choroid plexus papillomas ( cpps ) are rare benign intracranial tumors arising from the cuboidal epithelial lining of the choroid plexuses . they comprise  <  1% of all intracranial tumors and more commonly occur in childhood , although they are reported in adulthood as well.1 
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 3 cpps arise where choroid tissue is present , most commonly in the lateral ventricles in children and in the fourth ventricle in adults.4 although benign , cpps may metastasize , mandating total surgical resection if possible.5 
 6 rarely , cpps can present as cerebellopontine angle ( cpa ) tumors from direct extension of the tumor out the foramen of luschka or from seeding along cerebrospinal fluid pathways.7 
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 10 when a cpp presents as a cpa lesion , clinical diagnosis is not straightforward because symptoms from tumors in this area correlate more with which nerves and cerebral structures are involved , rather than the specific tumor type.11 radiographic appearance of this lesion can overlap with the more common cpa lesions including acoustic neuromas and meningiomas.12 
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 15 we report the case of a patient whose preoperative imaging highlighted this potential overlap . a 52-year - old woman presented to the neurosurgery clinic with a history of headaches since a ground - level fall 1  year prior . the headaches were progressively worsening and were associated with difficulty hearing and tinnitus in the right ear . the patient 's past medical history was otherwise noncontributory . on physical examination the patient was awake and alert with normal orientation and cognition . magnetic resonance imaging ( mri ) of the brain revealed a well - defined , heterogeneous 4.4    4.2    3.7 cm extra - axial cpa mass that was predominantly hypointense on t1 and hyperintense on t2 with respect to the brain parenchyma . contrast enhancement was seen extending along the posterior aspect of the internal auditory canal ( fig . 1 ) . the patient underwent a cerebral angiogram that displayed a relatively hypovascular mass in the right cpa . the right anterior inferior cerebellar artery ( aica ) was mildly displaced and was smaller in caliber as compared with the left aica . the right posterior inferior cerebellar artery ( pica ) was grossly unremarkable ( fig . ( a ) axial t2-weighted mr image displaying a well - circumscribed heterogeneous extra - axial mass centered in the right cerebellopontine angle ( cpa ) . the lesion is causing marked mass effect on the right middle cerebellar peduncle ( right brachium pontis ) and the fourth ventricle resulting in mild hydrocephalus ( not shown ) . ( b ) axial t1-weighted mr image displaying the right cpa mass to be hypointense with respect to brain parenchyma . ( c ) axial t1-weighted contrast - enhanced mr image displaying heterogeneous enhancement of the right cpa mass . in addition , there is evidence of contrast enhancement extending through the porous acusticus and along the posterior wall of the left internal auditory canal ( arrow ) . ( d ) coronal t1-weighted contrast - enhanced mr image identifying the extension of contrast into the internal auditory canal ( arrow ) . . an exaggerated transfacial view of a selective right vertebral artery injection did not show a clear area of enhancement in the right cerebellopontine angle . the caliber of the mildly displaced left anterior internal cerebellar artery ( arrow ) is smaller than the right side ( star ) . the patient was subsequently taken to the operating room and underwent a right suboccipital craniotomy via an extended retrosigmoid approach and resection of the cpa lesion ( fig . a large , soft , and vascular tumor with compression of the cerebellum medially and superiorly was resected except for a 2    2  mm piece that was left on the root entry zone of the right facial nerve . the tumor was densely adherent to the dura adjacent to the internal auditory canal ( iac ) where it had parasitized the dural blood supply . however , there was a nice arachnoidal plane between the tumor and the cranial nerve ( cn ) vii and viii complex , and the tumor was found not actually to enter into the iac . the only location that did not have a nice plane was located at the cn vii dorsal root entry zone where a 2-mm portion of tumor was coagulated but not fully resected . lower cns adherent anterior to the tumor were identified , dissected free of the mass , and preserved . following significant tumor debulking , the mass was found to be attached to choroid plexus upon its exit from the foramen of luschka . at intraoperative consultation a small biopsy of the lesion showed a cauliflower - like macroscopic appearance and yielded hypercellular diff - quik and hematoxylin and eosin ( h&e ) smears . microscopic study of the smears disclosed abundant papillary tissue fragments with bland cells arranged along vessel - centered stalks . some of the cells were surrounded by frayed cytoplasm suggesting possible neuropil elaboration , but a subsequent cryostat section disclosed that most cells possessed clearly defined cytoplasmic margins without process formation ( fig . formalin - fixed paraffin - embedded tissue sections stained with h&e disclosed a papillary neoplasm without neurophil . pseudostratified epithelial cells were seen lining the fibrovascular stalks with monotonous and eccentrically located nuclei . immunohistochemical studies for ki-67 , glial fibrillary acidic protein , and cam 5.2 were performed at our institution and showed a strong and diffuse cytoplasmic staining pattern for the latter two and a low proliferation index ( 2% qualitative estimate ) . a transthyretin ( ttr ; prealbumin ) study performed and interpreted at phenopath laboratories showed strong patchy cytoplasmic positivity . the microscopic findings and immunophenotype supported the diagnosis of a choroid plexus papilloma ( fig . one month postoperatively the patient had intact cn function with resolution of facial asymmetry and subjective improvement of hearing . ( a ) axial t1-weighted contrast - enhanced mr image displaying no residual contrast enhancement . ( b ) coronal t1-weighted contrast - enhanced mr image displaying no residual contrast enhancement . ( a ) hematoxylin and eosin ( h&e ) stain (  40 ) showing a hypercellular smear with a papillary fragment of tissue . ( b ) romanowsky stain (  200 ) showing a fibrovascular structure lined by bland , crowded , and pseudostratified epithelial cells . ( c ) h&e stain ( 400 ) showing thin cytoplasmic processes coming off bland - appearing epithelial cells . ( d ) frozen section h&e ( 400 ) showing bland epithelial cells lining a fibrovascular core with distinct cytoplasmic borders . ( a ) permanent section hematoxylin and eosin ( h&e ) (  40 ) showing fibrovascular cores lined by bland epithelial cells . ( b ) primary cpps usually develop within the ventricular system ; most tumors are located in the fourth and lateral ventricles . some of these lesions may extend from the ventricular system to extraventricular regions , but only rarely have cpps been reported to be located primarily in extraventricular regions . most primary extraventricular cpps have been reported in the cpa.16 
 17 cpps are generally solitary tumors , although multifocal presentations have been described.12 
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 19 surgical resection is the treatment of choice for cpps with radiation treatment reserved for recurrent disease.1 
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 20 because the intraoperative pathology was not consistent with a high - grade lesion , leaving a small amount of tumor adherent to the facial nerve was believed to be in the patient 's best interest keeping in mind that 5-year survival rates for cpp have been found to be 100% with gross total resection and 94% for subtotal resection , whereas a facial nerve palsy can be a significant morbidity.37 
  cpa lesions are clinically nonspecific , and the presenting symptoms are related more to the nerves or cerebral structures involved with the lesion than the nature of the lesion itself . dysfunction of hearing and facial movement , headache , dizziness , papilledema , ataxia , and hydrocephalus are common presentations of cpa cpps , although other findings have been reported including hypoglossal neuropathy and trigeminal neuralgia.7 
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 25 our patient presented with a group of nonspecific clinical signs and symptoms typical of cpa lesions that included headaches , unilateral hearing loss , tinnitus , hydrocephalus , and right facial weakness . there is no single pattern of clinical manifestations of cpa cpps such that these lesions mimic other tumors common to the cpa while others may imitate cerebellar or jugular foramen lesions . more common lesions that can present with similar clinical manifestations make up a significantly larger percentages of cpa tumors , including vestibular schwannomas ( 7080% ) , meningiomas ( 1015% ) , and epidermoid cysts ( 5%).11 the remaining cpa tumor types , including cpps , make up  <  1% each of all cpa tumors , and consequently they are challenging to diagnose . because the clinical presentations of cpa cpps are so varied , imaging studies are the primary means for preoperative diagnosis . on noncontrast head computed tomography ( ct ) , cpps are isodense to hyperdense as compared with brain parenchyma . internal calcification is present in up to 20% of cases.6 
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 22 on mri , cpps are typically isointense to hyperintense on t2 and isointense to hypointense on t1 . most cpps show robust and homogeneous enhancement on both ct and mr images.13 
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 28 in rare cases , the vascular pedicle can twist , leading to infarct of the tumor and dense calcification . heterogeneous enhancement as seen in this case is uncommon.15 
  cpps are typically quite vascular and display intense tumor blush on catheter - guided cerebral angiography.6 on cerebral angiogram , prolonged contrast enhancement , arteriovenous shunting , and enlargement of the feeding artery , aica in most cases , are typical features of cpa cpps.12 
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 30 arteriographic studies of cpp vasculature have noted consistent aica dilation with numerous and irregular feeding branches concentrated in the cpa or jugular foramen , encircling the cpps . zhang et al reviewed a series of 60 cpa tumor arteriograms that included acoustic neuromas , meningiomas , angioreticulomas , gliomas , tumors25 of the jugular foramen , chordomas of the clivus , and metastatic tumors and found that no other cpa tumor type shared the characteristic angiographic features of cpps : aica dilation with irregular dilated branches surrounding the tumor . less commonly , pica may be the primary arterial feeder of cpa cpps.6 
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 31 rarely the tumor blush is less robust and nonspecific.9 the lack of a tumor blush with a small pica as compared with the opposite side is quite uncommon for cpps . , they can have a variable appearance based on the composition of antoni type a and b cell types . these tumors are generally isointense to hypointense to the brain parenchyma on t1 and can have a heterogenous t2 signal hyperintensity . although the cystic components of the tumor tend to be t2 hyperintense , foci of microhemorrhages appear as areas of t2 signal hypointensity . after the administration of contrast , these lesions can avidly enhance . on cerebral angiogram , the imaging findings of this patient are atypical for a cpp , but they are also to some extent atypical for a schwannoma . in fig . 1 , t20weighted images appear to show the nerves of the iac with enhancement that extends into the iac exclusively along the posterior dural border , instead of circumferentially within the iac , as would be more typical of a schwannoma . the enhancement into the iac seen on brain mri in our patient is likely secondary to a reaction to the tumor involvement at the dural edge adjacent to the iac and not actually from tumor extension . a recent literature review by zimny et al suggested that although cpa meningioma , schwannoma , and cpp tumors may show a very similar appearance on conventional mr imaging , they may differ in perfusion - weighted imaging ( pwi).27 perfusion imaging can estimate the cerebral blood flow , cerebral blood volume ( cbv ) , and mean transit time of a tumor or a region of the brain . a low cbv tumor was more likely to represent a schwannoma or cpp than a meningioma . the distinction between schwannoma and cpp was less apparent based on parameters measured based on pwi . the role of mr spectroscopy ( mrs ) , which provides information about the metabolic profile of a tumor , has also been studied in distinguishing between different cpa lesions . among common cpa tumors , characteristic features include high alanine and low n - acetylaspartate ( naa ) peaks in meningiomas , high myoinositol in schwannomas , and the presence of lactate / lipid and choline peaks in metastases.11 
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 33 cpps show a characteristically high myoinositol level ( > 10 mmol / kg ) as well as a complete absence of creatine and naa.34 
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 36 thus , although mrs may help in distinguishing schwannomas from meningiomas by demonstrating a prominent myoinositol peak in schwannomas versus alanine peak in meningiomas , like relative cbv this modality can not readily differentiate cpa schwannomas from cpps , both of which demonstrate a myoinositol peak . in conclusion , we present a case of a 52-year - old woman who presented with nonspecific clinical symptoms characteristic of cpa tumors whose mri and angiographic imaging studies showed a heterogeneous enhancement and lack of a robust tumor blush . as described , these features are most consistent with a schwannoma , especially in combination with enhancement within the iac . there is considerable overlap between the perfusion and spectroscopic appearance of a schwannoma and cpp , making the impact of these modalities of questionable value . choroid plexus papilloma should be considered in the differential diagnosis of cpa masses , even in the presence of a heterogeneously enhancing hypovascular lesion .
objectives  we present the case of a choroid plexus papilloma ( cpp ) in the cerebellopontine angle ( cpa ) , describe the different appearances of cpps with a variety of imaging techniques , and discuss the differential diagnosis of cpa tumors . 
 participant and design 
 we report the case of a 52-year - old woman with headache , tinnitus , and unilateral hearing impairment whose preoperative magnetic resonance imaging revealed a heterogeneously enhancing cpa mass that extended into the internal auditory canal . 
 main outcome measures , results , and conclusion  the preoperative imaging appearance of the lesion was most consistent with that of a schwannoma . 
 postoperative histopathologic examination found the tumor to be a cpp with cuboidal epithelial cells overlying fibrovascular stroma . 
 cpps are rare benign central nervous system neoplasms arising from choroid plexus epithelium . 
 the most common site of presentation is in the fourth ventricle in adults and the lateral ventricles in children . 
 cpps rarely occur in the cpa , and when they do , clinical - radiologic diagnosis is difficult due to both the rarity of this presentation and to nonspecific radiological features .