Phillips Developmental Skull Base Lesions 2018 (1).Pptx

Disclosures

• I have no pertinent financial disclosures Skull Base Developmental Lesions

C Douglas Phillips MD FACR Director of Head and Neck Imaging and Professor of Radiology NewYork-Presbyterian Hospital/Weill Cornell Medical College

Significance of Skull Base Topics to Discuss Developmental Lesions • People basically hate the skull base • Embryology and development of normal – It is a region where people often turn off skull base – “If I don’t see you, you’re not there” • Skull base foramina, fissures, and surface • Developmental lesions are relatively features common • Normal variations of skull base • Developmental lesions are often “leave- me-alone-lesions” • Maldevelopmental lesions of anterior, • HOWEVER, they may resemble pathology central, and posterior skull base – Doctors want to do things to them

Skull Base Regions

• Anterior • Ossification via – CN I enchondral bone • Central formation – CN II, III, IV, V, VI • Develops from individual sheets • Temporal bone woven together – CN VII, VIII, ICA with cartilage • Posterior • Potential for many – IJV, CN IX, X, XI, XII; foramina Anterior Skull Base Anterior Skull Base Maldevelopmental Lesions • Bony elements • Sinonasal encephaloceles – Frontal, ethmoid, and • Nasal glial heterotopias sphenoid bone • CN I is dominant CNS • Nasal dermoid and dermal sinus feature • NF 1 bony dysplasia • Interface of CNS and sinonasal cavity

Normal Nasal Development Normal Nasal Development 4-6 weeks After 8 weeks

• Frontal bone and nasal • Dural diverticulum bone develop externally regresses • Nasal capsule (S) – Remnant is foramen cecum develops under them • Prenasal space obliterated – Cartilaginous interior of frontonasal process – Nasal bones fuse with nasal – Becomes ethmoids capsule • Fonticulus frontalis (f) • Fonticulus frontalis • Dural diverticulum (d) obliterated projects anteriorly into – Remnant is nasofrontal prenasal space suture

Illustration modified from Imaging the Illustration modified from Imaging the Pediatric Head, Neck and Spine Pediatric Head, Neck and Spine Castillo and Mukherji Castillo and Mukherji Anterior Skull Base Encephaloceles

• Contain herniated frontal lobes • Frontonasal are majority of lesions – Present as mass over nasal dorsum • Nasoethmoidal are less common – Present in nasal cavity • Nasolateral are rare – Herniate into orbits • Naming convention for encephaloceles – Roof is first named item – Floor is second named item

Frontonasal Encephalocele Frontonasal Encephalocele

Illustration modified from Imaging the Pediatric Head, Neck and Spine Courtesy of Anton Hasso, MD Castillo and Mukherji Courtesy of Anton Hasso, MD

Frontonasal Encephalocele Nasoethmoidal Encephalocele

• Brain herniates into persistent dural diverticulum • Encephalocele presents as nasal mass • Mass in superior nasal cavity – LOOK AT SKULL BASE

Illustration modified from Imaging the Pediatric Head, Neck and Spine Castillo and Mukherji Nasoethmoidal Encephalocele Nasoethmoidal Encephalocele

Illustration modified from Imaging the Pediatric Head, Neck and Spine Castillo and Mukherji

Nasal Glial Heterotopia Extranasal Glial Heterotopia “Nasal Glioma” • Development analogous to encephalocele • Defect closes leaving CNS tissue outside: • Frontonasal encephalocele – Extranasal glial heterotopia • Nasoethmoidal encephalocele – Intranasal glial heterotopia

Extranasal Glial Heterotopia Intranasal Glial Heterotopia

Diagnosis may be unsuspected and may be misdiagnosed by pathology. Immunoreactive for GFAP and S100.

Courtesy of Rick Wiggins, MD Nasal Dermoid/Dermal Sinus Nasal Dermoid

• Dural diverticulum persists longer than normal in contact with nasal dermal structures • Can drag nasal dermal structures back with it as it later regresses • Ectoderm lines dermal sinus – Occasional dermoid or epidermoid masses along tract

Illustration modified from Imaging the Pediatric Head, Neck and Spine Intracranial dermoid at foramen cecum Castillo and Mukherji

Nasal Dermal Sinus Nasal Dermal Sinus

• Patients may have characteristic nasal pit • Can occasionally express fluid

Nasal Dermal Sinus Bony Dysplasias

• Hypodevelopment or maldevelopment of sphenoid • Accompany NF • Rare isolated dysplasia

Courtesy of Stephen Park MD “Empty Orbit” of Sphenoid Buphthalmos and Sphenoid Dysplasia Dysplasia

Sphenoid Dysplasia Lateral Sphenoid Defect

Courtesy of Greg Petermann, MD

Central Skull Base Anatomy Central Skull Base Anatomy The “Holey Land” • Central skull base • Foramen and fissures – Posterior to lesser – Optic canal wing of sphenoid / – Superior orbital fissure (SOF) planum sphenoidale – Inferior orbital fissure – Anterior to petrous (IOF) ridge/dorsum sella – Carotid canal – Foramen rotundum – Foramen ovale – Foramen spinosum – Foramen lacerum – Vidian canal Central Skull Base Variant Foramina of Skull Base Maldevelopmental Lesions • Variant foramina • More than you can count • Encephaloceles • Often no more than anatomic curiosity – Canal of Sternberg when perusing normal skull base • Described variants include: • Vascular hypoplasia/aplasia – Foramen of Vesalius • NF 1 bony dysplasia – Palatovaginal canal • Sphenoid benign osseous lesion – Canaliculus innominatus – AKA “Non-pneumatized sphenoid” • More important variants may be confusing, appear as pathology

Persistent Craniopharyngeal Canal Persistent Craniopharyngeal Canal (PCC) • Midline vertical conduit in basisphenoid which may contain dura and vascular structures – Can be quite large and may extend to sella – Can contain pituitary tissue • Larger varieties may be termed transsphenoidal canal • May be associated with craniofacial anomalies and nasopharyngeal mass

Fossa Navicularis Magna Canalis Basilaris Medianus

• Notch in basiocciput • Remnant of cephalic containing pharyngeal end of primitive tonsillar tissue notochord • Likely related to • Intracranial surface of notochordal remnant basiocciput in the that inhibits midline development of • May be complete or normal basiocciput incomplete

Romiti G. La fossetta faringea nell’osso occipitale dell’uomo. Atti Soc Toscana Sci Nat 1890;11 Jacquemin C et al. Canalis basilaris medianus: MRI. Neuroradiology 2000;42:121-123. CBM – Complete Variant CBM – Incomplete Variant

Courtesy of Deborah Shatzkes MD

Basal Encephaloceles Lateral Sphenoid Encephaloceles

• Transsphenoidal • Relatively rare – Sphenoid bone into sinus or nasopharynx • Sphenoorbital • More likely to be occult, and present later – SOF into orbit – CSF leaks, meningitis • Sphenoethmoid – Junction of sphenoid/ethmoid into posterior nasal • Clinical and radiological diagnosis may be cavity difficult • Transethmoid – Unsuspected – Through ethmoid into anterior nasal cavity • Sphenomaxillary • “Cyst” in sphenoid sinus is an – IOF into pterygopalatine fossa encephalocele until proven otherwise

Sphenoid Encephalocele

Bone defect is lateral sphenoid wall in setting of significant pterygoid pneumatization inferior and lateral to foramen rotundum and superior to vidian canal Sternberg’s Canal Transalar Sphenoid Encephalocele

• Lateral wall of sphenoid • Associated with lateral “spontaneous” CSF leaks/encephaloceles • Reported in up to 4% of adults • Doesn’t correspond to typical lateral encephalocele – Sternberg’s Canal must be medial to V2

From Elster AD, Branch CL Jr. Transalar sphenoidal encephaloceles: clinical and Barañano CF et al. Sternberg's canal: fact or fiction? Am J radiologic findings. Radiology. 1989 Jan;170(1 Pt 1):245-7 Rhinol Allergy. 2009 Mar-Apr;23(2):167-71

Vascular Dehiscence Transalar Sphenoid Encephalocele Carotid Dehiscence

Location corresponds to enlarged foramen ovale

Posterior Skull Base Posterior Skull Base Anatomy Maldevelopmental Lesions • Posterior to dorsum • Brief word of carotid anomalies sellae • Clivus anomalies and variant foramen • Basiocciput and clivus • Ecchordosis physaliphora • Foramen magnum, jugular foramen, and • Sphenoid and occipital hypoplasia internal auditory • NF 1 bony dysplasia canals • Arnold-Chiari and Dandy-Walker • CNs VII-XII malformations Benign Developmental Fatty Pseudolesion of Sphenoid • Referred to as “arrested pneumatization” – Benign intraosseous lipoma • “Bubbly” lesion of sphenoid • Differential diagnosis of chondroid lesions • Characteristic presence of fat in lesion – Similar to “hemangioma” of vertebra • Associated hypodevelopment of sphenoid sinus

Courtesy of Rick Wiggins, MD

“Arrested Pneumatization”

Seen in children/increased incidence in patients with chronic anemias (SSD, thalassemia)

Notochord Remnants Ecchordosis Physaliphora Chordoma, EP & Thornwaldt Cyst

Benign variant of chordoma
T2 hyperintense
Key differentiation
Absence of enhancement
Smooth bony margins
Has common intradural component
Described in 2-3% of population in autopsy series Gray Gelatinous Notochord Tissue

T1 Hypointense T2 Hyperintense NO Enhancement

Chordoma Chordoma

Midline Bone Bulky, lobulated, destructive mass Destruction Aberrant ICA Congenital Absence of ICA

Occipital Bone - Normal Development of Clivus

Courtesy of Wendy Smoker, MD

Occipital Condylar Hypoplasia with Occiput-C1 Assimilation Basiocciput Hypoplasia

Courtesy of Wendy Smoker, MD Occiput-C1 Assimilation Arnold Chiari I Malformation

Courtesy of Wendy Smoker, MD

Arnold Chiari II Malformation Arnold Chiari III Malformation

• Tonsillar herniation • Fenestration/ hypoplastic falx with interdigitated gyri • Tectal “beaking” • Concave clivus and temporal bones • “Lacunar” skull • Neural tube defect

Courtesy of Wendy Smoker, MD

Dandy-Walker Malformation with Conclusions Myelocystocele • Many normal and variant skull base foramina and knowledge of normal variants can keep you out of trouble • Anterior skull base anomalies can present in nasal cavity • Developmental lesions are common findings in the central skull base

Courtesy of Wendy Smoker, MD