2 Skull Base Anatomy Review Skull Base BoundariesUpper surface of ethmoid bones and orbital plate of frontal bone to the occiptal boneThree Key BonesSphenoidTemporalOccipitalComplex areaKeep it simple
3 Skull Base Anatomy Review Temporal BoneTemporal bone- petrous portionSphenoid BoneOccipital BoneKey FissuresPetrosphenoidal fissurePetrooccipital fissureKey SuturesSphenosquamous SutureOccipitomastoid SutureGuidance for geographyDon’t mistake for fx
4 Skull Base Anatomy Review Key OpeningsForamen spinosumForamen ovaleForamen lacerumForamen rotundumForamen magnumForamen of vesaliusJugular foramenSuperior orbital fissureInferior orbital fissureOptic canalVidian canalHypoglossal canalPterygopalatine fossa7 foramina2 fissures3 canalsAll with fun stuff inside.
7 Skull Base Anatomy Review Foramen magnumMedulla oblongataVertebral arteriesAnterior/Posterior spinal arteriesHypoglossal canalCN XIIHypoglossal arteryHypoglossal artery = not always present.Sometimes, can have a small emissary vein that runs through here that can protrude into the cerebellomedullary cistern and mimic a nerve sheath tumor.**
8 Skull Base Anatomy Review Jugular ForamenPars nervosa: CN IX, inferior petrosal sinusPars vascularis: CN X, XI, jugular bulb*2 parts:Pars nervosa = anteromedialPars vascularis aka pars venosa = posterolateralSeparated by the jugular spur.Pars nervosa: glossopharyngeal nerve,inferior petrosal sinus- runs along petrooccipital fissurePars vascularis: vagus and spinal accessory nerveJugular bulb: confluence b/w sigmoid sinus and internal jugular vein.Anterolateral to pars nervosa = petrous portion of the carotid artery.* Carotid canal
9 Skull Base Anatomy Review Foramen SpinosumMiddle meningeal artery/veinCV V3, recurrent branchLesser superficial petrosal nerveForamen OvaleCN V3Lesser petrosal nerveAccessory meningeal arteryEmissary veinsForamen of VesaliusEmissary veinAccessory meningeal artery- asc intracranial branchF.S.:V3 recurrent = mandibular branch.Emissary veins in FS and FO connect cavernous sinus with pterygoid plexus of veins = path for nasaopharyngeal tumors.Foramen of vesalius- inconstant. Anterior and medial to f. ovale. When it does occur, it contains (read slide)
10 Skull Base Anatomy Review Foramen LacerumAscending pharyngeal artery- meningeal branchNerve of pterygoid canalVidian Canalaka pterygoid canalPterygopalatine fossa - foramen lacerumVidian nerveVidian arteryF.L.:read slideVidian canal = aka pterygoid canal. Connects pterygopalatine fossa to foramen lacerum. Contains vidian artery (branch of maxillary artery) and nerve.Vidian nerve = formed by merger of greater superficial petrosal nerve (branch of facial nerve) and deep petrosal nerve.
11 Skull Base Anatomy Review Foramen rotundumCN V2Artery of foramen rotundumEmissary veins
12 Skull Base Anatomy Review Pterygopalatine FossaPterygopalatine ganglia V2Pterygopalatine plexusCommunicates with:Inferior orbital fissureOrbital apexSphenopalatine foramenPterygomaxilary fissureForamen rotundumVidian canalGreater/lesser palatine canals and foraminaPPF = conduit for spread of tumor and infectionCommunicates with inf orbital fissure, orbital apex,…PPF - Sphenoplatine foramen = to nasal fossaPPF – pterygomaxillary fissure = to masticator spacePPF- foramen rotundum = connection with Meckel’s cave, cavernous sinusPPF- Vidian canal = to foramen lacerumPPF- to greater/lesser palatine canals = to palate
13 Skull Base Anatomy Review Cavernous SinusReceives: Superior opthalmic vein Inferior opthalmic vein Sphenoparietal sinusDrains via: Petrosal sinuses Basilar plexus Pterygoid plexusConnection: Circular sinusContains: CN III, IV, V1, V2, VIPPF – foramen rotundum = connection with meckel’s cave, cav sinus, since we’ve mentioned it a few times now and b/c contains a lot of key elements:Cav sinus- read slide.V2- lateral wall of CS- then to foramen rotundumV1- lateral wall of cav sinus- then to superior orbital fissure, along with CN III, IV, VIMeckel’s CavePosterior aspect of cavernous sinusGasserian ganglion (sensory root ganglion of CN V)
14 Skull Base Anatomy Review Superior Orbital FissureCN III, IV, V1, VIMiddle meningeal artery- orbital branchRecurrent meningeal arterySuperior opthalmic veinInferior Orbital FissureInfraorbital artery, vein, and nerve (V2 branch)Optic CanalOptic nerveOpthalmic arterySpeaking of the superior orbital fissure…Below SOF = IOF.Optic canal = more superior to SOF.
15 Skull Base Anatomy Review Key OpeningsForamen spinosumForamen ovaleForamen lacerumForamen rotundumForamen magnumForamen of vesaliusJugular foramenSuperior orbital fissureInferior orbital fissureOptic canalVidian canalHypoglossal canalPterygopalatine fossa
16 Skull Base Pathology Meningioma Chordoma Metastases Chondrosarcoma MyelomaNeuromaSchwannomaVascular AneurysmChordomaChondrosarcomaDermoid tumorsEpidermoid tumorsGlomus tumorsChordomas like the clivusChondrosarcomas like the cartilaginous endplates- petrooccipital sutureGlomus tumors- jugular bulb, middle ear, carotid bodyMeningiomas- most common (20% of all brain tumors). But most = cerebral convexity, along and lateral to the falx.10% clivus20% sphenoid ridgeSchwannomas almost always develop from sensory nerves. Because the olfactory and optic nerves do not have a Schwann cell layer, they do not develop these tumors. The most common intracranial schwannoma = acoustic neuroma- it develops from the vestibular nerve. Bilateral acoustic neuromas = pathogomonic for NF2. (90% of the time, schwannomas are solitary).The second most common intracranial schwannomas develop from the trigeminal nerve. Trigeminal schwannomas usually arise from the root or ganglion and occupy the middle fossa and, sometimes, the posterior fossa. Schwannomas of the other cranial nerves are rare.
17 Case 1T1 post contrast MR showing extraaxial lesion arising from the middle cranial fossa.Heterogeneous enhancement.Low signal areas = flow voids or calcs.Coronal = involvement with skull base. Mass effect on temporal lobe.
18 Chondrosarcoma CT Findings: MRI Findings: Irregular, destructive mass Centered off midlinePetro-occipital fissureCalcifications, 70%; “rings/arcs”MRI Findings:Low T1 signal, high T2 signalEnhance with contrastScalloped, well circumsribed margins
19 Chondrosarcoma Origin: Location: Clinical: Preexisting cartilaginous lesion, synchondroses, cartilage endplatesLocation:Paranasal sinuses, skull base, parasellar regionLong bones, pelvis, sternum, ribsClinical:45 yo, median ageClassic, mesenchymal, or dedifferentiatedChondrosarcomas can occur anywhere in the skeletal system. Often = preexisting cartilaginous lesion like previously benign osteochondroma. In skull base = usually at cartilage endplates. E.g. petrooccipital suture.Location: read slideClinical:Most commonly, patients are diagnosed with chondrosarcomas during the third or fourth decade of life. Males are affected more often than females. Chondrosarcomas can be divided into classic, mesenchymal, and dedifferentiated tumors.Mesenchymal, Dedifferentiated = high grade.Classic low grade = like chordoma.DDX: Chordoma- usually has marked bone destruction, midline (clivus)Chondrosarcoma = significant soft tissue component, little bone destruction, arcs/nodules of calcification, eccentric locations- often centered in framen lacerum.
20 Case 2Sagittal T1-weighted MR image shows a large, hypointense soft-tissue mass that arises from the distal clivus with anterior extension into the nasopharynx (arrows) and extradural extension into the posterior fossa (arrowhead).
21 Chordoma CT/MRI Findings: DDx: Expansile lytic lesion, midline Well delineated mass arising from boneLarge soft tissue componentVariable calcificationAnteroposterior extensionHeterogeneous enhancement on T1, T2Dark on T1, bright on T2CT to assess degree of bone involvement. MRI to evaluate extension of tumor.CT Findings:The most characteristic appearance of intracranial chordoma is of a centrally located homogeneous soft tissue mass arising from the clivus and causing adjacent bone destruction.Calcification is common but variable.Areas of low attenuation within the soft tissue mass occasionally are found on CT, representing the myxoid and gelatinous material found on pathologic examination.CT reliably demonstrates petrous apex involvement and lysis of the skull base foramina.MRI Findings:Mass originating from midline with extension primarily in the anteroposterior axis rather than laterally.Well delineated.Expands bone in the early stage = indicator that it arises from bone, not from adjacent structures.Post gad = lobulated area, heterogeneous on T1 and T2 b/c of mucinous and gelatinous contents.DDX: Chondroma- similar appearance but extend more laterally into sellar and cerebellopontine angles.Clivus meningioma – homegeneous signal, dural attachmentDDx:ChondromaChondrosarcomaClivus meningioma
22 Chordoma Origin Location Clinical Notochord remnants Clivus 35% Sacrum 50%, Vertebral bodies 15%Clinicalage 30-70Slow growing, locally aggressiveCN VI- CN deficitsMets lateTx: surgery, radiationContrast enhanced T1 spin echo image. Chordoma of the upper part of the clivus with posterior extension into the pontine cistern.Chordomas = benign tumor but has significant problems b/c of location, local invasion, recurrence.Origin:Notochord = early fetal axial skeleton. Gets surrounded by cartilage. Cartilage ossifies and notochord = squeezed out into intervertebral regions = nucleus pulposus of intervertebral disks.Can get remnants then, along any position of the neural axis- turn into chordomas.Location: read slide. Rare. <0.2% of all intracranial tumors.Clinical:read slideCN deficits: HA, dysphagia, facial pain, facial paresis, visual loss, hearing loss, and ataxia.CT to assess degree of bone involvement. MRI to evaluate extension of tumor.CT Findings:The most characteristic appearance of intracranial chordoma is of a centrally located homogeneous soft tissue mass arising from the clivus and causing adjacent bone destruction.Calcification is common but variable.Areas of low attenuation within the soft tissue mass occasionally are found on CT, representing the myxoid and gelatinous material found on pathologic examination.CT reliably demonstrates petrous apex involvement and lysis of the skull base foramina.MRI Findings:Mass originating from midline with extension primarily in the anteroposterior axis rather than laterally.Well delineated.Expands bone in the early stage = indicator that it arises from bone, not from adjacent structures.Post gad = lobulated area, heterogeneous on T1 and T2 b/c of mucinous and gelatinous contents.
23 Case 3CT imaging demonstrates the extent of bony destruction (white and black arrows) by the tumor. The normal jugular foramen on the left (arrow head) is shown for comparison.
24 Glomus jugulare CT/MRI Findings: Glomus TumorGlomus jugulare CT/MRI Findings:Center: jugular foramenLimit: hyoid boneEnhance w/ contrastSalt and pepper appearance on MRIBone erosionSalt and pepper: multiple low signal intensity areas = flow voids in tumor.When large- erode bone.
25 Glomus Tumor Origin: Location: Clinical: Chemoreceptor cells 10% multipleglomus jugulare: jugular bulbglomus tympanicum: cochlear promontory;Clinical:Pulsatile tinnitusHearing lossarrythmia, BP fluctuationGlomus tumors arise from chemoreceptor cells.These tumors are slow-growing hypervascular tumors that usually occur in the temporal bone.Location: read slide- check other places for them b/c = multiple. E.g. Carotid bodyPatients usually present with gradual hearing loss, unilateral pulsatile tinnitus, and lower cranial nerve palsies.Approximately 1-3% of gangliogliomas produce catecholamines, so can get arrythmia, BP fluctuation.May be locally invasive but rarely metastasize.
26 ReferencesErdem E, et al, “Comprehensive Review of Intracranial Chordoma”, Radiographics 2003; 23:Grossman, R et al, Neuroradiology: The Requisites, Mosby, Philadelphia, 2003Peretti P et al, “Chordoma”,Pluta R et al, “Glomus Tumors”,Small J et al, “Chondrosarcoma”,Weissleder, R et al, Primer of Diagnostic Imaging, Mosby, Philadelphia, 2003