Acoustic schwannoma (Dr. Mahesh)
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1. Acoustic neuromas, also known as vestibular schwannomas, are benign tumors that originate from the Schwann cells of the eighth cranial nerve. 2. They typically present with symptoms of unilateral hearing loss, tinnitus, imbalance, and fullness in the ear. Larger tumors can cause additional symptoms by compressing nearby cranial nerves and brain structures. 3. Diagnostic imaging includes CT, MRI, and audiological tests. MRI is the preferred imaging method as it can clearly depict the size, location, and extent of the tumor. Surgical resection is the primary treatment, while stereotactic radiosurgery techniques like gamma knife are alternatives for patients who cannot undergo
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Acoustic schwannoma (Dr. Mahesh)
- 1. Dr. Mahesh Chaudhary Resident, Phase-B
- 2. Acoustic Neuroma • Definition: Tumour of eighth cranial Nerve Originate from Schwann cell • Eponyms: Vestibular Schwannoma Neurilemmoma
- 3. Pathology • Gross: Benign, Encapsulated, Slow-growing Cystic/Fatty degeneration Haemorrhagic necrosis • Microscopy: Elongated spindle cells Rod-shaped nuclei in rows or palisades. Antoni type A & B
- 4. Classification Acoustic Neuroma Intracellular Small Size <1.5cm Medium size 1.5-4cm Large Size > 4cm
- 5. Incidence • 75-80% of Cerebellopontine angle tumors • 6-8% of all brain tumors • Multiple schwannomas (5%) & characteristic of NF-2 • Prevalent in older age (5th to 6th decades) • With NF-2, it appears earlier, 3rd decade • Slight female predominance(1.5-2:1)
- 6. Location • All cranial nerves except the 1st and 2nd CN • Arise eccentrically from the outer nerve sheath layer • Have a distinct propensity to affect sensory nerves more than pure motor nerves. • CN VIII is the most commonly affected, followed by trigeminal nerve root or ganglion
- 7. CN involvement Vestibulocochlear nerve: 90-95% schwannomas • Originate in inferior or superior vestibular division • Cochlear schwannomas are rare Trigeminal nerve : 5-6% schwannomas • Most common location is the middle cranial fossa • Dumbbell"- shaped or "hourglass" tumors
- 8. CN….. • Facial nerve: 3rd most common site • Most facial schwannomas are intratemporal • All segments of intrapetrous facial nerve can be affected, although the geniculate ganglion is the most frequent site.
- 9. Natural history • Schwannomas are slow growing benign neoplasms. • Potential for regrowth after incomplete excision • Rarely undergo malignant degeneration
- 10. Clinical Features • Age : 50-60 years • Sex: F>M. ?M=F • Symptoms: 1. Progressive unilateral SNHL 2. Tinnitus 3. Marked difficulty in understanding speech 4. Imbalance/ Unsteadiness 5. Vertigo 6. Sudden Hearing loss 7. Fullness in the ear
- 11. Cranial Nerve Involvement 1. 5th nerve: Reduced cornea sensitivity, paraesthesia of face Involvement indicates : tumour size = 2.5cm & occupies CP angle 2. 9th & 10th : dysphagia & hoarseness due to palatal, pharyngeal, laryngeal paralysis 3. Other cranial nerves: affected only when tumour size is very large
- 12. Cranial Nerve Involvement Facial nerve: • Sensory fibres are affected early. • Hitzelberger’s sign : Hypoaesthesia of posterior meatal wall • Loss of taste ( Electrogustometry) • Schirmer test : Reduced lacrimation • Motor fibres: Affected late • Delayed blink reflex
- 13. Brainstem Involvement • Ataxia • Weakness & Numbness of arms and legs • Exaggerated tendon reflexes Raised Intra-cranial tension Headache, nausea, vomiting, diplopia(6th) & papillo-edema with blurring of vision.
- 14. Cerebellar involvement • Pressure symptoms on cerebellum are seen in large tumors • Revealed by Finger-nose test Knee-heel test Dysdiadochokinesia Ataxic gait Inability to walk along a straight line (tendency to fall on the affected side)
- 15. Investigations • Audiological tests: 1. PTA 2. Speech Audiometry 3. Recruitment phenomena: Absent 4. Short Increment Sensitivity Index: 0-20% 5. Threshold tone decay test : Retrocochlear type of lesion
- 16. Vestibular Tests • Caloric test: Diminished or absent response in 96% of patients May be normal when tumour is small
- 17. Plain X-ray • Bone changes are late manifestations • Widening of the internal auditory canal can be seen with moderate-sized acoustic schwannomas • Smooth, sharply marginated, anteromedial petrous apex erosion is the most common in trigeminal schwannoma • Enlarged foramen ovale, foramen rotundum, or superior orbital fissure. • Hyperostosis and bone sclerosis are rare.
- 18. CT scan • Iso- or slightly hypodense on NECT scans • Enhance strongly after contrast administration • Calcification and haemorrhage: uncommon. • Trigeminal schwannomas with longstanding denervation cause atrophy and fatty degeneration of the masticatory muscles
- 19. CECT: NF-2
- 21. MRI • Demonstrate an extra-axial mass • Have distinct CSF/vascular "cleft" between tumor and brain • Cortico-medullary junction of the cerebellum is displaced, and the brainstem appears rotated • Form an acute angle with the petrous temporal bone. • The cisternal portion is typically larger than the intracanalicular segment: “ice cream on a cone”
- 22. • T1WI :2/3rd hypointense, 1/3rd are isointense. • T2WI & FLAIR: mild to markedly increased signal intensity • After contrast: -intense enhancement (67%) -mildly inhomogeneous in (10%) -heterogeneous with areas of intratumoral cystic degeneration (22%) • Cystic degeneration are common in larger lesions but frank hemorrhage is rare (5%) • Peritumoral edema is seen in 37% • Associated with arachnoid cysts in 7% of cases
- 25. Differential Diagnosis • Meniere’s Disease • Tumours of CP angle: 1. Meningioma 2. Epidermoid 3. Arachnoid Cyst 4. Schwannoma of other cranial nerves 5. Vascular (Aneurysm) 6. Metastasis
- 28. Surgical • Treatment of Choice Approaches Middle Cranial Fossa Translabyrinthine Suboccipital Combined translabyrinthine- suboccipital
- 29. Radiotherapy 1. Conventional Radiotherapy 2. ɣ-knife surgery 3. Cyber knife
- 30. ɣ-knife surgery • Stereotactic radiotherapy • Advantages: 1. Minimal radiological effect 2. Causes reduction in tumour size & growth. 3. Can be used in patients where surgery is not feasible. • Procedure : linear accelerator ɣ-knife through cobalt-60
- 31. Radiotherapy Conventional: • Not preferred now due to low tolerance of CNS to radiation Cyber knife: • Modified X-knife • More accurate & frameless • Method: real-time image guidance technology through computer controlled robotics.
Editor's Notes
- Antoni type A has compact interlacing bundles of fusiform neoplastic Schwann cells, reticulin, and collagen. When well-developed - "Verocay bodies,“ Antoni type B consists of a loosely textured stroma with widely separated stellate cells and no distinctive pattern are prone to cystic degeneration.
- all cranial nerves 3-12 have sheaths that are partially composed of Schwann cells and are therefore potential sites for intracranial schwannomas. Arise eccentrically from the outer nerve sheath layer and enlarge away from it, compressing rather than invading the nerve
- Recruitment causes your perception of sound to be exaggerated. Even though there is only a small increase in the noise levels, sound may seem much louder and it can distort and cause discomfort. the sounding of a continuous tone at threshold for 1 min; if the intensity must be increased by more than 5 dB for continued perception, it is indicative of a neural hearing loss.
- Normal body 37 Cold -7 = 30, Hot +7 = 44 Normal person produces nystagmus
- Small tumors usually show uniform enhancement, whereas larger lesions may have a heterogeneous pattern. This is due to cystic degeneration, xanthomatous change, or areas of relative hypo cellularity adjacent to densely cellular or collagenous regions (Antoni type B)
- A patient with NF-2, having bilateral schwannomas, right one having intra cannilicular extension
- Facial schwannoma in a woman with a history of slowly progressive left facial paralysis. A, Highresolution axial CT scan of the skull base through internal auditory canals. In left, geniculate ganglion and the horizontal facial nerve canals are enlarged (black arrowheads). There is opacification of the middle ear and mastoid. B, Axial section at the level of the external auditory canal. The left descending facial nerve canal (black arrow) is much larger than the right (black arrowhead)
- Fascicular sign is a finding on T2-weighted MRI images that suggests a lesion of neurogenic origin. It is characterised by multiple small ring-like structures with peripheral hyperintensity representing the fascicular bundles within the nerves. It is found in various neurogenic tumours, including: neurofibroma schwannoma / neurilemoma malignant peripheral nerve sheath tumour (PNST): a spindle cell carcinoma arising from a nerve or a neurofibroma
- split-fat sign: thin peripheral rim of fat best seen on planes along long axis of the lesion in non-fat-suppressed sequences target sign peripheral high T2 signal central low signal rarely seen intracranially fascicular sign: multiple small ring-like structures
- Image B: Axial C++ T1WI…… The tumour enhances strongly but heterogeneously Intracanalicular part of the tumour (curved arrow). Also note the compressed fourth ventricle (anowhead) and rotated brainstem. Image C: Axial T2WI…. large acoustic schwannoma.. It is slightly hyper intense to brain inT2WI and-has numerous inhatumoral cysts (open arrows).
- A, Axial T1-weighted MR image acquired after contrast through the IACs. Both tumors of CP angles are enhancing, right shows greater enhancement. B: Axial T2-weighted MR image acquired through the internal auditory canals (IACs). Filling defects are seen in both IACs. The mass on the right is larger and extends out into the cerebellopontine angle. Bilateral acoustic tumors suggest neurofi bromatosis type 2
- meningioma usually more homogeneous in appearance: significant signal heterogeneity with cystic or haemorrhagic areas is more typical of vestibular schwannoma than meningiomas (although cystic meningiomas do occur) meningiomas tend to have a broad dural base usually lack the trumpeted internal acoustic meatus sign calcification more common 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, as metastases are usually present for only a short time ependymoma centred on the fourth ventricle does not extend into the internal auditory canal usually younger patients
- meningioma usually more homogeneous in appearance: significant signal heterogeneity with cystic or haemorrhagic areas is more typical of vestibular schwannoma than meningiomas (although cystic meningiomas do occur) meningiomas tend to have a broad dural base usually lack the trumpeted internal acoustic meatus sign calcification more common 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, as metastases are usually present for only a short time ependymoma centred on the fourth ventricle does not extend into the internal auditory canal usually younger patients