Osseous structures in the middle ear cavity(mec): Are they too many or are they too few?

Transcription

1 Osseous structures in the middle ear cavity(mec): Are they too many or are they too few? Poster No.: C-2286 Congress: ECR 2013 Type: Educational Exhibit Authors: P. Mundada, B. S. Purohit, T. Tiong Yong; Singapore/SG Keywords: Computer Applications-3D, CT, Ear / Nose / Throat, Calcifications / Calculi, Inflammation, Infection DOI: /ecr2013/C-2286 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 30

2 Learning objectives 1. To acquaint the reader with normal anatomy and normal appearance of ossicular chain and its ligaments on CT. 2. To acquaint readers with various common and uncommon conditions which are seen as "too many" or "too few' osseus structures within MEC. Background CT is the modality of choice for temporal bone evaluation in cases of conductive hearing loss(chl) and mixed hearing loss(mhl). In these clinical scenarios, CT scan of temporal bone is performed to demonstrate integrity of ossicular chain and also to look for other causes which may present as CHL and MHL. In few instances, while evaluating the ossicular chain integrity, one or more components of ossicular chain may be found missing ("too few") or one may find extra osseous structure/s ("too many") within MEC which can cause fixation of ossicle/s. Various conditions which may present as "too few" osseous structures within MEC are: 1. Dysplasia of ossicle/s 2. Erosion of ossicle/s secondary to cholesteatoma 3. Erosion of ossicle/s secondary to infection. 4. Traumatic destruction or displacement of ossicle 5. Post-surgical. Various conditions which may present as "too many" osseous structures within MEC are: 1. Fibro-osseous tympanosclerosis 2. Congenital bony bar 3. Ossification of suspensory ligament/s 4. Ossification of stapedial tendon 5. Bone forming neoplasm in MEC Page 2 of 30

3 6. Rarely a large otosclerotic plaque may protrude in MEC. Imaging findings OR Procedure details Brief normal anatomy of ossicles, suspensory ligaemnts and tendons in MEC (1*): Anatomy of the ossicular chain is excellently demonstrated on CT. Multi planar reconstructions and 3-D images further improve delineation of smaller parts of ossicles. Use of various signs like '2 parallel lines sign' and '2 dots sign', helps in detecting subtle discontinuity of ossicluar chain. A good acquaintance with the normal appearance of various processes of ossicles and also that of ossicular joints will help in detecting presence of small erosion or ossicular dysplasia and abnormal ossification. Knowledge of the normal rate of visibility and range of variation in the appearance of the ligaments and tendons of the middle ear may be helpful in examining patients with CHL and MHL. The anterior, lateral, and superior malleal ligaments and the posterior incudal ligament are suspensory ligaments which connect the malleus and incus to the tympanic wall. The malleus and incus are connected by the incudomalleal joint, which has a capsule as well as medial and lateral incudomalleal ligaments. The incudal lenticular process and the head of the stapes are connected at the incudostapedial joint. Of these, the lateral malleal ligament is most consistently seen in its entirety. Visibility of other ligaments in entirety is variable. The stapedious tendon when seen "very well" is considered abnormal. Ligaments that are seen "too well" on high-resolution CT scans, might, in the proper clinical setting, be a sign of abnormal change. Page 3 of 30

4 Fig. 1: Icecream cone sign. Head of malleus(arrow). Body of incus(arrow head). Page 4 of 30

5 Fig. 3: 'Two parallel lines sign' (arrow). Anterior line is handle of malleus. Posterior line is long process of incus. Page 5 of 30

6 Fig. 4: 'Two dots sign'(arrow). Medial dot is head of stapes. Lateral dot is lenticular process of incus. Manubrium of malleus(arrow head)is seen anteriorly. Page 6 of 30

7 Fig. 2: Normal L-appearance of incudo-stapideal joint on coronal image. Page 7 of 30

8 Fig. 5: Superior malleal ligament (horizontal arrow). Lateral malleal ligament( vertical arrow). Tendon of tensor tympani (arrow head). References: diagnostic radiology, Changi general Hospital, singapore. - Singapore/ SG Page 8 of 30

9 Fig. 6: Anterior malleal ligament. References: diagnostic radiology, Changi general Hospital, singapore. - Singapore/ SG Page 9 of 30

10 Fig. 7: Medial posterior incudal ligament (arrow). Its lateral counterpart is almost never seen on imaging. References: diagnostic radiology, Changi general Hospital, singapore. - Singapore/ SG Page 10 of 30

11 Fig. 8: Expected location of stapedious tendon (arrow). Various conditions which may present as "too few" osseous structures within MEC are: 1. Ossicular dysplasia: Ossicular dysplasia may be associated with various syndromes st nd or may present in isolation as part of 1 and 2 branchial arch dysplasia. They are classified into four groups (2*) and the classification helps to predict the surgical outcome Class I Stapes fixation only Class II Stapes fixation with other ossicular malformation Class III ossicular malformation with mobile stapes Class IV aplasia or dysplasia of the oval or round window Page 11 of 30

12 Fig. 9: 2nd branchial arch dysplasia. Absent stapes superstructure and long process of incus. "two dots sign' and 'tow parrallel lines sign' are absent. Malleus is normal(arrow). Page 12 of 30

13 Fig. 10: Absent stapes superstructure and long process of incus(arrow). Stapes foot plate is normal (arrow head). 2. Erosion of ossicle/s secondary to cholesteatoma: Pars flaccida and pars tensa cholesteatoma are associated with retraction of tympanic membrane, chronic inflammatory soft tissue in MEC and erosions of ossicles and that of bony walls of MEC. Large erosions along the posterior wall of MEC may lead to auto mastoidectomy. Page 13 of 30

14 Fig. 11: Clinically known case of cholesteatoma. Incus is completely eroded (arrow). Absent 'ice cream cone". Malleus is intact (arrow head). Soft tissue in MEC. Temporal bone is sclerotic. Page 14 of 30

15 Fig. 12: Clinically known case of cholesteatoma. Incus and stapes super structure are completely eroded. Erosions of bony walls of MEC (arrow head). Soft tissue in MEC. Temporal bone is sclerotic. 3. Erosion of ossicle/s secondary to infection: Chronic infections of middle ear cavity are rare in adults as compared to those in children. Unsafe type of chronic suppurative otitis media (CSOM) are known be associated with erosions of bony walls of MEC and that of ossicles. Cholesteatoma may coexist with CSOM. Page 15 of 30

16 Fig. 13: CSOM in an immunocompromised young adult. Incus and stapes are destroyed. Malleus is also eroded (arrow). Tegmen tympanum is eroded (arrow head). On imaging it is indistinguishable from cholesteatoma. 4. Traumatic destruction or displacement of ossicle: Fracture of temporal bone or penetrating injury to middle ear cavity can dislodge or destroy ossicles. Page 16 of 30

17 Fig. 14: History of penetrating injury to middle ear. Absent 'two dots sign". Malleus(arrow head) and incus(arrow)are seen. Stapes is missing. References: diagnostic radiology, Changi general Hospital, singapore. - Singapore/ SG Page 17 of 30

18 Fig. 15: Stapes is displaced within the vestibule (arrow). Small speck of air is suggestive of pneumolabyrinth. 5. Post surgical: Partial or complete surgical removal of one or more ossicles and also repositioning of ossicles may be done to restore the continuity of the ossicular chain. Incus is most commonly excised or repositioned ossicle. Page 18 of 30

19 Fig. 16: Post canal wall down mastoidectomy and ossiculoplasty. 'Two parrale lines' sign is absent. Page 19 of 30

20 Fig. 17: Post canal wall down mastoidectomy and ossiculoplasty. Incus is resected and a bony bridge( arrow)is seen between the stapes head and the tympanic membrane. Various conditions which may present as "too many" osseous structures within MEC are: 1. Fibro-osseous tympanosclerosis (3*): Postinflammatory ossicular fixation shows three pathologic forms: fibrous tissue fixation (chronic adhesive otitis media), hyalinization of collagen (tympanosclerosis), and new bone formation (fibro-osseous sclerosis). Page 20 of 30

21 Tympanosclerosis appears as unifocal or multifocal punctate or weblike calcifications in the middle ear cavity or on the tympanic membrane. New bone formation (fibro-osseous sclerosis) is usually seen in the attic and is the least common manifestation. Thick bony webs or generalized bony encasement may be present at CT. Fig. 18: Background changes of chronic otitis media. New bone formation (fibroosseous fixation) is seen in the attic (arrow). Page 21 of 30

22 Fig. 19: Background changes of chronic otitis media. New bone formation (fibroosseous fixation) is seen in the attic (arrow). Head of malleus (arrow head). 2. Congenital bony bar in the MEC (4*): Congenital bony bar in the MEC is a rare condition which causes fixation of ossicle to tympanic cavity wall and results in CHL. It is differntiated from suspensory ligament ossification is on the basis of its location. Lack of background chronic otitis media differentiates it from tympanosclerosis. Page 22 of 30

23 Fig. 20: A congenital bony bar (arrow) is fixing the body of incus to the facial nerve canal. Location of bony bar excluded the possibility of ligament ossification. Lack of background chronic otitis media excludes tympanosclerosis. Page 23 of 30

24 Fig. 21: A congenital bony bar (arrow) is fixing the handle of malleus (arrow head) to the posterior wall of MEC. This condition is also known as 'Malleus bar". Its location along the expected course of chorda tympani nerve makes it indistinguishable from similar looking ossification of chorda tympani sheath, although later is an extremely uncommon condition. Location of bony bar excluded the possibility of ligament ossification. Lack of background chronic otitis media excludes tympanosclerosis. 3. Ossification / calcification of suspensory ligaments: Chronic otitis media is associated with calcification or ossification of suspensory ligaments in MEC which leads to ossicular fixation. In few circumstances exact cause of ossification of suspensory ligaments may not be known. Page 24 of 30

25 Fig. 22: Ossification of the anterior malleal ligament (arrow). A few cob-web like calcific foci (arrow head) are seen in attic, suggestive of tympanosclerosis. Page 25 of 30

26 Fig. 23: Calcification of the superior malleal ligament (arrow). Head of malleus is eroded (arrow head). Background changes of chronic otitis media are seen. 4. Congenital ossification of stapedius tendon (5*): In normal circumstances the Stapedius tendon is not seen in entirety on CT and considered abnormal whenever it is seen "too well". Congenital ossification of stapedial tendon is a rare condition which causes CHL. It is indistinguishable from a congenital bony bar in same region. Absence of background chronic otitis excluded the possibility of tympanosclerosis. Page 26 of 30

27 Fig. 24: Congenital ossification of the stapedius tendon (arrow). The stapes superstructure (arrow head) and pyramidal eminence (star) are also seen. 5. Bone forming tumor of MEC (6*): Carcinoid tumor of MEC is a rare tumor and may show calcification within. It is otherwise indistinguishable from other masses in MEC or that from chronic otitis media on the basis of imaging alone. Clinically it presents as CHL. Page 27 of 30

28 Fig. 25: Carcinoid tumor (black arrow head) with calcification (arrow) is seen in the MEC. It is indistinguishable from chronic otitis media with tympanosclerosis on imaging. Incus (white arrow head) is normal. 6. Large otosclerotic plaque projecting in the MEC: Rarely exuberant new bone formation in an otosclerotic plaque at the margin of oval window or on the footplate of stapes may appear heaped up and project in the MEC. Page 28 of 30

29 Fig. 26: Thickened footplate of stapes (arrow head). A large plaque from the posterior margin of oval window is projecting in obturator foramen of stapes (arrow). Conclusion Imaging with CT scan helps in finding cause of"too many" or "too few" osseous structures in MEC which clinically may present as CHL or MHL. References CT of the Normal Suspensory Ligaments of the Ossicles in the Middle Ear Marc M. Lemmerling,AJNR 18: , Mar /97/ ). Classification of congenital middle ear anomalies. Teunissen EB etal. Ann Otol Rhinol Laryngol.1993 Aug;102(8 Pt 1): Teunissen EB etal. Page 29 of 30

30 Postinflammatory ossicular fixation: CT analysis with surgical correlation. Swartz JD, Wolfson RJ, Marlowe FI, et al. Radiology Mar;154(3): Malleus Bar as a Rare Cause of Congenital Malleus Fixation: Yoshihisa Kurosaki, et al AJNR Am J Neuroradiol 19: , August Congenital ossification of the stapedius tendon: diagnosis with CT. Kurosaki Y et al. Radiology Jun;195(3): Carcinoid tumor of the middle ear: clinical features, recurrences, and metastases. Ramsey MJ et al. Laryngoscope 2005 Sep;115(9):1660. Personal Information Page 30 of 30