-30% of a pediatric brain tumor and <1% of adult brain tumor . These are hypointense on T1WI and hyperintense on T2WI he majority of intracranial ependymomas located in the posterior fossa, which arise from the floor of the fourth ventricle.

47. References Applications of 3D CISS sequence for problem solving in neuroimaging. Divyata Hingwala ,  Somnathhatterjee ,  Chandrasekharan Kesavadas ,  Bejoy Thomas , and  Tirur Raman Kapilamoorthy . Indian J Radiol Imaging.  2011 Apr-Jun; 21(2): 90–97 Appearance of Normal Cranial Nerves on Steady-State Free Precession MR Images. Sujay Sheth ,  Barton F. Branstett , IV ,  Edward J. Escott. Jul 1 2009 High-field MRI versus high-resolution CT of temporal bone in inner ear pathologies of children with bilateral profound sensorineural hearing loss: A pictorial essay. P. Digge1 , R. K. N. Solanki2 , S. M. Paruthikunnan3 , D. S. Shah2 ; 1Manipal, Karnataka/IN, 2 Ahmedabad/IN, 3Manipal/IN. ECR 2015, Educational Exhibit Magnetic resonance imaging of cerebellopontine angle lesions. Pratiksha Yadav ,  Mansi Jantre ,   Dhaval Thakkar. : 2015 : 8 : 6: 751-759 Practical applications of CISS in MRI Imaging. Yingming Amy Chen, Daniel Chow, Jason Talbott, Christine Glastonbury, Vinil Shah. (2019) 231–242 www.kenhub.com www.medviz.com www.radiologykey.com

48. Questions Which protocol will you go for, if the patient comes for the MRI examination with the history of unilateral sensorineural hearing loss ? Explain ice-cream cone appearance in CT and MRI ? What are the common CP angle Lesions? What are the indications and contraindication of MRI IAM ? Why should we include CISS sequence in MRI of IAM?