Keywords
cerebellopontine angle - choroid plexus papilloma
Introduction
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]
[2]
[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]
[8]
[9]
[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]
[13]
[14]
[15] We report the case of a patient whose preoperative imaging highlighted this potential
overlap.
Case Report
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. Pupils were equal and reactive
with full visual fields. There was slight right facial weakness at the orbicularis
oris muscle. Hearing was decreased to gross testing on the right. Motor examination
was full strength throughout. Sensation was intact to light touch and pinprick.
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. This mass was compressing
the fourth ventricle and right cerebellar peduncle causing mild hydrocephalus. After
the administration of contrast, the lesion displayed moderate heterogeneous enhancement.
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. 2]). Based on the imaging appearance of this mass, it was presumed that the lesion
likely represented a schwannoma.
Fig. 1 Preoperative magnetic resonance imaging (MRI). (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).
Fig. 2 Cerebral angiogram. 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. 3]). 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.
Branches of vertebral artery, PICA, and AICA were identified and preserved. 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. 4]). 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.
There was no evidence of necrosis, neural tissue invasion, or mitosis. 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. 5]). One month postoperatively the patient had intact CN function with resolution of
facial asymmetry and subjective improvement of hearing.
Fig. 3 Postoperative magnetic resonance (MR) imaging. (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.
Fig. 4 (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. Neuropil elaboration is not identified.
Fig. 5 (A) Permanent section hematoxylin and eosin (H&E) (× 40) showing fibrovascular cores
lined by bland epithelial cells. (B) Permanent section H&E (× 100) (higher magnification
of Fig. 2A). (C) Permanent section H&E (×400) (higher magnification of Fig. 2B) showing
crowded columnar cells with a high nuclear to cytoplasmic ratio. No atypia, necrosis,
or significant mitotic activity is identified. (D) Transthyretin antibody (×200) highlighting
the epithelial cells.
Discussion
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]
[18]
[19] Surgical resection is the treatment of choice for CPPs with radiation treatment
reserved for recurrent disease.[1]
[18]
[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]
[8]
[17]
[18]
[21]
[22]
[23]
[24]
[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 (70–80%), meningiomas (10–15%), 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]
[13]
[14]
[15]
[17]
[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]
[14]
[15]
[16]
[25]
[26]
[27]
[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]
[16]
[25]
[29]
[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, tumors[25] 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]
[8]
[16]
[30]
[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.
Schwannomas are typically isodense to the brain parenchyma on noncontrast CT. Unlike
CPPs, internal calcifications are rare. On MRI, 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, schwannomas are typically hypovascular. 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]
[32]
[33] CPPs show a characteristically high myoinositol level (> 10 mmol/kg) as well as
a complete absence of creatine and NAA.[34]
[35]
[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 cannot 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.
