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title: "Large IAC"
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docid: "d5405c3d-6941-4a2d-abeb-dd8ccf2b5d45"
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authors:
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- key: "eef2f839-5706-47b9-89c3-60d8315b2b3a"
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value: "Nicholas A. Koontz, MD"
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breadcrumbs:
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-
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name: "Head and Neck"
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slug: "head-and-neck"
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treeNodeId: "ed24ed8c-5d57-4629-879b-447b82d2973d"
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-
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name: "Differential Diagnosis"
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slug: "differential-diagnosis"
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treeNodeId: "40d68862-8975-4dde-ac2b-ebc43ab0fb5c"
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-
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name: "CPA-IAC and Posterior Fossa"
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slug: "cpa-iac-and-posterior-fossa"
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treeNodeId: "c590eedb-4a3b-4158-a04f-ad880564c992"
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-
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name: "Anatomically Based Differentials"
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slug: "anatomically-based-differentials"
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treeNodeId: "debfb06c-8656-4f5d-92c1-eaa468185d78"
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-
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name: "Large IAC"
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slug: "large-iac"
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treeNodeId: null
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category: "Head and Neck"
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documentVersionId: "fe254fbf-9caf-4b75-a18f-dd4c006eafc1"
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imageCount: 16
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lastUpdated: "09/04/18"
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pageDescription: "Large IAC"
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pageKeywords: "Head and Neck, Differential Diagnosis, CPA-IAC and Posterior Fossa, Anatomically Based Differentials, Large IAC"
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pageTitle: "Large IAC | STATdx"
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enhancedTitle: "Large IAC"
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type: "DDX"
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references: true
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breadcrumbs:
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- "Head and Neck"
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- "Differential Diagnosis"
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- "CPA-IAC and Posterior Fossa"
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- "Anatomically Based Differentials"
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- "Large IAC"
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---
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# ESSENTIAL INFORMATION
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- ## Key Differential Diagnosis Issues
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- Bilateral large internal auditory canal (IAC)
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- Can be normal variant if imaging otherwise normal
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- Inner ear malformation
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- Cystic cochleovestibular malformation (CCVM)
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- X-linked stapes gusher
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- Risk of CSF gusher at surgery
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- Bilateral large IAC and tumors: Consider NF2
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- Unilateral large IAC
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- Ipsilateral cerebellar hypoplasia suggests PHACES
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- Inner ear malformation, e.g., CCVM
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- Cerebellopontine angle (CPA)-IAC tumor
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- ## Helpful Clues for Common Diagnoses
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- [Vestibular Schwannoma](/document/vestibular-schwannoma/48772166-59dc-4909-bc75-538de7dd9ddf)
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- Large IAC + enhancing CPA-IAC tumor with extension along vestibular nerve(s) ± cochlear nerve
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- Variable signal on T2, depends on cellularity
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- Presence of microhemorrhages on T2* GRE or SWI may help differentiate schwannoma from meningioma in this location
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- ## Helpful Clues for Less Common Diagnoses
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- [Neurofibromatosis Type 2, CPA-IAC](/document/neurofibromatosis-type-2/cdb266b4-1e86-4dbf-a6b8-e009585e25d6)
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- Bilateral vestibular schwannomas is hallmark lesion; effectively pathognomonic
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- Bilateral vestibular > > facial or cochlear schwannomas ± schwannomas &/or meningiomas of other cranial nerves/dura
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- Unilateral or bilateral large IAC with sharply marginated tumor in CPA-IAC
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- Variable signal on T2WI, depends on cellularity
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- Intense enhancement of solid component
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- [Metastases, CPA-IAC](/document/cpa-iac-metastases/451451c8-7b49-4ce9-bf22-7c02b4652f23)
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- Uni- or bilateral large IAC due to IAC-CPA mass(es)
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- Hematogenous mets: Lytic/permeative bony destruction, hypointensity on T2WI, decreased diffusivity, and variable enhancement
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- CSF tumor dissemination of 1° intracranial tumor ± large IAC, variable MR appearance depending on tumor type
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- **PHACES Association**
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- **P**osterior fossa malformation, infantile craniofacial **h**emangioma, aortic and cerebral **a**rterial anomalies, **c**ardiac, **e**ye and **s**ternal/midline anomalies
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- Unilateral flared, large IAC
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- Ipsilateral cerebellar hypoplasia
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- ## Helpful Clues for Rare Diagnoses
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- [Schwannoma, Facial Nerve, CPA-IAC](/document/cpa-iac-facial-nerve-schwannoma/9db01630-23a4-4f42-ad83-0ec399503495)
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- Unilateral large IAC and facial nerve canal
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- **Atypical Teratoid/Rhabdoid Tumor**
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- Unilateral large IAC and IAC-CPA tumor with lytic bone destruction in infant
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- T2WI hypointensity, decreased diffusivity on DWI, and variable enhancement
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- **Cystic Cochleovestibular Malformation (IP-I)**
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- IAC most commonly enlarged; may be small or normal
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- Plump cochlea lacks internal septation/modiolus
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- Globular vestibule and lateral semicircular canal (SCC) or SCC anlage anomaly
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- [X-Linked Stapes Gusher (DFNX2)](/document/x-linked-stapes-gusher-dfnx2/498c58d9-181b-4ba7-beb8-e98cfd0bcaf6)
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- Lateral aspect IAC wide (bulbous) bilaterally
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- Corkscrew-shaped cochlea lacks normal interscalar septum and modiolus
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- **Neurofibromatosis Type 1**
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- Common disorder, wide IACs uncommon
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- Symmetric large IACs from dural ectasia **not**tumor
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## References
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# Selected References
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1. [Plotkin SR et al: Neurofibromatosis and schwannomatosis. Semin Neurol. 38(1):73-85, 2018](http://www.ncbi.nlm.nih.gov/pubmed/?term=29548054%5Bpmid%5D)
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1. [Dağkıran M et al: Radiological imaging findings of patients with congenital totally hearing loss. J Int Adv Otol. 12(1):43-8, 2016](http://www.ncbi.nlm.nih.gov/pubmed/?term=27340982%5Bpmid%5D)
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1. [Meltzer DE et al: Enlargement of the internal auditory canal and associated posterior fossa anomalies in PHACES association. AJNR Am J Neuroradiol. 36(11):2159-62, 2015](http://www.ncbi.nlm.nih.gov/pubmed/?term=26159514%5Bpmid%5D)
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1. [Wang X et al: Atypical teratoid/rhabdoid tumor (AT/RT) arising from the acoustic nerve in a young adult: a case report and a review of literature. Medicine (Baltimore). 94(4):e439, 2015](http://www.ncbi.nlm.nih.gov/pubmed/?term=25634176%5Bpmid%5D)
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1. [Saylisoy S et al: Computed tomographic findings of X-linked deafness: a spectrum from child to mother, from young to old, from boy to girl, from mixed to sudden hearing loss. J Comput Assist Tomogr. 38(1):20-4, 2014](http://www.ncbi.nlm.nih.gov/pubmed/?term=24424552%5Bpmid%5D)
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1. [Thamburaj K et al: Intratumoral microhemorrhages on T2*-weighted gradient-echo imaging helps differentiate vestibular schwannoma from meningioma. AJNR Am J Neuroradiol. 29(3):552-7, 2008](http://www.ncbi.nlm.nih.gov/pubmed/?term=18079187%5Bpmid%5D)
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1. [Kumar G et al: X-linked stapes gusher: CT findings in one patient. AJNR Am J Neuroradiol. 24(6):1130-2, 2003](http://www.ncbi.nlm.nih.gov/pubmed/?term=12812938%5Bpmid%5D)
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## Images
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### Selected Images
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**Vestibular Schwannoma**
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*Axial T1 C+ FS MR shows a large, avidly enhancing left CPA-IAC vestibular schwannoma <img src='img/arrows/WS.png'/> that markedly enlarges the IAC <img src='img/arrows/WO.png'/> as well as exerts mass effect upon the adjacent pons, brachium pontis, and cerebellum.*
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**Vestibular Schwannoma**
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*Axial T1 C+ FS MR shows a large, avidly enhancing left CPA-IAC vestibular schwannoma <img src='img/arrows/WS.png'/> that markedly enlarges the IAC <img src='img/arrows/WO.png'/> as well as exerts mass effect upon the adjacent pons, brachium pontis, and cerebellum.*
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**Neurofibromatosis Type 2, CPA-IAC**
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*Axial T1 C+ FS MR shows large CPA-IAC masses <img src='img/arrows/WS.png'/> with heterogeneous, but avid enhancement that enlarge the IACs bilaterally <img src='img/arrows/WO.png'/>. When present, the finding of bilateral vestibular schwannomas is effectively pathognomonic for the diagnosis of NF2.*
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**Metastases, CPA-IAC**
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*Axial bone NECT shows a large, destructive left petrous apex metastasis <img src='img/arrows/WS.png'/> that has eroded into and widened the left IAC <img src='img/arrows/WO.png'/>. Note the caliber of the normal right IAC <img src='img/arrows/WC.png'/> for comparison.*
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**PHACES Association**
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*Axial T2 FS MR in an infant with a facial hemangioma (not shown) demonstrates left cerebellar hypoplasia <img src='img/arrows/WS.png'/> with large retrocerebellar CSF space <img src='img/arrows/WO.png'/> and enlarged ipsilateral IAC <img src='img/arrows/WC.png'/>, a constellation of findings indicative of PHACES.*
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**Schwannoma, Facial Nerve, CPA-IAC**
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*Axial 3D T2-SPACE MR shows a CPA-IAC mass <img src='img/arrows/WS.png'/> extending along the posterior wall of the IAC to the fundus, then along the labyrinthine segment <img src='img/arrows/WO.png'/> of CNVII. Although CNVII sits anteriorly in the IAC, this schwannoma was displaced by a large cystic component <img src='img/arrows/WC.png'/> that is slightly hypointense to CSF <img src='img/arrows/BS.png'/>.*
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**Atypical Teratoid/Rhabdoid Tumor**
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*Axial bone CT in an infant with a CPA-IAC mass shows a large irregular IAC <img src='img/arrows/WS.png'/> and facial nerve canal <img src='img/arrows/WO.png'/> due to atypical teratoid/rhabdoid tumor, diagnosed following resection.*
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**Cystic Cochleovestibular Malformation (IP-I)**
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*Axial T2 MR shows a malformed, featureless vestibule and cochlea <img src='img/arrows/WS.png'/>. The wide IAC houses CNVIII <img src='img/arrows/WO.png'/> and CNVII <img src='img/arrows/WC.png'/>, which are splayed apart. Note a hypoplastic pons and a malformed cerebellum. The mastoid and middle ear fluid could be serous (common) or conceivably result from a perilymph fistula (rare).*
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**X-Linked Stapes Gusher (DFNX2)**
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*Axial bone CT in a boy with X-linked mixed hearing loss shows a wide lateral IAC <img src='img/arrows/WS.png'/>. The corkscrew-shaped cochlea <img src='img/arrows/WO.png'/> lacks internal septation or a modiolus. The wide lateral SCC is partially ossified <img src='img/arrows/WC.png'/>.*
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### Additional Images
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**Vestibular Schwannoma**
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*Axial T1 C+ MR in an ataxic teenager shows an avidly enhancing mass widening the CPA cistern <img src='img/arrows/WS.png'/>, distorting the pons, and expanding the IAC <img src='img/arrows/WO.png'/>, consistent with schwannoma, which was confirmed after resection.*
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**Neurofibromatosis Type 2, CPA-IAC**
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*Axial T1 C+ FS MR in a patient with NF2 shows bilateral, avidly enhancing IAC tumors extending into the left cochlear canal <img src='img/arrows/WS.png'/> and along the vestibular nerves <img src='img/arrows/WO.png'/>. A V3 schwannoma is also seen <img src='img/arrows/WC.png'/>.*
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**Neurofibromatosis Type 2, CPA-IAC**
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*Axial 3D T2 SPACE MR in a teenager with NF2 shows bilateral IAC-CPA schwannomas in widened IACs <img src='img/arrows/WS.png'/>. There is also a V3 schwannoma in the foramen ovale <img src='img/arrows/WO.png'/>.*
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**Metastases, CPA-IAC**
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*Axial T1WI C+ FS MR in an infant with otalgia and CNVII palsy shows an enhancing tumor expanding the IAC <img src='img/arrows/WS.png'/> and CPA cistern, invading the petrous apex <img src='img/arrows/WO.png'/>, CNVII <img src='img/arrows/WC.png'/>, and the middle ear space. Bony destruction was seen on CT. The differential diagnosis included rhabdomyosarcoma, ATRT, or metastases. A final diagnosis of metastatic neuroblastoma was made after middle ear biopsy.*
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**Metastases, CPA-IAC**
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*Coronal T2 FSE MR shows a patient with CSF dissemination of glioneuronal neoplasm. The hyperintense tumor filling the widened IACs <img src='img/arrows/WS.png'/> is hard to distinguish from CSF on this image but was more evident on FLAIR images. The patient had large IACs at the time of presentation. As CSF tumor dissemination/metastatic disease occurred, the IACs showed progressive massive enlargement over time on successive MR studies.*
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**PHACES Association**
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*Axial T2 MR in an infant with a facial hemangioma <img src='img/arrows/WS.png'/> shows left cerebellar hypoplasia <img src='img/arrows/WO.png'/> with a prominent adjacent CSF space, large flared left IAC <img src='img/arrows/WC.png'/>, and enlarged Meckel cave <img src='img/arrows/BS.png'/>.*
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**Cystic Cochleovestibular Malformation (IP-I)**
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*Axial bone CT in a patient with profound SNHL shows an enlarged vestibule <img src='img/arrows/WS.png'/> and lateral SCC <img src='img/arrows/WO.png'/> with an enlarged IAC <img src='img/arrows/WC.png'/>. Extensive opacification of the mastoid air cells and middle ear space is also seen.*
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**Neurofibromatosis Type 1**
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*Axial T2 MR in a teenager with NF1 shows large IACs bilaterally with no evidence of inner ear anomaly or IAC mass lesion. This is a feature of mild dural ectasia in NF1.*
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