Cerebellopontine angle (CPA) is the most common site for posterior fossa tumors, where generally 10% of all brain malignancies occur 2. The most common tumors of this region include vestibular schwannoma, which accounts for approximately 80% of the CPA tumors 2. Other common pathologies involved in this area include meningioma, epidermoid tumors, arachnoid cysts, lipoma, and metastases 11. Choroid plexus papilloma (CPP) occurs very rarely in CPA and can primarily originate from choroid plexus protruded from Foramen Luschka due to direct spread of the tumor via Foramen Luschka 18,20,35.
CPA tumors may be presented by a variety of clinical manifestations due to involvement of structures in this area, such as the effect of compression on the cerebellum and cranial nerves and branches, and the effect of compression on the brain stem (including medulla and pons).
However, given the high prevalence of schwannoma in this area, the most common manifestations are vertigo, tinnitus, and hearing loss. schwannoma is commonly associated with symptoms of tumor pressure on the surrounding structures such as unilateral hearing loss, tinnitus, and vertigo 40.
Meningioma is the second common tumor of CPA with similar clinical symptoms such as hearing loss, dizziness, tinnitus, and cerebellar symptoms, but in most cases, meningioma is detected when the tumor is enlarged and compresses nerves V and X, resulting in trigeminal neuralgia, facial numbness, facial paralysis, and swallowing impairment 11,21.
Epidermoid cysts are the third most common tumors in CPA, accounting for approximately 5% of the tumors in this area 4. Like vestibular schwannoma and meningioma, the common symptoms of these tumors are cranial nerves involvement, especially trigeminal neuralgia, hemifacial spasm, and signs of compression on the brain stem and the cerebellum 19,28.
Patients with other less common tumors, such as arachnoid cysts, have reported headache, nausea, ataxia, trigeminal neuralgia, facial numbness, hemifacial spasm, and hearing impairment 7,15.
In most cases, metastases may be confused with vestibular schwannoma; however, due to their invasive nature, the occurrence and exacerbation of symptoms of metastatic tumors in CPA are faster than other tumors 1,37.
Hydrocephalus is, by far, the most common presenting symptom for most patients with CPP 3. The mechanism of ventricular enlargement is most commonly a combination of CSF overproduction and direct obstruction of the CSF pathways by the tumor 10. The majority of patients present with insidious intracranial hypertension symptoms such as headaches, nausea, vomiting, and double or blurred vision 3.
The most common clinical symptoms of the patients pertained to symptoms of increased ICP, which was detected in 16 patients with hydrocephalus in radiological studies, although the symptoms of increased ICP were seen in 51 patients (Figure 1).
CSF overproduction is a rare condition and associated with two pathologies—choroid plexus hyperplasia (CPH; not a true tumor) and choroid plexus papilloma (CPP; typical or atypical)—both presenting in early childhood. Note that choroid plexus carcinoma (CPC) is not associated with CSF overproduction, probably because the cells lose their native ability to produce CSF. CPP may produce up to 5 liters of CSF per day often with a high protein level 6,13,30.
Hydrocephalus in patients with CPP can be attributed to different causes. However, unlike other areas such as ventricles in which overproduction of CSF is the major mechanism of hydrocephalus, hydrocephalus in patients with CPP in CPA is primarily obstructive due to the following reasons:
a) These tumors originate from choroid plexus and are active secretors of CSF; b) the tumor-induced pressure on the cerebellum and the fourth ventricle causes deformation of these structures and hence obstruct the CSF pathway; c) impairment in CSF absorption 13,30.
However, due to the limited CPA space and the effect of tumor compression in that area, obstruction, and deformation of the fourth ventricle seems to be the main mechanism of hydrocephalus in CPP in CPA.
Hydrocephaly in patients with CPP tumors in CPA is clinically important because, due to the mechanisms mentioned, even small size tumors can cause significant noncommunicating hydrocephalus that may even be one of the early symptoms of the illness. This is while hydrocephalus in other common tumors such as vestibular schwannoma and meningioma is often of the communicating type and occurs when the tumor has grown to a large extent, and the other special symptoms such as hearing impairment and other symptoms associated with tumors in this area have emerged.
Particular diagnosis of a tumor in CPA is indicated by a particular combination of symptoms and imaging findings. Vestibular schwannomas, as the most frequent CPA tumor, Symptoms are often related to cranial neuropathies. Patients are more commonly present with chronic asymmetric sensorineural hearing loss confirmed by audiometry and brainstem-evoked response audiometry (>90%) and tinnitus 9. True vertigo, unsteadiness, facial pain and numbness are unusual symptoms due to slow tumor growth 22.
As opposed to the presentation of Vestibular schwannomas, Meningiomas audiovestibular symptoms are less frequent 34. Nevertheless, Facial pain and symptoms related to cranial nerves, which are rarely seen in VS patients, are the most common presentation of cerebellopontine meningiomas 12. Cerebellar signs are frequently seen in these meningiomas compared with VSs, in which they are rare 16.
As mentioned before, the most common clinical symptoms of the patients with CPP in CPA pertained to symptoms of increased ICP. In addition, due to the origin of CPP tumors in CPA, i.e. choroid plexus and Foramen Luschka, even small tumors can be seen in these patients as involvement of nerves V, VII, VIII, and lower cranial nerves, alone or simultaneously, and the patients are manifested with symptoms such as hemifacial spasm, hemifacial numbness, hearing loss, and swallowing disorder 18,20,23,26.
These differences in symptoms combination probably could be helpful in differentiating CPA tumors.