Choroid plexus papilloma extending into the cerebellopontine angle cistern
Presentation
Two month history of generalized headache and tinnitus in the right ear.
Patient Data
Heterogenous and partially calcified lesion at the base of skull centered at the right cerebellopontine angle cistern. It appears to be contiguous with the right sigmoid sinus and right jugular foramen. Severe mass effect on the cerebellum and brainstem.
Middle ear and mastoid air cells are unremarkable. Internal acoustic canals are symmetrical in appearance.
Conclusion: Large lesion at the base of skull on the right side in the vicinity of the cerebellopontine angle cistern. Differential includes Schwannoma.
Extra-axial space occupying lesion centered at the right cerebellopontine angle cistern. It is hypointense on T1-weighted sequence and hyperintense on T2-weighted sequence relative to the brain parenchyma. There is mild restricted diffusion with homogenous contrast enhancement. No internal hemorrhagic or calcific foci.
It is causing significant mass effect on the medulla and distal pons. There is effacement of the fourth ventricle and mild obstructive hydrocephalus. At the inferior aspect it is extending through the foramen magnum with the caudal end approximately 10mm below this plane. Subtle widening of the intracranial aspect of the right jugular foramen.
Flow voids of the dural venous sinuses and major intracranial arteries maintained. Skull bones and mastoids are unremarkable. Orbital structures and paranasal sinuses are normal in appearance.
Conclusion: Large extra-axial lesion on the right side of the posterior cranial fossa centered at the cerebellopontine angle cistern with an appearance suggestive of a jugular foramen Schwannoma.
Case Discussion
The patient underwent a right-sided retrosigmoid craniotomy and resection of the lesion. Intra-operatively, this lesion at the right cerebellopontine angle cistern was found to be possibly arising from the right foramen of Luschka and the lower cranial nerves were displaced in an inferior direction due to mass effect.
Histology
Sections show fragments of a papillary tumor. The tumor forms well-formed papillae with fibrovascular cores. The cells lining the papillae are columnar or elongated, and there are areas where the cells show pseudostratification. The surface of the papillae is flat, not cobblestone in appearance. The cells have nuclei that are oval-to-bean-shaped, with relatively coarse chromatin, occasional nuclear grooves, and small nucleoli. The cells have relatively large amounts of pale eosinophilic cytoplasm. Occasional cells have clear intranuclear pseudoinclusions. The occasional mitotic figure is identified, but they are seen in numbers less than 2 per 10 high power field. There are scattered calcifications present.
- Positive
- A1/A3
- CAM5.2
- GFAP
- CK7
- Transthyretin
- Synatophysin
- Vimentin
- Negative
- CK20
- EMA
- PAX8
- SSTR2A
- PR
- Ki67 less than 5%
FINAL DIAGNOSIS: Choroid plexus papilloma (WHO grade I).
Choroid plexus papilloma is a rare intraventricular neoplasm derived from the neuro-epithelium of the choroid plexus. It may arise anywhere throughout the ventricular system but most commonly at the lateral ventricles followed by the fourth ventricle in adults 1,2,3.
Extraventricular extension of choroid plexus papilloma, such as in the cerebellopontine angle cistern, is uncommon and may be mistaken for an extra-axial lesion such as Schwannoma 4,5. This may be due to direct growth of the primary intraventricular tumor through the foramen of Luschka or from the presence of embryonic choroidal remnant projecting from the foramen of Luschka 4.
Typical findings of choroid plexus papilloma on CT include an iso- or hyperdense lobulated lesion with post-contrast enhancement. On MRI choroid plexus papilloma demonstrates an iso- or hypointense appearance on T1-weighted sequence and iso- or hyperintense appearance on T2-weighted sequence 1,2. There is moderate to strong post-contrast enhancement. Degree of heterogeneity may be influenced by the extent of intratumoral calcification, hemorrhage or necrosis 1,2,3. It is commonly associated with hydrocephalus due to a combination of increased production of CSF, reduced reabsorption by arachnoid granulation and obstruction of CSF circulation 1,2,6.
Surgical intervention is the most effective treatment of choroid plexus papilloma. Gross total resection is associated with favorable long-term survival 2,6.
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