(Figs. 7 and 8)
Acoustic schwannoma Most common mass, up to 75% of cases Meningioma Second most common lesion, up to 10% of cases Ectodermal inclusion
tu-mors
– Epidermoid Also known as “congenital cholesteatoma” or “pearly tumor”; 5 – 7%
– Dermoid Metastases
Paraganglioma Also known as “glomus jugulare tumor”; a chemodec-toma arising from the jugular foramen and extending into the CPA; 2 – 10%
Other schwannomas 2 – 5%. The trigeminal and facial nerves are probably the most common sites of nonacoustic schwannomas.
Other cranial nerves involved are: VI, IX, X, XI, and rarely XII
Vascular 2 – 5%
– Dolichobasilar
ec-tasia 3 – 5%
– Aneurysm 1 – 2%
– Vascular
malforma-tion 1%
Choroid plexus
papil-loma 1%; primary in the CPA or extension via the lateral foramina of Luschka
Ependymoma 1%; extension from the fourth ventricle Rare lesions Incidence ! 1%
– Arachnoid cyst – Lipoma
– Exophytic brain stem or cerebellar astrocytoma – Chordoma
– Osteocartilaginous tu-mors
– Cysticercosis CPA: cerebellopontine angle.
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CPA cistern
AICA
Pons CN VII CN VIII
4th ventricle temporal lobe
temporal bone
cochlea
vestibule (semicircular canal)
jugular foramen cerebellum
Fig. 7 Cerebellopontine angle. Diagram of the cerebellopontine angle anat-omy
Fig. 8 Cerebellopontine angle lesions
1. Acoustic neurinoma. Axial CT with right acoustic neurinoma and erosion of the internal auditory meatus with a small protrusion of the tumor in the cerebellopontine angle.
2. Erosion of the auditory meatus. Bone windows of an axial CT of the same patient with an abnormal erosion of the right internal auditory meatus.
3. Acoustic neurinoma. A solid space-occupying mass with mild postcontrast enhancement producing erosion of the right acoustic meatus, protrusion into the right CP angle, and compression of the pons and cerebellar peduncles.
4. Chordoma. Axial T1 WI shows a solid, space-occupying lesion with postcon-trast enhancement occupying the left middle temporal fossa and ipsilateral
Cerebellopontine Angle
5, 6. Meningioma. Axial and coronal T1 WI with a postcontrast enhancing meningioma of the right CP angle that extends into the right jugular fora-men causing compression of the medulla oblongata and the right cerebellar hemisphere.
7. Epidermoid tumor. Coronal T1 WI with a cystic space-occupying, nonen-hancing lesion in the right CP angle with compression signs of the pons.
8. Epidermoid tumor. A solid and heterogeneous mass with smooth margins eroding the left occipital bone and compressing the left cerebellar hemi-sphere is seen on axial T1 WI.
Fig. 8
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Internal Auditory Meatus
Neoplastic masses – Intracanalicular
acous-tic Schwannoma – Facial schwannoma – Lipoma
– Meningioma – Hemangioma – Lymphoma Nonneoplastic masses – Postoperative
reac-tive dural fibrosis The second most common cause of enlargement of the internal auditory meatus
– Neuritis Bell’s palsy, Ramsay Hunt syndrome or herpes zoster otitis, and viral infections are benign conditions that can cause cranial nerve enlargement
– Meningitis – Sarcoidosis
– Vascular Hemorrhage, vascular loop of AICA, AVM or aneurysm AICA: anterior inferior cerebellar artery; AVM: arteriovenous malformation.
Foramen Magnum
(Figs. 9 and 10)
Intra-axial cervicomedullary masses Nonneoplastic
– Syringomyelia In 25% of Chiari I patients; secondary syrinxes due to trauma can be seen
– Demyelinating
dis-eases ! Multiple sclerosis
! Acute transverse myelopathy
! Miscellaneous (e.g., radiation, AIDS, vascular AVM) Neoplastic
– Gliomas,
astrocy-tomas Commonly of low grade, 50% occurring in the cervi-comedullary junction. Extension of spinal cord gliomas into this area is also common. Other types of gliomas, however, such as anaplastic astrocytoma, gangliogan-glioma, ependymoma are also found here
– Nonglial neoplasms Inferior extensions of medulloblastomas in children and hemangioblastomas in adults are common in this area
– Metastases Rare
Foramen Magnum
optic
recess infundibular recess optic
chiasm
superior & inferior colliculi Great cerebral vein of Galen straight sinus
Transverse sinus (sectioned) occipital bone 4th ventricle
cisterna magna C1 (posterior arch) C2 anterior
commissure posterior commissure
pineal gland splenium of corpus callosum
tentorium cerebelli
PICA (posterior inf.
cerebellar artery) C1 (anteriorarch)
Fig. 9 Intracranial tumors. Midsaggital anatomic diagram of the pineal and foramen magnum regions
Fig. 10 Foramen magnum "
1. Glioma of the high cervical spinal cord (C2), producing a focal expansion of the spinal cord, is seen on this midsagittal T1 WI.
2. Meningioma. Axial CT demonstrates a calcified meningioma of the posterior part of the foramen magnum compressing the medulla oblongata.
3. Epidermoid cyst. Axial CT with a cystic lesion of the foramen magnum causing compression of the medulla oblongata.
4. Chiari II malformation. Sagittal T1 WI shows a descent of the cerebellar tonsils and compression of the medulla oblongata and associated syringomyelia.
5. Osteolysis of C2 and a mass of soft tissues producing compression and dis-placement of the spinal cord is seen on coronal T1 WI.
6. Atlantoaxial subluxation. Sagittal T2 WI shows atlantoaxial subluxation with the development of inflammatory tissue around the dens of C2. This pathology causes stenosis of the foramen magnum and compression of the spinal cord and lower medulla. Focal myelinolysis is indicated by a high inten-sity signal.
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121 Internal Auditory Meatus
Anterior extramedul-lary intradural masses Ectatic vessel, aneurysm
The most common mass anterior to the medulla is a tortuous, ectatic vertebral artery. Occasionally, aneurysms of the vertebral artery or PICA are seen Meningioma The most common primary neoplasm in this area Schwannoma From cranial nerves IX and XI. Neurofibromas from
ex-isting spinal nerve segments occur laterally Epidermoid tumors
Metastases Cisternal, perineural, and skull base Paragangliomas
Arachnoid, inflamma-tory and neurenteric cysts Chordomas,
rheuma-toid nodules Extraosseous intradural Posterior
extramedul-lary intradural masses Congenital or acquired
tonsillar herniation Represents 5 – 10% of all foramen magnum masses Ependymoma,
medullo-blastoma
Intra-axial caudal extension of posterior fossa neoplas-tic masses
Extradural masses
Trauma Odontoid fractures
Arthropathies
– Rheumatoid arthritis Affects 80% of cervical spine in these patients, causing severe cord compression
– Osteoarthritis – Paget’s disease – Osteomyelitis Congenital anomalies – Os odontoideum – Vertebralization of
oc-cipital condyles – Odontoid hypoplasia – Arch hypoplasias or
aplasias Neoplasms
– Primary ! Chordoma
! Osteocartilaginous tumors chondroma and chon-drosarcoma
– Metastases Hematogenous or local extensions from nasopharyn-geal or skull base tumors
AIDS: acquired immune deficiency syndrome; AVM: arteriovenous malformation; PICA: pos-terior inferior cerebellar artery.
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superior sagital sinus olfactory n. (CN I) optic n. (CN II) oculomotor n. (CN III)
trigeminal n. (CN V) abducens n. (CN VI)
glossopharyn-geal n. (CN IX) vagus n. (CN X) accessory n.
(CN XI)
jugular foramen medulla spinal subarachnoid space hypoglossal n. (CN XII)
transverse sinus sigmoid sinus
meningeal artery foramen
spino-sum pituary gland
Fig. 11 Intracranial tumors. Anatomic drawing depicting the endocranial aspect of the skull base