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Skull Base Anatomy, Variants, Central Skull Base and Associated Foramina and “Don’T Touch Me” Lesions and Soft Tissues on CT and MR Nancy J

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Skull Base Anatomy, Variants, Central Skull Base and Associated Foramina and “Don’T Touch Me” Lesions and Soft Tissues on CT and MR Nancy J ASHNR 2017 Session 8: Temporal Bone & Skull Base – Part 2 Monday 9/18/17, 7:45-8:10 a.m. Learning Objectives • To review the anatomy of the anterior and Skull Base Anatomy, Variants, central skull base and associated foramina and “Don’t Touch Me” Lesions and soft tissues on CT and MR Nancy J. Fischbein, MD • To demonstrate selected anatomic variants Neuroradiology Section of these regions Stanford University Medical Center • To illustrate some of the common and less common “don’t touch” lesions of the region Disclosures • None Squama Newborn Anterior Skull Base • Frontal bone Orbital plate ANATOMY – Squama (vertical portion) – Orbital plate (horizontal portion) • Floor of anterior cranial fossa • Also ethmoid roof – Frontal sinus Adult • Ethmoid bone Squama – Cribriform plate Gray’s Anatomy – Ethmoid sinuses • Articulation Orbital plate – Posteriorly w sphenoid bone, superiorly w parietal bone Crista galli Ethmoid roof Olfactory groove Ethmoid Bone Crista galli • Four parts Cribriform Gyrus rectus – Horizontal or Perpendicular plate Olfactory plate apparatus cribriform plate Olfactory recess • Perforated by foramina for olfactory nerves – Perpendicular plate Cribriform level • Part of nasal septum Kallmann Syndrome – Paired lateral masses • Air cell labyrinths Olfactory Ant eth recess canal Ethmoid roof (fovea Olfactory recess ethmoidalis) is formed Post eth canal by orbital process of frontal bone Developmental defects/lesions may affect the anterior skull base. At Anterior Skull Base: Changes over Time all ages, be alert for meningocephaloceles. • At birth, ASB largely cartilaginous Frontonasal cephalocele • Ossification begins in roof of ethmoid labyrinth laterally and spreads to midline – Crista galli, perpendicular plate of ethmoid begin ~2 months, steady increase to ~14 months (Belden et al, AJNR 1997) Frontoethmoidal cephalocele B frontoorbital cephaloceles Birth: no ossification 3 mo: some ossification; 7 mo: thin but complete faint outline of CG bony bridge 31 F found down in apartment, dx’d w bacterial meningitis. Other developmental lesions may occur 1 day old male w difficulty breathing; also mild hypertelorism Central Skull Base • Sphenoid bone – Body; greater wings; lesser wings; pterygoid processes – Multiple skull base foramina and fissures for vessels and nerves • Occipital bone Central skull base, inner and outer surfaces (Frank Netter, Atlas of Human Anatomy) Dx: nasal glioma [no direct intracranial connection identified at surgery; there is also – Basiocciput contributes to clivus dysplasia of L anteroinferior frontal lobe and L olfactory apparatus] Occipital bone, outer surface (Grays anatomy) These are “don’t touch” in the sense of “don’t touch w/o considering that you may end up in brain and CSF” Sphenoid bone, posterior surface (Grays anatomy) Palatine foramina Pterygoid process Pterygopalatine fossa Orbit IOF Superior orbital fissure Foramen rotundum Optic canal NP * Hypoglossal canal Jugular foramen Clivus SS C OC Ca MCF CVJ J J CT Anatomy of Central Skull Base and Foramina SPF SOF FR OC AC PPF FO FO ST VC Carotid canal SS FS FS GWS PPF C C IOF P NP VC FO MR Anatomy of Central Skull Base and Foramina PPF Optic SOF FR nerve SS CS C PA VC FO Jugular foramen V3 below skull base NP Occipital condyles Clivus Chiasm Optic canals Hypoglossal canal Petrous apices Sella Ant clinoid Trigeminal nerves Foramen ovale SOF V3 F. Rotundum Vidian canal Central Skull Base: Changes Over Time, CT Central Skull Base: Changes Over Time, MR • Pneumatization of sphenoid sinus 18 mo F 6 F 10 F • Fusion of the spheno-occipital synchondrosis • Clival marrow: red to yellow 14 mo 3 yrs 8 yrs 52 yrs 18 mo: 10 yrs: Minimal sphenoid sinus pneumatization Larger sinus Prominent sphenooccipital synchondrosis Synchondrosis obliterating 16 F 67 F Adulthood: Large fully pneumatized sphenoid sinus Complete obliteration of sphenooccipital synchondrosis Some clival heterogeneity can be normal Initial MR Correlative CT 7 yrs later ANATOMICAL VARIANTS/ “DON’T TOUCH” LESIONS • Developmental variants or anatomical aberrations in bone, vessels, soft tissues • We don’t want to biopsy them or treat Same patient, age 57 them with stereotactic radiosurgery 50 yr old male • There are enough to fill entire textbooks! A few are selected Notochord Ecchordosis Physaliphora 31 M w HA. Incidental lesion noted that • Flexible rod-shaped • Ectopic notochordal remained stable in follow-up. body in embryos of Sphenooccipital remnant synchondrosis all chordates – Soft tissue mass – Composed of associated w mesoderm-derived Medial scalloping of basal posterior clivus cells canal – Defines primitive axis – T2 bright, non- of the embryo enhancing – Located ventral to • Typically incidental: neural tube asymptomatic, • In most vertebrates, indolent persists only as – Follow-up imaging if nucleus pulposus of unsure of dx intervertebral disc Nguyen R et al. AJNR Am J Neuroradiol 2009;30:803-807 Persistent Canals and Divots Absent Canals 39 M with R pulsatile tinnitus and vascular retrotympanic mass. Persistent Craniopharyngeal Canal Fossa Navicularis Magna Normal FS Absent FS Normal Enlarged IT canaliculus Aberrant ICA in ME carotid canal Type 3A, w cephalocele Other side Absent foramen spinosum w aberrant ICA, persistent stapedial a Congenital Absence of ICA/Carotid Canal Type 3B, w tumor (teratoma) CPC: Glastonbury et al, AJNR 2014 Petrous Apex Variations: Many Brain may herniate into Patient referred for bx Asymmetrical marrow Petrous Apex Cephalocele arachnoid pits 27 M w epilepsy. L temporal origin of seizures. May coexist with empty sella, arachnoid pitting, osseous- Dx: focal brain herniation into dural dysplasia -- Do consider possible association with arachnoid granulation/pit. Dx: prominent arachnoid granulation vs IIH (idiopathic intracranial hypertension) Patient did not have IIH. cephalocele of greater wing of sphenoid Another variant to recognize 43 F referred to our sinus center for biopsy of a skull base lesion. DON’T BIOPSY • Benign developmental variant • These may be actual lesions, but they can • Nonexpansile lesion w often be identified specifically enough that osteosclerotic they do not require biopsy, or biopsy can be Focal lesion of R basisphenoid. borders, internal HU: -28 fat, curvilinear dangerous, though they may require some Benign or aggressive? calcifications in basisphenoid or form of treatment adjacent skull base • And in some cases biopsy may be indicated, • Fatty marrow but one can still redirect from a plan to conversion, but then failure of resect to a plan to biopsy Dx: arrested pneumatization of the skull base pneumatization Welker et al, AJR June 2008 CT and MR are often complementary at 56 F w HA, R CN VI palsy the skull base. We are not just trying to get the clinicians to order more studies! Soft tissue lesion involving sella, central skull base. Met? Macroadenoma? Should we plan for biopsy? Let’s do an MR first a CTA/CECT would also be reasonable 21 F w new onset R CN XII palsy and HA during pregnancy. Dx: partially thrombosed giant aneurysm of R cavernous ICA. Patient was subsequently rx’d w flow diverting stents. 51 M referred for evaluation of clival chordoma after an MR ASL perfusion was performed for h/o HA Dx: presumed “cavernous hemangioma” [low flow venous vascular malformation] of bone. These can enlarge during pregnancy. Post- partum, symptoms resolved, and the patient is being followed. Dx: “benign fibro-osseous lesion generally c/w FD, but islands of woven bone are rare” How about this case? 39 M w HA, diplopia. 48 year old M w 3 year h/o R sided rhinorrhea. Dx: metastatic spindle cell sarcoma Dx: spontaneous lateral sphenoid cephalocele c/b CSF leak. Summary • Anterior and central skull base anatomy • Anatomical variants • Don’t touch lesions .
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