Dr. T. Venkat Kishan Asst. Prof Department of Radiodiagnosis

Transcription

1 Dr. T. Venkat Kishan Asst. Prof Department of Radiodiagnosis

2 Schwannomas (also called neurinomas or neurilemmomas) constitute the most common primary cranial nerve tumors. They are benign slow-growing encapsulated tumors that are composed entirely of well-differentiated Schwann cells. They arise from the neural sheath, usually at the transition zone (Glial schwann cell junction)

3 Vestibular schwannoma (VS) is the preferred term for a CN VIII schwannoma. VSs are also known as acoustic schwannomas /acoustic neuromas. Focal intralabyrinthine schwannomas, also known as inner ear schwannomas, form a special subgroup of CN VIII schwannomas..

4 Adult with slowly progressive unilateral sensorineural hearing loss (SNHL) Small VSs may present initially with tinnitus. Large lesions often present with facial neuropathy

5 Peak age Adults years age Age range years Rare in children unless NF2

6 The most common tumor predisposition syndrome that causes multiple schwannomas is neurofibromatosis type 2 (NF2). The presence of bilateral vestibular schwannomas is pathognomonic of NF2. One VS and a first-degree relative with NF2 or a VS in combination with another cranial nerve schwannoma, meningioma, or glioma is also indicative of NF2.

7 VS is by far the most common intracranial schwannoma. VS is also the most common cerebellopontine cistern mass, accounting for 85-90% of lesions in this location Most common lesion in unilateral SNHL(>90%) Second most common extraxial neoplasm in adults

8 Audiometry Vestibular studies Radiological

9 CT SCAN MRI

10 Well defined enhancing mass at CPA- IAC May flare IAC when large Calcification not present (vs CP angle meningioma) Small lesions difficult to detect

11 Standard method High resolution T2 sequences (CISS or FIESTA) and Contrast enhanced sequences are routine

12 Small lesions are often completely intracanalicular. Larger lesions frequently protrude medially through the porus acusticus into the cerebellopontine angle (CPA) cistern. A schwannoma that crosses the modiolus from the cochlea into the internal auditory canal (IAC) fundus is a transmodiolar schwannoma. If a lesion crosses from the vestibule into the IAC fundus, it is termed transmacular

13

14

15

16

17

18 Virtually all VSs enhance strongly following contrast administration. A schwannoma-associated "dural tail" sign occurs but is rare compared to CPA meningiomas. Special imaging sequences may be helpful in the preoperative planning for VS surgery. MR tractography with three-dimensional tumor modeling can depict the precise location of the CNs that surround large VSs.

19 Vestibular schwannoma. A large, heterogeneously enhancing mass is seen in the right CPA. Areas of nonenhancement correspond to regions of cystic degeneration.

20 CP ANGLE SCHWANNOMA WITH ASSOCIATED ARACHNOID CYST

21

22

23

24

25 Precisely defining the size and extent of a VS is one of the most important goals of imaging.

26

27 CP Angle Meningioma Facial schwannoma Epidermoid cyst Arachnoid cyst Aneurysm Metastasis

28 The major differential diagnosis of VS is CPA meningioma. Most meningiomas "cap" the IAC and do not extend deep to the porus. Dural "tail" more common Usually more homogeneous in appearance significant heterogeneity with cystic or haemorrhagic is more typical of vestibular schwannoma than meningiomas Meningiomas tend to have a broad dural base. Calcification more common.

29 A facial nerve schwannoma confined to the IAC may be difficult to distinguish from a VS. Facial nerve schwannomas are much less common usually have a labyrinthine segment "tail.

30 Epidermoid - no enhancing component very high signal on DWI does not widen the internal auditory canal Metastasis uncommon usually does not remodel the internal auditory canal Metastases can coat the facial and vestibulocochlear nerves within the IAC. Metastases are usually bilateral with other lesions present.

31 Treatment options vary. Watchful observation of small lesions with interval follow-up imaging is common, especially in older patients. Surgical removal or stereotactic radiotherapy are other possibilities. The surgical approach of choice varies with tumor size and location, as well as whether hearing preservation is possible.

32

33 A wide variety of lesions can be encountered in the CPA. A meticulous analysis of the site of origin, shape, density, signal intensities and behaviour after contrast media injection allows a systematic approach to the preoperative diagnosis in the majority of cases

34 Acoustic Schwannomas are the most common CPA IAC mass Radiology plays a major role in the diagnosis High resolution T2 sequences (CISS or FIESTA) and Contrast enhanced sequences are routine Size and extent of the tumour is important in surgical planning

35 REFERENCES F Bonneville, Imaging of cerebellopontine angle lesion: an update. Part 1: enhancing extra-axial lesions Eur Radiol, 17 (2007), F Bonneville, Imaging of cerebellopontine angle lesion: an update. Part 2: intra-axial lesions, skull base lesions that may invade the CPA region, and non-enhancing extraaxial lesions Eur Radiol, 17 (2007), M Lakshmi, CM GlastonburyImaging of the cerebellopontine angle Neuroimaging Clin N Am, 19 (3) (2009 Aug),