Ciprian Gradinaru MD, Mark Kelly MD Brent Griffith MD, Suresh Patel MD

Division of NeuroradiologyHenry Ford Health System

Disclosures

None of the authors have any disclosures

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• The skull base anatomy can be divided into the anterior, middle and posterior compartments

• Tumors can arise from skull base structures or extend into the skull base region from intra or extra cranial lesions

• Skull base tumors offer a number of unique challenges:• Deep location

• Complex anatomy (neurovascular foramina, adjacent structures)

• Close proximity to eloquent structures (brain, orbit, CN’s, vessels)

• Diverse pathology (benign/malignant tumors, infectious, congenital)

• The osseous skull base and pachymeninges (dura mater) are effective barriers, but tumor can spread through skull base foramina

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• Lesion evaluation• Anatomic localization

• Extent of disease

• Pattern of growth (benign vs. aggressive)

• Imaging characteristics

• Prognostic information• Disease staging

• Morbidity and mortality

• Treatment planning• Biopsy/surgical approach

• Need for adjuvant therapy

• Treatment Follow-up• Treatment response and effects

• Recurrence and progression of disease

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CT

•Can be performed quickly

•Excellent anatomic detail of osseous structures

•Information regarding lesion aggressiveness (smooth remodeling vs. erosion of adjacent bone)

•Multi-planar reconstructions in any imaging plane from single acquisition

•Requires ionizing radiation

MR

•Longer scan times.

•Excellent evaluation of soft tissues

•Involvement of neurovascular structures.

•Need multiple imaging pulse sequences for characterization of lesions

•Prone to artifact (especially at skull base)

•No radiation

CT and MR play a complimentary role.

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Anatomic Location

•The skull base is generally grouped into anterior, middle, and the posterior cranial fossae

•Location-based classification is helpful because:

• Regional specificity of certain tumor types

• Similar clinical findings

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Anterior Cranial Fossa

•Cancers of the paranasal sinuses or nasal cavity are the most common malignant tumors

•Tumor examples:• Meningioma• Esthesioneuroblastoma• Sino-nasal (SN) malignancies• Giant cell tumor (GCT)• Hemangiopericytoma• Multiple myeloma (MM)/plasmacytoma• Sarcomas (Osteo. and Rhabdo.) • Lymphoma• Melanoma

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Middle Cranial Fossa

•Central region:• Pituitary adenoma, meningioma, pseudotumor, craniopharyngioma, sphenoid sinus carcinoma

•Clival region:• Chordoma, meningioma, paraganglioma, naso-pharyngeal (NP) carcinoma, schwannoma, chondrosarcoma, MM/plasmacytoma, pseudotumor

•Para-central/Cavernous Sinus region:• Meningioma, schwannoma, adenoid cystic carcinoma (ACC), NP carcinoma, GCT, pseudotumor

•Petro-Clival/Lateral region:• Meningioma, schwannoma, NP angiofibroma, ACC, sarcoma, acquired/congenital cholesteatoma, cholesterol granuloma, pseudotumor

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Posterior Cranial Fossa

•Cerebellopontine (CP) angle: • Schwannoma, meningioma, epidermoid,

arachnoid cyst, cholesterol granuloma, endo-lymphatic sac tumor, metastasis, leptomeningeal and granulomatous process

•Jugular foramen: • Paraganglioma, schwannoma, meningioma,

metastasis

•Foramen magnum: •Meningioma, schwannoma, chordoma, intra-medullary cord tumor, neurenteric cyst

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Behavior – Benign or Aggressive?•Osseous changes

• CT smooth remodeling vs. permeative/destructive pattern

• MR bone marrow involvement (T1 signal abnormality)

Smooth Remodeling (Pituitary Macro-adenoma)

Permeative/Destructive(Sarcoma)

T1 Marrow Replacement(NP Carcinoma)

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Behavior – Benign or Aggressive?•Osseous changes

•Tumor cellularity (high)• T2WI hypo to iso-intense signal compared to gray matter

• DWI/ADC restricted diffusion

Restricted Diffusion(Meningioma)

Iso-intense T2 signal(Esthesioneuroblastoma)

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Behavior – Benign or Aggressive? •Osseous changes

•Tumor cellularity

•Intra-lesion contents (hemorrhagic or necrotic components)•T1WI pre hyper-intense signal (hemorrhage)

•T1WI post non-enhancing necrotic tissue

Central Necrosis(Chondrosarcoma)

T1 Pre T1 Post

Hemorrhage(Chondroblastoma)

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Behavior – Benign vs. Aggressive?

•Osseous changes

•Tumor cellularity

•Intra-lesion contents

•Tumor margins• MRI best on T2wi and post T1wi

• Well-defined/smooth Benign

• Ill-defined/infiltrative Aggressive

Well-defined (Meningioma)

Ill-defined (AdenoCa)

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Extension•Extra-cranial vs. Intra-cranial

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SN Neuroendocrine Carcinoma (SNEC) Meningioma

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Extension•Extra-cranial vs. Intra-cranial

•Direct vs. Indirect (perineural)

• Skull base bone and pachymeninges (dura mater) act as barrier

• Neurovascular foramina and cranial nerves provide conduit

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http://www.imaios.com/Media/Images/e-anatomy/Cranial-nerves-anatomy-diagrams/skull-cranial-base-foramen-cranial-nerves-anatomy-en

Extension•Perineural involvement includes perineural invasion and spread

• Perineural invasion microscopic feature of malignancy is often confined to the main tumor mass

• Perineural spread clinico-radiologic observation of distant spread of tumor via perineural spaces or within the nerve sheath/nerve itself

•Most often seen with extra-cranial squamous cell carcinoma

•Most commonly seen with salivary gland tumors (mainly ACC and Muco-epidermoid carcinoma)

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Extension

Imaging of Peri-neural Involvement

• Focal/segmental/diffuse enhancement and enlargement of the cranial nerve

• Skull base foramen enlargement and replacement of the normal fat within the foramen

• Look for denervation atrophy of the muscles supplied by the involved cranial nerve

Heterogeneously enhancing mass of the left parotid gland (Mucoepidermoid Carcinoma) with enlargement and enhancement of the left facial nerve as it enters the stylomastoid foramen (normal right facial nerve)

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Integrity of Eloquent Structures•Dural, leptomeningeal and parenchymal invasion

• T1WI (post-contrast) and T2WI/FLAIR are best

• Leptomeningeal or dural enhancement (nodular or linear > 5 mm)

• Enhancement or edema of brain adjacent to tumor

SN Poorly Differentiated Adenocarcinoma

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Integrity of Eloquent Structures•Dural, leptomeningeal and parenchymal invasion

•Skull base foramina and contents

• Foraminal anatomy is key

• MRI Loss of normal fat and enhancement within neuroforamina

• CT Helpful for evaluation of osseous walls of neuroforamina

Left cavernous sinus meningioma spreading into the left masticator space via the left foramen ovale and into the left pterygopalatine fossa via the left foramen rotundum

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Integrity of Eloquent Structures•Dural, leptomeningeal and parenchymal invasion

•Skull base foramina and contents

•Orbit and optic nerve

• Orbital fissures and apex are most commonly involved• Periorbital and CN-II dural sheath closely related at orbital apex

Lymphoma encasing left optic nerve

Meningioma invading the left orbital apex

Enhancing soft tissue replacing fat within a widened right superior orbital fissure

(Meningioma)

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Integrity of Eloquent Structures•Dural/Parenchymal invasion

•Skull base foramina and contents

•Orbit and optic nerve

•Cavernous sinus (CS) involvement

• Loss of normal CS enhancement

• Convex bulging of the lateral wall of the CS (normally concave)

Nasopharyngeal SCC

Invasive Pituitary Macroadenoma

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Location• Floor of the anterior cranial fossa

Behavior • Hyperostosis of adjacent skull base

(non-aggressive)

• Hyperdense mass (indicates high cellularity, but not behavior)

Extension• Intact skull base without evidence

of extra-cranial extension

Eloquent Structures • Compression of the bilateral frontal

lobes with vasogenic edema

• Effacement of the frontal horn of the right lateral ventricle

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Location• Floor of the anterior cranial fossa

Behavior • Homogeneous enhancement

• Restricted diffusion (indicates high cellularity, but not behavior)

Extension• Intact skull base without evidence of

extra-cranial extension

Eloquent Structures • Compression of the bilateral frontal

lobes

• Displacement of vessels

Location• Tumor is centered in the superior

olfactory recess region

Behavior • Homogeneous solid enhancement

• Destroys the cribriform plate, bilateral ethmoid air cells, nasal septum as well as the bilateral superior and middle nasal conchae

Extension• Tumor extends into the floor of the

anterior cranial fossa

• Post obstructive changes in the left frontal sinus

Eloquent Structures • Slight mass effect on the bilateral

infero-medial frontal lobes

• Preserved medial orbital walls

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Location• Large mass centered in sinonasal cavity

Behavior • Poorly defined tumor margins

• Destruction of the cribriform plate, bilateral medial orbital walls, nasal cavity, ethmoid air cells and maxillary sinuses

Extension• Tumor extends into the infero-medial

anterior cranial fossa, bilateral medial orbits and bilateral maxillary sinuses

Eloquent Structures • Compression of the bilateral infero-medial

frontal lobes with vasogenic edema

• Mass effect on the bilateral medial rectus muscles

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T1 Post

T1 Pre

T2 FS

Location• Large mass centered in sinonasal cavity

Behavior • Heterogeneous enhancement

• Irregular tumor margin

Extension• Superior extension into the anterior

cranial fossa

• Extends into bilateral medial orbits and maxillary sinuses

Eloquent Structures • Compression of bilateral frontal lobes

with vasogenic edema

• Mass effect on medial rectus muscles

• Mass effect on optic chiasm

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Location• Large mass (> 10mm) centered in the

central/para-central middle cranial fossa

Behavior • Homogeneous avid enhancement

• Smooth well defined margins

Extension• Left cavernous sinus with convex lateral bulge

• Supra-sellar region

Eloquent Structures • Encasement of the left internal carotid artery

• Mass effect on the optic chiasm

• Mass effect on anteromedial left temporal lobe

• Slight flattening of the left anterior pons

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Location• Midline mass originating from the clivus

Behavior • Infiltrative mass with irregular margins

• Bony destruction

Extension• Anteriorly into sphenoid sinuses,

ethmoid air cells, and nasal cavity

• Posteriorly into pre-pontine cistern

• Superorly into sellar/supra-sellar region

• Inferiorly into nasopharynx

• Left lateral into medial middle cranial fossa and left maxillary sinus

Eloquent Structures• Mass effect on antero-medial left

temporal lobe

• Slight flattening of anterior pons

• Mass effect on pituitary gland

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Location• Midline mass originating from the clivus

Behavior • Infiltrative mass with irregular margins

(aggressive)

Extension• Anteriorly into sphenoid sinuses,

ethmoid air cells, and nasal cavity

• Posteriorly into pre-pontine cistern

• Superorly into sellar/suprasellar region

• Inferiorly into nasopharynx

• Left lateral into middle cranial fossa

Eloquent Structures• Mass effect on medial left temporal lobe

• Slight flattening of the anterior pons

• Mass effect on the pituitary gland

Location• Mass located in the right para-central

middle cranial fossa

Behavior • Homogeneously enhancing mass

• Smooth widening of the right superior and inferior orbital fissures (non-aggressive)

• Hyperostosis of the greater wing of the right sphenoid bone (non-aggressive)

Extension• Right orbital apex

• Right superior and inferior orbital fissures

• Right pterygopalatine fossa

Eloquent Structures • Neurovascular structures involving right

cavernous sinus, superior orbital fissure and pterygopalatine fossa

• Compression of optic nerve at orbital apex

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Location• Mass located in the right para-central

middle cranial fossa

Behavior • Homogeneously enhancing mass with

smooth margins (non-aggressive)

• Widening of right pterygomaxillary fissure

Extension• Right pterygopalatine fossa (replacement

of fat on precontrast T1)

Eloquent Structures • Encasement and narrowing of the right

internal carotid artery

• Slight compression of the medial right temporal lobe

• Other neurovascular structures within the cavernous sinus and pterygopalatine fossa

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Location• Soft tissue density involving the left

pterygopalatine fossa

Behavior • Intense FDG uptake on PET

• Widening of the left sphenopalatine foramen and left pterygomaxillary fissure

• Bony erosion (aggressive) of posterior left maxillary sinus wall and left pterygoid plate

Extension• Left inferior orbital fissure

• Left pterygopalatine fossa (replacement of fat on CT)

Eloquent Structures • Neurovascular structures within the left

pterygopalatine fossa and inferior orbital fissure

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Location• Lesion centered at the left petro-occipital

fissure

Behavior • Permeative osseous destruction of the

clivus and left petrous apex (aggressive)

Extension• Erosion of the wall of the left carotid

canal

• Anterior aspect of the left jugular foramen

Eloquent Structures • Potential involvement of left internal

carotid artery

• Neurovascular structures within the left jugular foramen

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Location• Mass centered at the left petro-occipital

fissure

Behavior • Heterogeneous enhancement with

areas of central necrosis

Extension• Involvement of the clivus and left

petrous apex

• Extension into the left pre-pontine and cerebello-pontine cisterns

Eloquent Structures • Compression of the pons

• Close proximity to the basilar artery

• Focal encasement of the left internal carotid artery

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Location• Mass centered within the region of the

left jugular foramen

Behavior • Moth-eaten bony destruction

(aggressive) of the left jugular foramen walls and posteromedial aspect of the left middle ear cavity

Extension• Posteromedial aspect of the left

middle ear cavity

Eloquent Structures • Neurovascular structures coursing

within the left jugular foramen (pars nervosa and pars vascularis)

• Left middle ear structures

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Location• Mass centered within the region of

the left jugular foramen

Behavior • Heterogeneous enhancement

Extension• Left jugular foramen (pars nervosa

and pars vascularis)

• Left sigmoid sinus

Eloquent Structures • Neurovascular structures within the

left jugular foramen (pars nervosa and pars vascularis)

• Left sigmoid sinus

• Left middle ear structures

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Location• Mass in the posterolateral aspect of the

left petrous temporal bone

Behavior • Partially cystic mass with enhancement of

the non-cystic component

• No restriction diffusion

• Erosive changes of the posterior left petrous temporal bone (aggressive)

Extension• Left cerebello-pontine cistern

• Left vestibular aqueduct is not identified

Eloquent Structures• Slight mass effect on the left cerebellum

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• Large variety of pathology histological diagnosis by imaging is not possible.

• Imaging plays important role in evaluation:• Anatomic localization and extent of disease

• Biologic behavior (benign vs. aggressive)

• Involvement of adjacent eloquent structures

• Treatment planning (3-D surgical navigation)

• Post-treatment morbidity and mortality

• Follow-up post-treatment

• Complex anatomy and diverse pathology• Systematic approach for evaluating skull base tumors is important

• Location and behavior can help shorten the differential diagnosis

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1.Erdem E et al: Comprehensive review of intracranial chordoma. Radiographics. 23(4):995-1009, 20032.Nakasu Y et al: Tentorial enhancement on MR images is a sign of cavernous sinus involvement in patients with sellar tumors. AJNR Am J Neuroradiol. 22(8):1528-33, 20013.van den Berg R: Imaging and management of head and neck paragangliomas. Eur Radiol. 15(7):1310-8, 20054.Razek AA et al: Imaging lesions of the cavernous sinus. AJNR Am J Neuroradiol. 2009 Mar;30(3):444-52. Epub 2008 Dec 18. Review. Erratum in: AJNR Am J Neuroradiol. 30(7):E115, 2009D5.Schmidinger A et al: Natural history of chondroid skull base lesions--case report and review. Neuroradiology. 44(3):268-71, 2002D6.Lo WW et al: Endolymphatic sac tumors: radiologic appearance. Radiology. 189(1):199-204, 19937.Chong VF et al: Nasopharyngeal carcinoma. Eur J Radiol. 66(3):437-47, 2008D8.Yu T et al: Esthesioneuroblastoma methods of intracranial extension: CT and MR imaging findings. Neuroradiology. 51(12):841-50, 2009D9.Harnsberger R, Hudgins R, Wiggins P, et al. Diagnostic Imaging: Head and Neck. Salt Lake City, Utah: Amirsys, Inc. 2004.

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