Schwannoma (vestibular schwannoma/acoustic neuroma) is a benign nerve sheath tumor originating from Schwann cells. Ninety percent of intracranial schwannomas arise from the vestibular nerve (CN VIII) and are located in the cerebellopontine angle (CPA). It is the most common CPA tumor (70-80%). It is usually unilateral; bilateral vestibular schwannoma is a diagnostic finding of neurofibromatosis type 2 (NF2). It typically occurs in adults aged 30-60, presenting with unilateral sensorineural hearing loss, tinnitus, and balance disturbance.
Age Range
30-70
Peak Age
50
Gender
Equal
Prevalence
Common
Schwannoma is an encapsulated benign tumor arising from Schwann cells of peripheral nerves. Vestibular schwannoma typically originates from the superior or inferior division of the vestibular nerve within the internal auditory canal (IAC) and grows medially from the IAC into the CPA — this growth pattern creates the 'ice cream cone' appearance. Histologically, it contains Antoni A (compact, fascicular) and Antoni B (loose, myxoid) areas; these two components contribute to heterogeneous signal pattern on MRI. As the tumor grows, it widens the IAC (bone remodeling), a radiological finding pathognomonic for schwannoma. Intratumoral cystic degeneration and hemorrhage may occur. The tumor displaces but does not infiltrate the nerve — it can be surgically separated from the nerve. In NF2, bilateral schwannoma results from loss of merlin (NF2 gene) tumor suppressor protein.
The spherical mass component in the CPA (ice cream scoop) together with the conical component extending into the IAC (cone) creates the 'ice cream cone' appearance. This morphological pattern is pathognomonic for vestibular schwannoma because the tumor originates from the vestibular nerve within the IAC and grows medially. Meningioma does not enter the IAC and does not show this pattern — it is the most reliable morphological criterion in differentiating extra-axial masses in the CPA. IAC widening also accompanies.
On non-contrast CT, an iso-to-mildly hypodense mass may be observed in the CPA, but small schwannomas may be missed on CT. The most valuable CT finding is IAC widening on bone window — comparison of IAC diameter with the contralateral side is critical (>2mm difference is significant). Calcification is very rare (1-2%); its presence should suggest meningioma. Bone erosion at the IAC fundus indicates the intracanalicular component of schwannoma. In large schwannomas, fourth ventricle compression and hydrocephalus may be seen. Intense enhancement is observed on contrast-enhanced CT.
Report Sentence
On bone window, right/left IAC widening is observed (diameter: _mm, contralateral: _mm), with a mass measuring approximately _x_ cm in the CPA.
On T1-weighted sequences, an iso-to-hypointense extra-axial mass relative to brain parenchyma is observed in the CPA. The mass extends into the IAC creating the 'ice cream cone' appearance — the CPA component can be imagined as the spherical ice cream scoop and the IAC component as the conical cone. This appearance is pathognomonic for schwannoma; meningioma does not enter the IAC. Intratumoral cystic areas are T1 hypointense, hemorrhagic areas are T1 hyperintense. On T1 post-contrast sequences, intense but heterogeneous enhancement is observed — Antoni A areas show intense enhancement, while Antoni B (myxoid) areas and cystic components show less enhancement.
Report Sentence
On T1-weighted sequences, an isointense extra-axial mass extending into the IAC is observed in the right/left CPA, with intense heterogeneous enhancement on post-contrast T1 sequences.
On T2-weighted sequences, schwannoma appears heterogeneously hyperintense. Antoni B (myxoid) areas are markedly hyperintense, while Antoni A (compact) areas are less hyperintense — this dual signal pattern is characteristic of schwannoma. Intratumoral cystic areas appear markedly T2 hyperintense. CSF cleft may be observed between tumor and brain parenchyma in the CPA cistern. High-resolution T2-weighted sequences (CISS/FIESTA/DRIVE) are the gold standard for evaluating the intracanalicular component — CSF-tumor contrast is excellent. Trigeminal nerve and facial nerve relationships are evaluated on these sequences.
Report Sentence
On T2-weighted sequences, heterogeneous hyperintense signal is observed in the CPA mass with cystic components and IAC extension.
Schwannomas generally show no significant diffusion restriction — ADC values are normal or elevated. This finding reflects the relatively low cellularity and loose structure of Antoni B areas. ADC is helpful in schwannoma-meningioma differentiation: meningiomas generally show lower ADC (higher cellularity). In cystic schwannomas, very high ADC values are observed in cystic components. DWI is critical in epidermoid cyst differentiation: epidermoid cyst shows markedly restricted diffusion, while the cystic component of schwannoma shows facilitated diffusion.
Report Sentence
On DWI, no significant diffusion restriction is observed in the mass, with normal/elevated ADC values — consistent with schwannoma and excluding epidermoid cyst.
On perfusion MRI, rCBV in schwannomas is generally low-to-moderate and significantly lower than meningiomas. This reflects the less vascular structure of schwannoma compared to meningioma. rCBV is useful in schwannoma-meningioma differentiation: meningiomas generally show markedly elevated rCBV (rich fibrovascular structure), while schwannomas show low-to-moderate rCBV. In cystic schwannomas, rCBV is very low in cystic components. The perfusion curve in schwannomas differs from the 'non-return' pattern of meningiomas.
Report Sentence
Perfusion MRI demonstrates low-to-moderate rCBV values in the mass, lower than expected for meningioma — consistent with schwannoma.
On MR spectroscopy, NAA is absent in schwannomas — the tumor is not of neuronal origin. Myoinositol may be elevated (Schwann cell marker). Choline is mildly elevated or at normal levels. Lipid peak may be observed in areas of cystic degeneration. Alanine peak is absent — valuable for differentiation from meningioma (alanine peak is characteristic of meningioma). MRS plays a complementary role in schwannoma vs. meningioma differentiation in CPA lesions.
Report Sentence
MR spectroscopy shows absent NAA peak, elevated myoinositol, and no alanine peak in the mass — consistent with schwannoma and against meningioma.
Criteria
Koos I: confined entirely within IAC. Koos II: extends from IAC to CPA but <2cm. Highest chance of hearing preservation surgery.
Distinct Features
Small enhancing mass within IAC on MRI. Thin-section T1 post-contrast and T2 CISS sequences are mandatory for diagnosis. No brainstem compression. Hearing may be preserved. Stereotactic radiosurgery (SRS) is an alternative treatment option.
Criteria
Koos III: tumor filling CPA but not displacing brainstem. Koos IV: tumor compressing brainstem and/or fourth ventricle (>4cm).
Distinct Features
Marked mass effect, brainstem compression, risk of obstructive hydrocephalus. Cystic degeneration and hemorrhage more common. Surgery mandatory but facial nerve preservation risk increases. Hearing loss is generally advanced.
Criteria
Schwannoma variant with prominent cystic component. Comprises 15-20% of all vestibular schwannomas. May be in the form of intratumoral cystic degeneration or peritumoral arachnoid cyst.
Distinct Features
Combination of markedly T2 hyperintense cystic component with solid enhancing component. Facilitated diffusion on DWI in cystic component (distinguishes from epidermoid cyst). Complete removal of cystic wall is important at surgery. May show rapid growth pattern.
Distinguishing Feature
Meningioma: broad-based dural attachment in CPA, dural tail, does not enter IAC, homogeneous intense enhancement, calcification possible on CT, alanine peak on MRS. Schwannoma: IAC extension (ice cream cone), IAC widening, heterogeneous enhancement, calcification rare, no alanine on MRS.
Distinguishing Feature
Epidermoid cyst: markedly restricted diffusion on DWI (bright), no enhancement, signal different from CSF on FLAIR (heterogeneity), 'cauliflower' shape. Schwannoma: no restriction on DWI, marked enhancement, IAC widening.
Distinguishing Feature
Arachnoid cyst: isointense with CSF on all sequences, no restriction on DWI, complete suppression on FLAIR, no enhancement, no IAC widening. Schwannoma: solid component present, marked enhancement, heterogeneous signal on FLAIR.
Distinguishing Feature
CPA metastasis: known malignancy history, rapid growth, no IAC widening, marked surrounding edema, may have multiple lesions. Schwannoma: slow growth, IAC widening pathognomonic, minimal edema, solitary.
Urgency
routineManagement
Tedavi seçenekleri tümör boyutu, işitme durumu ve hastanın tercihine göre belirlenir. Küçük (<1cm) asemptomatik: seri MRG ile aktif izleme. Büyüyen veya semptomatik: mikrocerrahi (retrosigmoid veya translabirintinal yaklaşım) veya stereotaktik radyocerrahi (SRS — Gamma Knife, CyberKnife). İşitme koruma cerrahisi Koos I-II'de mümkündür.Biopsy
Not NeededFollow-up
Aktif izlemede: 6 ay sonra ilk kontrol MRG, büyüme yoksa yıllık. SRS sonrası: 6 ay ve 1 yılda MRG, ardından yıllık. Cerrahi sonrası: 3 ay ve 1 yılda MRG, subtotal rezeksiyonda 6 ayda bir. NF2 hastalarında bilateral izleme ve diğer tümör taraması (meningiom, ependimom).Vestibular schwannoma is a benign tumor and many small lesions can be managed with active surveillance. Treatment decisions are determined by tumor size, growth rate, hearing status, and patient preference. SRS offers tumor control rates equivalent to surgery for <3cm tumors and is associated with lower facial nerve morbidity. Surgery is required for large tumors, but facial nerve preservation rates are inversely proportional to tumor size. Bilateral vestibular schwannoma confirms NF2 diagnosis — these patients require multidisciplinary approach, genetic counseling, and lifelong tumor surveillance.
Vestibular schwannoma is a slow-growing tumor. Small asymptomatic lesions can be monitored with serial MRI. Treatment options include microsurgical resection and stereotactic radiosurgery (Gamma Knife). Hearing loss, tinnitus, and imbalance are the most common symptoms. NF2 genetic testing should be performed when bilateral schwannomas are present.