TUMOURS OF THE CPA

Liew Boon SengMaster of Neurosurgery

Overview• 8–10% of all intracranial neoplasms• 80–85% of CPA tumours are acoustic neuromas, with meningiomas

and a wide variety of other lesions.• The major differential diagnoses for a cerebellopontine angle

tumour, in decreasing frequency:-– Acoustic schwannomas– meningioma – metastatic tumour – exophytic brainstem glioma – epidermoid tumour.

• In most cases, MR imaging and computed tomography (CT) show typical features of acoustic neuromas or meningiomas and are sufficient to establish the diagnosis.

Intraventricular Tumours

• The foramen of Luschka provides a communication between the fourth ventricle and the CPA.

• In view of this, lesions of the ventricular system, such as ependymomas, choroid plexus tumours and dermoid tumours, may protrude into the CPA.

• Presentation may be related to cranial nerve compression, mass effect or hydrocephalus.

Acoustic Schwannomas

• Arise from the 8th cranial nerve• 8% of intracranial tumours • Schwannomas occur less frequently on the 5th cranial nerve and

rarely involve other cranial nerves. • The acoustic schwannoma takes origin from the vestibular

component of the 8th cranial nerve near the internal auditory meatus, at the transition zone where the Schwann cells replace the oligodendroglia.

• Great variations of growth rate from around 2 mm per year is usual, to as much as 17 mm per year

Clinical Presentation

• Cranial nerve dysfunction: – Unilateral hearing loss; tinnitus; dysequilibrium and vertigo; – Diplopia due to an abducens palsy; – Facial paraesthesia, anaesthesia, or pain. – Facial weakness or spasms are unusual at presentation. – Large lesions may lead to dysphonia, dysarthria and dysphagia

due to involvement of the IX and X cranial nerves.• Cerebellar and/or brainstem compression:

– Impaired co-ordination, upper motor neurone signs in the limbs.• Raised intracranial pressure secondary to associated

hydrocephalus, or occasionally to the mass of the lesion itself.• Pain localized to the ear/mastoid regions, or sometimes non-

localizing headache.

Macroscopic

• Lobulated with a capsule that separates it from the surrounding neural structures.

• Arise from within the internal auditory canal and occupy the porus of the internal auditory canal.

• As the tumour grows, the 8th nerve is destroyed and the adjacent cranial nerves become stretched around the tumour.

• As the tumour grows medially it compresses and displaces the cerebellum and distorts the brainstem.

• Large tumours will result in obstruction of the 4th ventricle and hydrocephalus.

• The superior cerebellopontine cistern is invaginated by the tumour, forming a double arachnoid plane around the lesion.

Histology• WHO Grade I• Spindle-shaped cells with hyperchromatic, elongated nuclei (Antoni A

type)• Other regions where vacuolated cells with pleomorphic nuclei are

embedded in a loose eosinophilic matrix in which microcystic change may be prominent (Antoni B).

1. The 7th nerve is typically displaced on the ventral and anterior surface of the tumour.

2. The trigeminal nerve is carried upwards and forwards by the upper pole.

3. The 6th nerve lies ventral and usually medial to the major mass

4. The lower cranial nerves are displaced around the inferior pole of the tumour

•Facial and superior vestibular nerves are above the transverse crest and the cochlear and inferior vestibularnerves are below.•Facial nerve occupies the anterosuperior quadrant of the lateral meatus.

•Facial nerve is displaced directly anteriorly•This is a frequent direction of displacement with acoustic neuroma.

•Another frequent direction of displacement of the facial nerve is anterior and superior.

•The facial nerve is displaced anteriorly and inferiorly by tumour, which erodes the superior wall of the meatus above the nerves and grows into the area above the nerves, displacing them inferiorly

From, Rhoton AL Jr: Microsurgery of the Internal Acoustic Meatus. Surg Neurol 2:311–318, 1974 [32]

Signs and Symptoms• Tinnitus and unilateral partial or complete sensorineural hearing loss

are the earliest features.

• The growth of the tumour is so slow that facial paresis is not evident until the tumour is large

• At that stage 5th nerve compression may be evident, with diminished facial sensation and a depressed corneal reflex.

• Cerebellar involvement will result in ataxia, and compression of the pyramidal tracts from a very large tumour causing brainstem compression will cause a contralateral hemiparesis

• If a large tumour has caused obstructive hydrocephalus the patient will also present with features of raised intracranial pressure.

Imaging• The CT scan or MRI will show an enhancing tumour

extending from the internal auditory canal into the cerebellopontine angle

• The internal auditory meatus will be widened

• Very small acoustic neuromas, which are predominantly within the internal auditory canal, may be more difficult to diagnose.

•The porus acousticus forming a cone-shapedmass with a canalicular and CPA componentin 61% of patients.•In 21% of cases, thecanalicular component becomes sausage-shapedand “mushrooms” out of the porus into the CPA, leading to a dumbbell appearance. •In the remainder (18%), the tumours appear to belargely confined to the CPA with no significantIntracanalicular component

(Samii and co-worker, 1995)

Treatment

2 Stereotactic Radiosurgery

3 “watch, wait and re-scan”

1

Schwannomas of the other LowerCranial Nerves

• The facial and trigeminal nerves are more frequently affected than the bulbar nerves.

• These lesions may occur entirely within the CPA but, in the case of trigeminal schwannomas, dumbbell extension through Meckel’s cave into the middle cranial fossa is usual.

• Facial nerve neuromas are usually indistinguishable from acoustic lesions until the tumour is encountered at surgery.

• Surgery is therefore performed either by the translabyrinthine or retrosigmoid approach according to the patient’s pre-operative hearing.

• Neuromas of the trigeminal nerve often present with a dumbbell mass present in both the posterior and middle cranial fossae, usually removed via a pre-sigmoid combined posterior fossa/middle fossa approach.

• Neuromas of the vagus, glossopharyngeal and spinal accessory nerve are exceedingly rare.

Cerebellopontine Angle Meningioma

• Meningiomas of the petrous face comprise around 7% of all CPA lesions.

• They present in patients aged 30–70 years and are five times more common in women.

Cerebellopontine Angle Meningioma

• Risk factors probably include previous radiotherapy, e.g. for childhood leukaemia.

• Inactivation of the NF-2 tumour suppressor gene appears to be important in the pathogenesis of sporadic meningioma in up to 60% of cases.

• Meningiomas of the CPA can arise in close proximity to the porus acousticus, or from a separate origin on the face of the petrous bone.

Clinical Presentation

• It simulate an acoustic neuroma with most patients have symptoms of vestibulocochlear nerve dysfunction.

• About 80% complain of hearing loss, with a dead ear being evident in 19%. Tinnitus (60%), impaired balance (26%), trigeminal signs (45%) and facial weakness (10%) may also occur.

• Symptoms such as ataxia due to cerebellar involvement and raised intracranial pressure, often due to hydrocephalus caused by obstruction of the 4th ventricle.

Imaging

• Imaging investigations show that the mean tumour size is 3.5 cm at the time of diagnosis

• CT scan appearance shows a tumour of slightly increased density prior to contrast; it enhances vividly and uniformly following intravenous contrast. Hyperostosis of the cranial vault

Treatment

• The treatment of choice for meningiomas is complete surgical excision of the tumour, its dural attachments and any abnormal bone.

• Complete macroscopic surgical excision is usually achieved in this group of patients

• Alternative treatments for meningiomas are not evidence based. • Stereotactic radiosurgery may be applicable in some selected

patients, however the relatively large tumour size at presentation (3.5 cm mean) against this approach in the majority of patients.

Cerebellopontine Angle Arachnoid Cysts

• Arachnoid cysts are pouchlike intraarachnoid masses of uncertain origin filled with CSF

• At neuroimaging, their attenuation and signal intensity match those of CSF almost exactly.

• These masses have smooth and rounded edges, displace neurovascular structures, and erode adjacent bone structures.

• There is no calcification or enhancement. • On T1- and T2-weighted images they can appear similar to an epidermoid

cyst. • Fluid-attenuated inversion-recovery and constructive interference in the

steady state sequences as well as diffusion-weighted imaging are helpful in making the distinction

• Rare and often present with headache and ataxia, rather than cranial nerve compression syndromes.

• If symptoms are few, observation is advocated. • However, symptomatic lesions require treatment. • This is most safely met through a wide fenestration procedure rather than

excision or shunting

Imaging

Arachnoid cyst in a 27-year-old woman with headaches. (a) Axial T1-weighted MR image shows an arachnoid cyst with signal intensity similar

to that of CSF stretching the left seventh and eighth cranial nerve complex (arrow).(b) Axial T2-weighted MR image shows the cyst displacing the vascular structures of

the CPA (arrowheads).

Melanocytic Neoplasms• Melanocytes are normally present in the intracranial leptomeninges,

usually in the posterior cerebral fossa, and can give rise to benign (meningeal melanocytoma) or malignant (malignant melanoma) tumours.

• However, metastatic malignant melanomas greatly outnumber primary melanocytic neoplasms.

• At CT, primary melanocytic lesions appear as well-circumscribed, isoattenuating to hyperattenuating extraaxial tumours with homogeneous enhancement.

• Even if there is no hyperostosis, they can mimic a meningioma. • MR imaging demonstrates variable signal intensity on T1- and T2-

weighted images in proportion to the amount of melanin within the tumo.

• Therefore, melanocytic neoplasms are isointense or hyperintense to adjacent normal brain tissue on T1-weighted images and isointense or hypointense on T2-weighted images.

• They enhance after intravenous administration of contrast material.

Imaging

Melanoma in a 58-year-old woman with a left cerebellar syndrome. (a) Axial CT scan shows a hyperattenuating melanoma of the left CPA.(b) Axial T1-weighted MR image shows a well-defined extraaxial mass at the posterior edge of thepetrous bone. The high signal intensity is suggestive of melanin. (c) Gadolinium-enhanced axial T1-weighted MR image shows a normal left internal auditory canal (arrow) and lack of dural tail enhancemen

Others meningeal lesions

• In addition to carcinomatous meningitis, many infectious or inflammatory diseases can have focal nodular meningeal involvement and manifest as a CPA mass.

• Leptomeningeal metastases from lung cancer, breast cancer, melanoma, or other neoplasms can mimic benign tumours of the CPA.

• Therefore, when an unusual aggressive schwannoma-like mass is encountered and no primary cancer is known to be present, radiologists should be aware of the possibility of metastases and check the lungs and breast carefully.

Metastases in a 67-year-old man with lung cancer and right-sided hypoacusia, vertigo, and ear pain.

(a) Axial T2-weighted MR image shows a metastasis of the right CPA that mimics a vestibular schwannoma but with unusual associated middle ear retention.

(b) Contrast-enhanced axial T1-weighted MR image shows intense enhancement of the lesion, which extends into the cochlea (arrow). Note the presence of another enhancing lesion at the tip of the right petrous bone (arrowhead).

Others meningeal lesions

• However, in most cases, there are numerous other intra and extraaxial masses, which are very suggestive of metastases when correlated with a clinical history of carcinoma.

• Tuberculosis is one of the main causes of focal pachymeningeal thickening in the posterior cranial fossa, but this finding is not specific.

• Neurosarcoidosis can also appear as a dura-based mass, like meningioma. The lesions of neurosarcoidosis are hyperattenuating on CT scans and isointense to gray matter on T1-weighted images with homogeneous enhancement; however, the possible low signal intensity on T2-weighted images may suggest the diagnosis.

Epidermoid Tumour(Cholesteatomas)

• Primary epidermoid tumours (cholesteatomas), are non-neoplastic, cystic lesions lined with a simple stratified squamous epithelium.

• They are considered to be congenital, arising from misplaced epidermal cell rests

• Cholesteatomas of the CPA must be differentiated from the acquired lesions that occur secondary to middle-ear suppurative disease.

• Acquired lesion are usually restricted to the tympano–mastoid region, but erosion of the petrous bone may occur, with the appearance of a petrous apex cholesteatoma.

• CPA cholesteatomas present in adults of either sex with a mean age of 43 years.

• They contain lamellae of desquamated keratin, cell debris and a variable number of cholesterol crystals.

• Macroscopically, the lesions resemble clusters of pearls. • They grow slowly, by a process of desquamation, and infiltrate the

cisternal spaces. • Cranial nerve palsies dominate the clinical presentation

Imaging

Epidermoid cyst in a 52-year-old woman with epilepsy. (a) Axial T1-weighted MR image shows an epidermoid cyst with characteristic focal marbling in the left

CPA (arrow).(b) Axial T2-weighted MR image shows the lobulated margins of the cyst impinging on the pons

(arrowhead).(c) Axial heavily T2-weighted (constructive interference in the steady state) MR image shows the

extentof the tumour.

Treatment• The surgical approach is determined by the clinical presentation.• If hearing is preserved, a retrosigmoid approach is favored whereas

a transpetrous approach is used if useful hearing has been lost pre-operatively

• If the lesion extends far medially, the cochlea may require removal to provide sufficient access.

• Cholesteatomas usually envelop a multitude of cranial nerves and vascular structures.

• While the soft contents of the lesion can readily be removed, the capsule, which is usually adherent to vascular and neural structures, needs to be excised to avoid recurrence.

• Although the mortality from surgery to remove these lesions is low, neurological morbidity in the form of post-operative cranial nerve lesions is frequent.

• This is most commonly the facial nerve, and is most frequently confined to a House–Brackmann Grade II weakness, but complete lesions can occur.

• Lower cranial nerve lesions were also present in around 30–40%.

Grade Function Description

1 Normal Normal function in all areas

2 Mild dysfunction Slight weakness on close inspection

3 Moderate dysfunction Obvious but not dysfiguring

4 Moderate-severe dysfunction

Obvious weakness and/or dysfiguring and assymetry

5 Severe dysfunction Barely perceptible motion

6 Total paralysis No movement

House-Brackmann Grade (Facial Nerve Palsy)

Dermoid Cysts

• Like epidermoid cysts, dermoid cysts result from inclusion of ectodermal elements during neural tube closure but may originate a bit earlier.

• Dermoid cysts are midline lesions that rarely invade the CPA laterally and contain elements from all layers of the skin.

• Thus, fat, hair, sebaceous glands, and sweat glands can be found in addition to squamous epithelium.

• Typically, dermoid cysts have negative attenuation values on CT scans and high signal intensity on T1-weighted images due to their fatty content, may have a very suggestive fat-fluid level, and contain calcifications.

Lipoma• Lipomas in the CPA are maldevelopmental masses that arise from

abnormal differentiation of the meninx primitiva. • They are homogeneous fatty lesions surrounding and encasing

normal adjacent neurovascular structures with very dense adhesions.

• Nevertheless, lipomas are rarely symptomatic, and conservative follow-up is often preferred to aggressive and potentially risky resection.

• Lipomas appear as fat: homogeneously hypoattenuating with a negative attenuation value on CT scans and as characteristic and suggestive homogeneous high signal intensity on T1-weighted images, which decreases on fat-suppressed images.

• There is no enhancement after contrast material administration. Therefore, nonenhanced T1-weighted imaging should be performed when evaluating a CPA syndrome to look for spontaneous hyperintense lesions, such as lipomas.

Imaging

Lipoma in a 7-year-old boy with a polymalformation syndrome. (a) Axial CT scan shows a welldefined hypoattenuating lipoma of the left CPA. (b) Axial T1-weighted MR image shows that the lipoma has signal intensity similar to that of subcutaneous fat.

Pedunculated Brainstem Glioma• In young adults, brainstem gliomas can manifest as asymmetric

expansion of the brainstem with a possible pedicle into the CPA and even then can mimic an acoustic neuroma.

• Gliomas appear as hypoattenuating masses at CT with variable enhancement depending on the glioma grade.

• At MR imaging, T1-weighted images show hypointense masses, whereas T2- weighted images show hyperintense tumours as well as hyperintense adjacent edema.

• In addition, the exophytic component in the cerebellopontine cistern is much better demonstrated than at CT.

Imaging

Brainstem glioma in a 23-year-old man with vertigo and hypoacusia. Contrast-enhanced axial T1-weighted MR image shows an unusual round gradeIII glioma located in front of the porus. The tumour demonstrates central enhancement.

Choroid Plexus Papilloma• Choroid plexus papillomas occur mainly in children but also occur in

adults. • These tumours derive from the neuroepithelial cells of the choroid

plexus and recapitulate the structure of normal choroid plexus when benign.

• Therefore, papillomas can be encountered wherever choroid plexus is.

• In adults, choroid plexus papillomas often arise in the fourth ventricle and extend to the CPA through the foramen of Luschka, but they can also primarily develop in the CPA.

• At CT, these tumours are frequently hyperattenuating on nonenhanced scans with a possible cyst and calcification.

• MR imaging shows an isointense, irregular, but homogeneous mass that strongly enhances after injection of gadolinium contrast material and is often associated with hydrocephalus.

• The hydrocephalus is explained in part by CSF hypersecretion by the tumour.

• There is usually no edema in the brainstem and no erosion of adjacent bony structures.

Lymphoma• Lymphomas can be observed in the posterior cranial fossa and

even partly in the CPA. • Lymphomas appear as isoattenuating or hyperattenuating

homogeneous masses on CT scans with intense enhancement after contrast agent administration.

• At MR imaging, lymphomas invading the CPA have no specific imaging features;– they are hypointense on T1-weighted images and hyperintense on T2-

weighted images and enhance after contrast agent injection. • Nevertheless, mass effect and edema are also present and may

suggest the intraaxial origin and therefore the correct diagnosis, especially in an immunodeficient patient.

Imaging

Lymphoma in a 34-year-old man with acquired immunodeficiency syndrome, vertigo, and headaches.

(a) Contrast-enhanced axial T1-weighted MR image shows a round lymphoma mimicking a vestibular schwannoma in front of the right porus.

(b) Axial T2-weighted MR image shows narrowing of the cisterns and extensive edema, which suggest an intraaxial tumour.

Hemangioblastoma• Hemangioblastomas are frequent in von Hippel– Lindau disease,

but they may also occur in the absence of that disease in the posterior cranial fossa of young adults, where they rarely reach the cerebellar surface and invade the CPA.

• Hemangioblastoma usually appears as a large, well-circumscribed, homogeneous cystic mass with a small hypervascular mural nodule, but it can also appear as a solid mass without a cystic component.

• The nodule appears hypointense on T1-weighted images and hyperintense on T2-weighted images and enhances intensely after injection of gadolinium contrast material.

• Because of the hypervascularity, possible high-flow vessels can be observed as flow voids at the periphery of the mass.

• When present, cysts usually have smooth margins and homogeneous CSF-like signal intensity.

• Finally, edema is usually slight or absent around this intraaxial tumour.

Imaging

Hemangioblastoma in a 28-year-old woman with von Hippel–Lindau disease and vertigo.(a) Axial T2-weighted MR image shows a solid hemangioblastoma in the left CPA. Note the

vascular pedicle (arrowhead), which appears as a flow void with all sequences. (b) Contrast-enhanced axial T1-weighted MR image shows homogeneous enhancement of the

hemangioblastoma (arrowhead). (c) Contrast-enhanced sagittal MR image shows a spotty, solid intraaxial hemangioblastoma

(arrow) beneath the first one.

Ependymoma• Ependymomas of the posterior cranial fossa are more frequent in

children but can also occur in young adults. • Such lesions usually arise in the fourth ventricle and its lateral

recesses and may extend into the CPA by means of an exophytic component.

• However, an extraaxial origin directly in the CPA is also possible.• Ependymomas appear as irregular, lobulated tumours that can

invade the cerebellar parenchyma.• They are hypointense on T1-weighted images and hyperintense on

T2-weighted images and demonstrate irregular enhancement. • Ependymomas are markedly heterogeneous due to calcification,

hemorrhage, cystic components, or necrosis

Imaging

Ependymoma in a 24-year-old woman with vertigo, headaches, and left facial nerve palsy. (a) Contrast-enhanced axial T1-weighted MR image shows a heterogeneous ependymoma

with a lobulated multicystic component in the left CPA. The tumour invades the internal auditory canal without widening the porus (arrow).

(b) Coronal T2-weighted MR image shows marked mass effect of the ependymoma on the brainstem.

Medulloblastoma• Adult cerebellar medulloblastomas mostly occur during the 3rd or

4th decade of life. • They appear as round or ovoid tumours with smooth margins, are

more common in the cerebellar hemisphere than in the vermis, and often extend to the brain surface with possible exophytic invasion of the CPA or internal auditory canal.

• Irregularity of some portions of the tumour-brain interface is a clue to their intraaxial origin.

• At nonenhanced CT, medulloblastomas are frequently hyperattenuating and uncommonly demonstrate calcification.

• At MR imaging, these tumours are hypointense on T1-weighted images and iso- or hyperintense on T2-weighted images with possible cystic or necrotic components and enhance after injection of gadolinium contrast material

DysembryoplasticNeuroepithelial tumour

• Dysembryoplastic neuroepithelial tumours arise from dysembryoplastic cortex, yet have rarely been reported in the posterior cranial fossa.

• When such tumours occur in this location, the patients tend to be young adults with minor symptoms such as headache, vertigo, or tinnitus for several years but without seizures.

• MR imaging shows a large, heterogeneous, slow-growing lesion with a predominant cystic component and an enhancing mural nodule of hamartomatous tissue.

• Mass effect is less significant than would be expected, and no edema is seen in the brainstem. Erosion of adjacent bony structures is suggestive of dysembryoplastic neuroepithelial tumour when associated with a large cystic lesion of the CPA that manifests as mild, long-lasting symptoms.

Imaging

Dysembryoplastic neuroepithelial tumour in a 39-year-old man with mild, longlastingheadaches. (a) Axial T2-weighted MR image shows a large dysembryoplastic neuroepithelial tumour of the

right CPA with a cystic component () associated with a possibly suggestive bone erosion (arrow). Note the lack of edema.

(b) Contrast-enhanced axial T1-weighted MR image shows enhancing hamartomatous tissue (*) and possibly suggestive slight mass effect with a normal left cerebellopontine cistern (arrow).

Imaging

Choroid plexus papilloma in a 49-year-old woman with vertigo and intracranial hypertension.(a) Axial T2-weighted MR image shows a right CPA papilloma extending through theforamen of Luschka. The tumour contains massive hypointense calcification (arrowhead). (b) Contrast- enhanced axial T1-weighted MR image shows intense enhancement of the hypervascularized tumour. Note the normal choroid plexus in the left foramen of Luschka.

Cholesterol Granuloma• Cholesterol granulomas can occur in any obstructed air cells. • They often arise from the apex of the petrous bone and may enlarge

enough to expand in the posterior cranial fossa and produce nerve disturbances.

• At CT, cholesterol granulomas appear as sharply and smoothly marginated expansile lesions in the temporal bone, isoattenuating with brain tissue and nonenhancing.

• At MR imaging, they characteristically have a large central region of increased signal intensity and a thin peripheral rim of decreased signal intensity on both T1- and T2-weighted images. The latter finding corresponds to expanded cortical bone and hemosiderin deposits.

• Spontaneous and homogeneous central high signal intensity on T1- weighted images is very suggestive of a cholesterol granuloma.

Imaging

Cholesterol granuloma in a 32-yearold man with right trigeminal neuralgia. (a) Axial T1-weighted MR image shows a cholesterol granuloma at the apex of the right petrous bone

with typical high signal intensity. An additional suggestive feature is the thin hypointense rim (arrowheads), which represents expanded cortical bone of the petrous apex.

(b) Axial T2-weighted MR image shows that the granuloma has heterogeneous signal intensity surrounded by a hypointense rim (arrowheads).

(c) Contrast-enhanced coronal T1-weighted MR image shows the normal right trigeminal nerve (arrow) at the top of the mass.

Glomus Tumours• Glomus tumours result from neoplastic transformation in

paraganglionic “jugular bodies”.• Since spread of these tumours follows the path of least resistance,

large tumours may present within the CPA. • Glomus tumours are slow-growing in nature and often large before

become clinically evident (average 3-6 years from first symptom to diagnosis)

• The presenting symptoms include hearing loss, pulsatile tinnitus, dysequilibrium, dysphonia, dysphagia and aural bleeding.

Classification

Treatment• Surgical excision offers a potential cure in the treatment of these

patients. • A combined trans and infratemporal approach to Type C

(tympanomastoid with infralabyrinthine or petrous apex destruction) and D (intradural extension) tumours as described by Fisch.

• Pre-operative angiography with tumour embolization, where possible, is mandatory. Preliminary control of the internal carotid artery, the sigmoid sinus and the cavernous sinus is necessary to avoid a vascular catastrophe.

• 70% of patients had an “excellent”, 10% a “good” and 20% a “poor” outcome from surgery for large glomus tumours.

• Long-term follow-up has shown that a small number of patients may develop local tumour recurrence.

• Early post-operative MRI needed to assess residual disease and provide a baseline for future reference.

• If tumour recurrence occurs, further surgery and/or radiotherapy needs to be considered.

Chondroma and Chondrosarcoma

• Chondromatous tumours develop from embryonic cartilaginous remnants enclosed in the bones of the skull base.

• They often arise from the petrooccipital or sphenooccipital synchondrosis and destroy the adjacent bones.

• Chondromatous tumours can be hypoattenuating at CT, possibly with a marginal high-attenuation area due to a dense matrix of hyaline cartilage or massive calcification.

• Lytic bone erosion may be seen.• At MR imaging, the tumour is hypointense on T1-weighted images

and heterogeneously hyperintense on T2-weighted images; it enhances poorly due to its hypovascularity

Imaging

Chondrosarcoma in a 25-year-old woman with intracranial hypertension. (a) Axial T2-weighted MR image shows a well-defined chondrosarcoma with marked mass effect

on the pons and fourth ventricle. (b) Axial T1-weighted MR image shows a skull base pedicle. (c) Contrast-enhanced coronal T1-weighted MR image shows punctate enhancement, which

could suggest a chondromatous lesion. (d) Axial CT scan shows an eroded petro-occipital synchondrosis, which reflects the cartilaginous

origin of the chondrosarcoma, although no calcifications are seen.(*)

Chordoma

• Chordomas develop from remnants of the notochord and are located near the dorsum sellae, from which they can expand into the CPA.

• At CT, chordomas appear hypoattenuating with possible slight calcification at the periphery of the tumour in association with irregular bone erosion.

• At MR imaging, especially on T2-weighted images, chordomas usually appear as lobulated, large, hyperintense masses with septa of low signal intensity.

• Slight enhancement is present. • The overall appearance can be quite similar to that of chondroma.

Imaging

Chordoma in a 61-year-old man with left trigeminal neuralgia and headaches. Contrast-enhanced axial T1-weighted MR image shows a chordoma invading the left CPA with unusual sparing of the clivus. There are suggestive enhanced septa (arrowheads).

Endolymphatic Sac Tumour• Endolymphatic sac tumours are papillary adenomatous tumours that

originate from the endolymphatic sac, which is located in the distal portion of the vestibular aqueduct of the petrous bone.

• These tumours occur sporadically but are frequent in von Hippel–Lindau disease.

• At CT, the tumour destroys the retrolabyrinthine petrous bone with geographic or moth-eaten margins, and intratumoural spiculated or reticulated bone can be seen.

• At MR imaging, endolymphatic sac tumours appear heterogeneous on both T1- and T2-weighted images with focal high signal intensity due to subacute hemorrhages and low signal intensity due to calcification or hemosiderin.

• Blood-filled cysts and protein-filled cysts, both of which appear hyperintense on T1- and T2-weighted images, may be present and suggest the diagnosis.

• Heterogeneous enhancement is seen after contrast material administration.

Imaging

Endolymphatic sac tumour in a 26-year-old woman with von Hippel–Lindau disease and vertigo.

(a) Contrast-enhanced axial T1-weighted MR image shows an endolymphatic sac tumour that destroys the right temporal bone and invades the CPA with hyperintense blood and a protein-filled cyst.

(b) Axial T2-weighted MR image shows the cystic component of the tumour more clearly.(*)

Pituitary Adenoma

• Rarely, aggressive and invasive pituitary macroadenomas can destroy the dorsum sellae, extend behind the clivus, and invade the CPA laterally.

• Invasive pituitary adenomas appear as enhancing soft-tissue masses centered around the pituitary fossa, which erode adjacent bony structures and invade surrounding normal structures.

• Rare metastases from pituitary adenoma can also be encountered in the CPA.

• In both situations, a history of pituitary adenoma may be present and is helpful in making the diagnosis.

Apex Petrositis• Apex petrositis (petrous apicitis) involves an inflammatory lesion of

the petrous apex secondary to otitis media. • In addition to ear pain, patients experience fifth and sixth cranial

nerve palsy; this clinical complex constitutes Gradenigo syndrome. • CT scans show a destructive lesion of the petrous apex, often in

association with fluid in the middle ear. MR imaging can show an enhancing mass at the petrous tip and extension of this mass, as well as its relationship to cranial nerves V and VI

Imaging

Apex petrositis in a 50-year-old woman with Gradenigo syndrome at clinical evaluation.(a) Axial T1-weighted MR image shows an irregular lesion at the tip of the petrous apex (arrow).(b) Contrast-enhanced axial T1-weighted MR image shows right-sided apex petrositis as anenhancing lesion along the courses of cranial nerves V and VI (arrow).

Basilar Artery Ectasia and posterior circulation aneurysms

• The vertebral and basilar arteries and some of their branches pass through the cerebellopontine cistern, where a tortuous segment or ectasia or even an aneurysm can develop, present as a mass in the CPA.

• Although not neoplasms, such lesions can cause mass effect on the neural structures of the CPA and thus produce neurologic symptoms

• These lesions should be recognized at a stage that enables appropriate neurovascular management to be directed at them.

• High-flow aneurysms appear as oval or round masses that have no signal (flow void) with all spin-echo sequences.

• Extreme low signal intensity on T2-weighted images is very suggestive of such lesions and indicates that normal arteries need to be evaluated.

• When an aneurysm is thrombosed, high signal intensity on T1-weighted images due to methemoglobin could be suggestive, but the signal intensity is variable; radiologists should be aware that enhancement of the mass can be observed due to organization of the thrombus, thus mimicking a schwannoma

Imaging

Asymptomatic aneurysm in a 68-year-old man with lymphoma and right trigeminal neuralgia. a) Axial T2-weighted MR image shows an aneurysm of the left posterior inferior cerebellar artery with typical lack of signal (arrow). Note the lymphoma in the right pterygopalatine fossa (arrowheads),which explains the neuralgia.

Aneurysm in a 75-year-old man with hypoglossal nerve palsy.b) Axial T2-weighted MR image shows a thrombosed aneurysm of the right posterior inferior cerebellarartery with focal calcification (arrowhead). Note the normal right hypoglossal canal (arrow), a finding inconsistent with a schwannoma. c) Contrast- enhanced coronal T1-weighted MR image shows homogeneous enhancement of the organized thrombus, which completely fills the aneurysm.

Conclusion• MRI scans can usually provide the surgeon with an accurate pre-

treatment diagnosis for lesions in the CPA.• Acoustic neuromas are relatively common neoplasms of the CPA. • Surgical approaches are well described, and the treatment

outcomes, namely complete tumour removal with minimum mortality and morbidity, well established.

• Microsurgical excision, stereotactic radiosurgery and a “watch, wait and re-scan” policy all have merits in different patients with CPA lesions.

• Other tumours of the CPA are very rare. These tumours may have very complex relationships with cranial nerves, blood vessels and the skull base.

• While surgery remains the mainstay in the treatment of all of these lesions, technical difficulties always presence.

• Extended routes of access are frequently used to achieve maximal excision with minimal morbidity.

Conclusion• Considerable experience at treating CPA acoustic neuromas is

therefore highly desirable before embarking upon surgery for CPA rarities.

• Due to the large number of problems that these patients may present, a multi-faceted-team approach is advocated at all stages of treatment.

• In view of the rarity of these tumours, a tertiary referral system to allow patients to benefit from the pooling of both experience and resources.

Thank You