Skull base


unossified gaps in the anterior cribriform plate. Coronal Progression of Anterior Skull Base Ossification. 1 week old Coronal CT through the anterior ...

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Get Wise About Cracks: A Pictorial Review of the Pediatric Skull Base eEdE-203 Anna Thomas MD, John Egelhoff DO, John Curran MD, Jeffrey Miller MD, Richard Towbin MD.

DISCLOSURES: • None

Objectives 1. Review the normal anatomic landmarks of the skull base and its 3 main divisions. 2. Review normal development and progression of ossification of the different divisions of the skull base. 3. Review normal skull base lucencies and foramina of the pediatric skull base. 4. Present a few cases of pediatric skull base fractures and discuss their associated complications. 5. Review frequently associated complications associated with specific skull base fracture locations.

Overview Skull base: • Comprised of 7 bones: * paired frontal * paired temporal * unpaired ethmoid * unpaired sphenoid * unpaired occipital

• 3 divisions: anterior, central, and posterior form the floor of the anterior, middle, and posterior cranial fossae. From: Baugnon, KL et al. Neuroimag Clin N Am 24 (2014) 439–465.

Review of the Atraumatic Skull Base

Anterior Skull Base - Axial

Mildly Adapted From the Textbook: Diagnostic and Surgical Imaging Anatomy of the Brain. Head & Neck. Spine.

Anterior Skull Base -Sagittal

From Textbook: Diagnostic and Surgical Imaging Anatomy of the Brain. Head & Neck. Spine.

Age Related Anterior Skull Base Ossification Birth: Nonossified. 2 years: only 4% have a fully ossified anterior skull base. 4/+ years: fully ossified anterior skull base. > 4 years: the foramen cecum is the only nonossified portion.

Adapted from: Koch BL. Neuroimag Clin N Am 2014;24:513–529.

Coronal Progression of Anterior Skull Base Ossification 1 week old Coronal CT through the anterior skull base: Most of the anterior skull base including crista galli, cribriform plate and perpendicular plate of ethmoid bone are unossified. There is a large gap between the orbital plates of frontal bones. Ethmoid air cells are not yet developed. 2 year old coronal CT through anterior skull base: Ethmoid bone is now mostly ossified, particularly crista galli & cribriform plate. Note the normal unossified gaps in the anterior cribriform plate.

18 Year old coronal CT through anterior skull base which is completely ossified. Ethmoid air cells extend superolateral to plane of the cribriform plate. The fovea ethmoidalis is connected to the cribriform plate by the lateral lamella.

Axial Progression of Anterior Skull Base Ossification

Normal Lucencies & Foramina of the anterior skull base

Foramina of the Anterior Skull Base Optic Nerve Canal

Superior Orbital Fissure

Contents Cranial Nerve II, Ophthalmic artery, and sympathetic nerve fibers. Cranial Nerves III, IV, V1, VI and the Superior Ophthalmic vein

Central Skull Base

Mildly Adapted From the Textbook: Diagnostic and Surgical Imaging Anatomy of the Brain. Head & Neck. Spine.

Central Skull Base Foramina & Contents Foramina of the central skull Base

Contents

Foramen rotundum

Cranial Nerve V2

Foramen ovale

Cranial Nerve V3

Carotid canal

Internal Carotid artery and Sympathetic plexus

Foramen spinosum

Middle Meningeal artery

Vidian canal

Vidian nerve and artery

Foramen lacerum

Cartilage

Diagram of Central & Posterior Skull Base Ossification Centers

*Indicates olivary eminence From: Nemzek WR et al. AJNR Am J Neuroradiol 2000;21:1699-1706.

Normal Neonatal Central Skull Base Lucencies & Ossification Centers on the Axial Projection Axial CT image of the central skull base in a 1 week old: Olivary eminence ( ), also called the anterior foramen is a triangular shaped lucency seen only in the early newborn period; This is located posterior to the presphenoid ( ) and anterior to the paired postsphenoid ossification centers ( ). Note the posterior and centrally located posterior foramen ( )also called the craniopharyngeal canal.

Progression of Skull Base Ossification

Black arrow ( )shows normal sequence of skull base ossification in a posterior to anterior direction.

From: Nemzek et al. AJNR Am J Neuroradiol 2000;21:1699-1706.

Maturation of the Central Skull Base - Sagittal Midline central skull base in a 1 week old: A patent spheno-occipital synchondrosis ( ) and a partially patent craniopharyngeal canal ( ) are noted. Midline central skull base in a 2 year old: Spheno-occipital synchondrosis ( ) is patent and its comprising bones are more uniform in density . A thin sclerotic line persists at expected site of the craniopharyngeal canal ( ). Note the ossifying cribriform plate and small ethmoid and sphenoid sinuses Midline central skull base in an 18 year old: The spheno-occipital synchondrosis ( ) is completely fused. Note the completely ossified cribriform plate and mature ethmoid and sphenoid sinuses.

Synchondroses & Sutures of the Central Skull Base Name Spheno-occipital synchondrosis

Craniopharyngeal canal (Posterior Foramen) Olivary eminence

Canalis basilaris medianus

Location

Pertinent Information

Located between and separates the postsphenoid ossification center from the basiocciput

Where maximal skull base growth occurs. Remains patent until teenage years. Small ossified bodies can be seen at the synchondrosis during closure. After complete closure, small divots, clefts, or fissures on one or both sides of this synchondrosis are often seen.

Extends from the floor of the sella turcica to the roof of the nasopharynx

Seen a partially patent canal in a only small percentage of infants, with usual closure in early infancy. Rarely, is pathologically widened from a cephalocele containing the ectopic pituitary.

Triangular shaped, cartilaginous lucency seen in early newborn period between presphenoid and the paired postsphenoid bodies

Seen only in early newborn period. Rarely visible as a sclerotic remnant in a small percentage of children over 9 months of age.

Midline lucency in the basiocciput posterior to the spheno-occipital synchondrosis

Very rarely seen as incidental finding that may be associated with nasopharyngeal cysts. Variable in shape and patency ( can be complete /incomplete).

Posterior Skull Base

Both images are from Textbook: Diagnostic and Surgical Imaging Anatomy of the Brain. Head & Neck. Spine.

Posterior Skull Base Foramina & Contents Foramina of the Posterior skull Base

Contents

Internal Auditory Canal

Cranial nerves VII & VIII and labyrinthine artery Cranial nerve VII & stylomastoid artery Cranial nerves IX, X, & XI, internal jugular vein, inferior petrosal vein & sigmoid sinus Cranial nerve XII

Stylomastoid Foramen Jugular Foramen

Hypoglossal Canal Foramen Magnum

Medulla oblongata, ascending spinal fibers of cranial nerve XI, vertebral arteries, and anterior & posterior spinal arteries

Posterior Skull Base Ossification Mastoid and Petrous Temporal bone segments

Cartilaginous & Membranous Components of the Skeletally Immature Occipital Bone

Note: (

) refers to mendosal suture.

Skull Base Trauma

2 year old s/p MVA with magnified coronal (above) and axial ( left) images through the right temporal bone: Blue arrow: right temporal bone fracture. Yellow arrow: resultant disruption of right middle ear ossicles and loss of normal ice cream cone configuration of the incudomalleal joint.

2 year old who was backed over by a car: White arrow: vertical fracture through sphenoid extending to the sella. This child manifested with clinical signs of Diabetes insipidus within days of this injury. Yellow arrows: preclival soft tissue swelling.

Magnified image of the sphenoid bone in the same patient: White arrow: vertical fracture through sphenoid extending to the sella. This child manifested with clinical signs of Diabetes insipidus within days of this injury. Yellow arrows: preclival soft tissue swelling.

7 year old ejected during MVA: Far right sagittal CT image demonstrates abnormal widening of the joint space between the right occipital condyle with right superior C1 facet (blue arrow) in this patient with atlantoccipital dislocation.

7 year old ejected from car during MVA: Blue arrow - marked thickening of preclival soft tissues. Yellow arrow - retroclival hematoma.

7 year old ejected during MVA: Coronal image demonstrates abnormal widening of the joint space between the occipital condyle and the superior C1 facet on both sides (blue arrows) in this patient with atlantoccipital dislocation.

8 year old with focal expansion of the skull . Yellow arrows: Note the focal abnormal expansion of the right sigmoid fossa and this abnormality was in the region of an old fracture. There is a post-traumatic dural tear with leptomeningeal herniation at the fracture site resulting in progressive skull erosion at the fracture site from continuous CSF pulsations.

8 year old s/p head injury with left posterior calvarial fracture and resultant post traumatic thrombosis of left transverse sinus: White arrows: obliquely oriented fracture through left occipital bone extending across left lambdoid suture into petrous segment of left temporal bone. Yellow arrow: intracranial air adjacent to left sigmoid sinus. Blue arrows: abnormal isointense T2 signal ( thrombus) replacing normal dark flow void of the left transverse sinus. Orange arrows: left transverse sinus is absent on the MRV.

Common Complications Associated with Specific Skull Base Fracture Locations Fracture Location:

Common Complications:

Anterior Skull Base

Intraorbital Injury Sinonasal CSF leak/meningoencephalocele

Central Skull Base

Internal carotid artery injury Injury to Cranial Nerves II, III, IV, V, or VI Horner Syndrome

Posterolateral Skull Base (Nonsquamous Temporal Bone)

Internal carotid artery injury Injury to Cranial Nerves VII or VIII Mastoid CSF leak/meningoencephalocele Injury to middle and inner ear structures

Central Posterior Skull Base

Major venous vessel injury Vertebrobasilar arterial injury Injury to Cranial Nerves IX, X, XI, or XII Injury to craniocervical junction/upper cervical spine

Adapted from: Baugnon, KL et al. Neuroimag Clin N Am 24 (2014) 439–465.

References: 1. Baugnon KL, Hudgins PA (2014) Skull Base Fractures and Their Complications. Neuroimag Clin N Am 24:439-465. 2. Koch BL. Pediatric Considerations in Craniofacial Trauma (2014) Neuroimag Clin N Am 24:513–529. 3. Nemzek WR, Brodie HA, Hecht ST , Chong BW, et al (2000) MR, CT, and Plain Film Imaging of the Developing Skull Base in Fetal Specimens AJNR Am J Neuroradiol 21:1699-1706. 4. Madeline LA, Elster AD (1995 ) Suture closure in the human chondrocranium: CT assessment. Radiology 196: 747-756. 5. Harnsberger HR, Osborn AG, Macdonald A, Ross J (2006) Diagnostic and Surgical Imaging Anatomy of the Brain. Head & Neck. Spine. Amirsys Incorporated.