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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_6009_Библиотеки_им_академика_М_И_Перельмана.pdf
Paracondylar Process
KEY FACTS
TERMINOLOGY
• Paramastoid process, paroccipital process, jugular process,
parajugular process
• Enlarged bony process of cranial base projecting caudally to
transverse process of atlas (C1)
• Uncommon variant (~ 0.5%)
IMAGING
• Many variants, ranging from small hump of bone
(paracondylar tuberculum) to free-ended process or jointed
with transverse process of C1
Congenital and Genetic Disorders
○ If not attached to occipital bone, process is isolated rod-
like bony element called massa paracondylica
○ Portions may be pneumatized from mastoid air cells
TOP DIFFERENTIAL DIAGNOSES
• Assimilation of C1 into occiput
○ Bony fusion across occipital condyles and lateral masses
of C1
(Left) Coronal NECT shows a
large bony mass projecting off
the right occipital condyle ſt
and merging with an enlarged
right transverse process of C1
with a neoarticulation st. The
vertebral artery has a welldefined canal through the
bony mass . (Right) Axial
NECT shows the junction of
the right paracondylar process
with the markedly enlarged
right transverse process of C1
ſt. The paracondylar process
shows considerable variation,
ranging from a small tubercle
to a large bony process.
• Klippel-Feil syndrome
○ Variable fusions of multiple cervical vertebral bodies and
posterior elements
• Proatlas segmentation abnormality
○ Shelf-like bony projection arising from ventral foramen
magnum or occipital condyle
CLINICAL ISSUES
• Typically asymptomatic
• May cause limitation of neck movement and restricted
range of motion
• Rare cases of chronic headache pain relieved by surgical
resection of paracondylar process
• Rare reports of associated vertebral stenosis
• May be associated with other abnormalities
○ Assimilation of anterior arch of C1 with anterior foramen
magnum
○ C2-C3 fusion
90
(Left) Coronal NECT shows a
large, well-defined, and
corticated bony fusion that
has occurred on a congenital
basis connecting the mastoid
region to the transverse
process of C1 ſt. This is
usually asymptomatic,
although there are rare
reports of associated vertebral
artery stenosis. (Right)
Sagittal NECT shows the
paracondylar process as a
large, cone-shaped, corticated
bony mass extending inferiorly
from the occipital condylar
region ſt.
Condylus Tertius
KEY FACTS
Congenital and Genetic Disorders
TERMINOLOGY
• Condylus tertius
○ Bony process in median line at front rim of foramen
magnum, articulated with tip of dens or anterior C1 arch
○ Uncommon variation = 0.5-5.0% incidence
○ Medial residue of hypochordal arch of proatlas (4th
occipital sclerotome)
○ Forms joint or pseudojoint with clivus, odontoid process,
or anterior arch of C1
• Basilar process (processus basilaris)
○ Bony variant in similar region as condylus tertius but with
slightly different imaging features and different
embryology
○ Also known as mammillary or papillary processes
○ Uncommon = 4% incidence
Unilateral or bilateral, paramedian, sphere-shaped bony
○
projections off of anterior inferior margin of foramen
magnum
○ Lateral residue of hypochordal arch of proatlas
TOP DIFFERENTIAL DIAGNOSES
• Proatlas segmentation abnormality
○ Larger horizontal bony excrescence with significant cord
or cervicomedullary junction compression
• Os odontoideum
○ Rounded, corticated, separate bony density with no
normal odontoid process
• Os avis
○ Failure of fusion of odontoid tip to remainder of C2
• Degenerative osteoarthritis of C1-C2
• Condylar fracture with displacement
CLINICAL ISSUES
• Typically incidental finding
• Rarely may be cause of limitation of range of motion of
craniovertebral junction due to joint or pseudojoint with C1
arch
(Left) Sagittal NECT shows a
condylus tertius as a wellcorticated bony projection
arising off of the inferior
midline aspect of the clivus
ſt, which articulates with the
superior aspect of the
odontoid process and the
superior aspect of the anterior
arch of C1 . (Right) Axial
NECT shows a midline, wellcorticated bony projection
from an anterior aspect of the
clivus ſt. The midline position
differentiates this condylus
tertius from the basilar
process, which has a position
that is off of the midline.
(Left) Coronal CTA
demonstrates the typical
appearance of basilar
processes ſt, which are seen
as paired spherical bony
projections to either side of
the midline of the clivus that
extend inferior to articulate
with the superior aspect of the
C1 arch. (Right) Sagittal CTA
shows the orientation of the
basilar process ſt, just off of
midline, with its articulation
with the superior aspect of the
C1 arch .
91
Posterior Arch Rachischisis
KEY FACTS
TERMINOLOGY
• Synonym: Incomplete C1 posterior ring
• Definition: Posterior C1 arch is incompletely formed with
midline or paramidline osseous defect(s)
IMAGING
• Partial or complete absence of posterior C1 arch
○ Osseous defect may be midline or paramidline
○ Partial agenesis may be unilateral or bilateral
TOP DIFFERENTIAL DIAGNOSES
• Normal immature ossification of cartilaginous posterior C1
Congenital and Genetic Disorders
arch
PATHOLOGY
• Commonly isolated anomaly; seen infrequently in
conjunction with anterior C1 ring, other CVJ anomalies
○ Posterior C1 arch deficiency 10x more common than
anterior arch defect
• Currarino classification
(Left) Axial bone CT
demonstrates complete
absence of the posterior C1
ring . There is abnormal
formation of the anterior C1
ring with 3 dysplastic anterior
ring ossification centers st
instead of the usual 1
ossification center. (Right)
Axial bone CT shows failure of
fusion of the right and left C1
hemirings, resulting in a split
atlas . There is near
complete lack of formation of
the posterior ring with only a
small ossicle near the
posterior midline ſt.
○ Type A: Median clefts of posterior C1 arch
○ Type B: Unilateral posterior arch defect
○ Type C: Bilateral posterior arch defects
○ Type D: Absent posterior arch + present posterior
tubercle
○ Type E: Total agenesis of posterior arch including
tubercle
CLINICAL ISSUES
• Most commonly asymptomatic, incidental finding
○ Observational management
• Expectant treatment directed toward symptomatic
associated anomalies
DIAGNOSTIC CHECKLIST
• Posterior C1 ring rachischisis usually incidental finding
• Generally stable if isolated, requires no specific treatment
92
(Left) Axial CECT shows failure
of fusion of the right and left
C1 hemirings, resulting in a
split atlas. The midline
posterior C1 arch ſt gap is
larger than the anterior arch
cleft st. (Right) Axial bone CT
depicts an asymmetric cleft ſt
through the posterior C1 ring.
The corticated margins
confirm that this represents
asymmetric development of
the posterior C1 ring, resulting
in asymmetric location of the
posterior synchondrosis,
rather than acute fracture.
Split Atlas
KEY FACTS
Congenital and Genetic Disorders
TERMINOLOGY
• Synonym: Split C1
IMAGING
• Anterior, posterior C1 arch defects → 2 C1 hemirings
○ Defects usually midline but may be paramedian
○ Wider gaps suggest independent lateral migration of C1
hemirings, instability
• ± hypoplastic ring → spinal canal stenosis, cord
compression, myelomalacia, syrinx
TOP DIFFERENTIAL DIAGNOSES
• Jefferson C1 fracture
• Isolated anterior C1 arch defect
• Isolated posterior C1 arch defect
PATHOLOGY
• Simultaneous hypoplasia of C1 hypochordal bow, lateral C1
sclerotomes → combined anterior, posterior C1 arch
defects
○ Ring defects usually contain fibrous connective tissue,
not cartilage
○ Connective tissue more fragile than cartilage →
hemirings may split
CLINICAL ISSUES
• May be asymptomatic in adult
○ Simple bifid atlas (minimal gaps) usually asymptomatic,
discovered incidentally
• Prognosis largely depends on severity of ring defects, CVJ
stability, C1 ring hypoplasia
• Split atlas with larger arch defects more likely to be
unstable → neck pain, torticollis, myelopathy
DIAGNOSTIC CHECKLIST
• Split atlas is rare congenital anomaly
○ Stability depends on anomaly severity, transverse
atlantal ligament integrity
• Search for associated skull base, CVJ anomalies
(Left) Axial bone CT
demonstrates short AP
dimension of the hypoplastic
C1 ring as well as a split ring
configuration characterized by
midline defects ſt in both
anterior and posterior rings.
The dens is thickened and
dysplastic. (Right) Sagittal
bone CT in patient with a split
C1 ring shows mildly dysplastic
dens formation and
abnormal hypoplastic C1 ring
ſt, resulting in severe spinal
canal stenosis. Note
associated C2/3 segmentation
failure st.
(Left) Axial bone CT reveals
large midline osseous defects
ſt in both the anterior and
posterior C1 rings. The wide
gaps suggest instability.
(Right) Coronal bone CT shows
congenital scoliosis and
extensive cervicothoracic
vertebral segmentation
failure. The C1 lateral masses
ſt are independently
displaced laterally in opposite
directions, permitted by the
split atlas configuration. This
is a very unstable
configuration necessitating
surgical fusion.
93
Odontoid Hypoplasia/Aplasia
KEY FACTS
TERMINOLOGY
• Congenital small or absent odontoid process
IMAGING
• Reduced size of odontoid process
○ Odontoid process is small, blunted
○ Hypoplasia > > aplasia
• ± enlargement of anterior C1 ring
• ± spinal cord myelomalacia, syringomyelia
TOP DIFFERENTIAL DIAGNOSES
• Os odontoideum
Congenital and Genetic Disorders
• Odontoid C2 fracture
• Surgical odontoid resection
PATHOLOGY
• Developmental abnormality
○ More common in patients with skeletal dysplasias,
trisomy 21
(Left) Lateral cervical
radiograph demonstrates a
congenital hypoplastic
odontoid process ſt with
normal C1/2 alignment. The
anterior C1 ring is mildly
enlarged, likely compensatory
hypertrophy. No other cervical
spine abnormalities were
present. (Right) Lateral
cervical radiograph reveals
mild congenital hypoplasia of
the dens process ſt. There is
compensatory enlargement of
the anterior C1 ring .
Craniovertebral junction
alignment is normal, and no
additional anomalies are
present.
• Generally nonfamilial, although some reports of autosomal
dominant inheritance
• Associated anomalies: Segmentation failure, CVJ dynamic
instability
• Status of transverse atlantal ligament (TAL), other
stabilizing ligaments variable
CLINICAL ISSUES
• Most commonly asymptomatic
• Symptomatic patients report neck pain, myelopathy
○ Variable depending on severity, presence of dynamic
instability, other associated anomalies
• Asymptomatic patients may be amenable to expectant
observation
DIAGNOSTIC CHECKLIST
• More common in skeletal dysplasias, trisomy 21
• Severity, status of TAL, & associated anomalies determine
CVJ stability
94
(Left) Sagittal CECT
(spondylometaphyseal
dysplasia) confirms odontoid
process hypoplasia ſt and
hypoplastic C1 ring, resulting
in cervical canal stenosis. The
anterior atlas arch is
cartilaginous, representing
abnormal delayed ossification.
(Right) Sagittal T2WI MR
(neurenteric cyst, st)
demonstrates congenital CVJ
osseous anomalies, including a
short, dysplastic odontoid
process ſt. The anterior C1
ring is anteriorly displaced,
reflecting atlantoaxial
instability.
C1 Dysmorphism/Hypoplastic Arch
KEY FACTS
Congenital and Genetic Disorders
TERMINOLOGY
• Synonyms: Hypoplastic C1, hypoplastic atlas
IMAGING
• Hypoplastic posterior C1 ring with decreased AP dimension
of central canal
○ Posterior C1 ring anteriorly positioned on midline lateral,
sagittal imaging
• May be associated with spinal cord compression,
myelomalacia, syringomyelia, other CVJ osseous anomalies
TOP DIFFERENTIAL DIAGNOSES
• Posterior arch rachischisis
• Split atlas
• Atlantoaxial instability
• Achondroplasia
PATHOLOGY
• Hypoplasia of complete posterior arch secondary to
premature fusion of cartilaginous neurocentral
synchondrosis, which leads to spinal canal stenosis at C1
level
○ Less common than atlas arch clefts and defects
• Associated with skull-base osseous anomalies, Klippel-Feil
spectrum, skeletal dysplasias
CLINICAL ISSUES
• May be asymptomatic
• Symptomatic patients present with transient quadriparesis,
myelopathy, syrinx
DIAGNOSTIC CHECKLIST
• C1 ring hypoplasia relatively uncommon
○ Less common than C1 arch clefts, defects
• Associated with Klippel-Feil spectrum, skeletal dysplasias
(Left) Sagittal T2WI MR
(VACTERL) demonstrates
moderately severe central
spinal canal stenosis at the C1
level secondary to C1 ring ſt
hypoplasia. There is subtle
spinal cord T2 hyperintense
signal and volume loss at that
level, indicating myelomalacia.
(Right) Axial T1WI MR
(VACTERL) confirms
moderately severe central
canal stenosis related to C1
ring hypoplasia ſt. The
stenosis is usually most
pronounced in the
anteroposterior dimension, as
demonstrated in this patient.
(Left) Sagittal T2WI MR
(Klippel-Feil syndrome) shows
dysplastic formation of the
dens as well as an
abnormal hypoplastic C1 ring
ſt, resulting in severe canal
narrowing, spinal cord
compression, and focal
syringomyelia at the C1/2
level. (Right) Sagittal bone CT
confirms thickened dysplastic
appearance of the dens
and C1 ring ſt, with the
hypoplastic posterior C1 ring
severely narrowing the central
spinal canal. There is also
segmentation failure at C2/3
st.
95
Chiari 1
KEY FACTS
TERMINOLOGY
• Synonyms: Chiari 1 malformation (CM1), Arnold-Chiari 1
malformation
IMAGING
• Pointed cerebellar tonsils extend ≥ 5 mm below foramen
magnum ± syringohydromyelia, scoliosis, hydrocephalus
TOP DIFFERENTIAL DIAGNOSES
• Normal low-lying tonsils below foramen magnum
• Acquired tonsillar herniation (acquired Chiari 1)
Congenital and Genetic Disorders
PATHOLOGY
• Etiology not fully understood
○ Postulated mechanisms include hydrodynamic theory
and posterior fossa underdevelopment theory
• May present as isolated finding or in conjunction with
syndromic (4th occipital sclerotome) or nonsyndromic skull
base and CVJ anomalies
(Left) Sagittal graphic
demonstrates pointed peg-like
tonsils extending below the
foramen magnum, elongating
the normally positioned 4th
ventricle. (Right) Sagittal T1WI
MR shows the normal position
and appearance of the 4th
ventricle. The fastigium is
in normal position, helping to
distinguish from Chiari 2
malformation. There is inferior
displacement of the ectopic
cerebellar tonsils ſt through
the foramen magnum with
ventral spinal cord
displacement.
CLINICAL ISSUES
• Up to 50% of CM1 asymptomatic
○ Surgical treatment for asymptomatic patients
controversial
• Symptomatic patients
○ Surgical goal is restoration of normal CSF flow at
foramen magnum
○ Posterior fossa decompression and resection of
posterior C1 arch ± duraplasty, cerebellar tonsil resection
• Clinical CM1 syndrome: Headache, pseudotumor-like
episodes, Ménière disease-like syndrome, lower cranial
nerve and spinal cord signs
DIAGNOSTIC CHECKLIST
• Tonsillar herniation > 12 mm usually symptomatic
• Probably not clinically significant CM1 unless tonsils > 5 mm
&/or pointed
96
(Left) Sagittal T2WI MR shows
the normal position and
appearance of the 4th
ventricle. The fastigium is
in normal position, helping to
distinguish from the Chiari 2
malformation. Note inferior
displacement of the ectopic
elongated cerebellar tonsils
ſt through the foramen
magnum that produces mass
effect on the upper cervical
spinal cord. (Right) Axial T2WI
MR shows inferior
displacement of the ectopic
cerebellar tonsils ſt through
the foramen magnum with
crowding of the foramen
magnum.
Complex Chiari
KEY FACTS
Congenital and Genetic Disorders
TERMINOLOGY
• Complex Chiari malformation (CCM),Chiari 1.5
IMAGING
• Cerebellar tonsillar herniation with low obex, dorsal
medullary "bump"
○ "Bump" thought to represent aberrant clava, used as
marker for cervicomedullary junction
○ Abnormal tonsillar "pistoning" motion, reduced CSF flow
around foramen magnum and cerebellar tonsils
• ± syringohydromyelia, ventral cervicomedullary
compression
• ± odontoid retroflexion, small posterior fossa, clival
anomalies, platybasia
TOP DIFFERENTIAL DIAGNOSES
• Chiari 1 malformation
• Chiari 2 malformation
PATHOLOGY
• Medullary pyramid decussation anatomic border between
spinal cord, medulla oblongata
○ Normal obex level is 10-12 mm above foramen magnum
○ Obex displaced to or below foramen magnum level in
CCM patients
CLINICAL ISSUES
• Headaches, myelopathy, bulbar symptoms, lethargy, failure
to thrive
DIAGNOSTIC CHECKLIST
• Consider CCM in context of cerebellar tonsillar herniation +
low obex, dorsal medullary "bump"
• CCM considered subgroup of Chiari 1 malformation with
more severe clinical phenotype
(Left) Sagittal T1WI MR shows
classic features of a complex
Chiari malformation, including
marked cerebellar tonsil
ectopia ſt and inferior
displacement of the obex .
The 4th ventricle is in normal
position. (Right) Sagittal T2WI
MR reveals characteristic
tonsillar ectopia ſt and
inferior displacement of the
cervicomedullary junction,
marked by position of the
obex below the foramen
magnum. There is also mild
retroflexion of the odontoid
process and mild clivus st
foreshortening.
(Left) Sagittal T2WI MR
(different patient) shows a
prominent obex and
pointed, ectopic cerebellar
tonsils ſt. The odontoid
process is retroflexed, and
the clivus st is foreshortened,
with a reduced craniocervical
angle with platybasia. (Right)
Sagittal T2WI MR (different
patient) reveals striking
odontoid retroflexion. Note
also severe cerebellar tonsillar
ectopia ſt extending
inferiorly to the C3 level and
cervical syringohydromyelia
. The prominent, inferiorly
displaced obex confirms a
complex Chiari malformation.
97
Chiari 2
KEY FACTS
TERMINOLOGY
• Synonyms: Chiari 2 malformation 2, Chiari II
• Complex hindbrain malformation
• Virtually 100% associated with neural tube closure defect,
usually lumbar myelomeningocele
IMAGING
• Cerebellum "wraps" around medulla and "towers" through
incisura, with "beaked" tectum and heart-shaped midbrain
• Virtually 100% have neural tube closure defect
TOP DIFFERENTIAL DIAGNOSES
Congenital and Genetic Disorders
• Chiari 1 malformation
• Chiari 3 malformation
• Intracranial CSF hypotension
• Severe, chronic shunted hydrocephalus (congenital)
(Left) Sagittal graphic of the
posterior fossa and upper
cervical spine demonstrates
characteristic findings of
Chiari 2 malformation,
including callosal dysgenesis
, tectal beaking ſt, small
posterior fossa, vermian
ectopia , and medullary
kinking . (Right) Sagittal
T1WI MR reveals
characteristic Chiari 2
malformation findings. Note
tectal beaking ſt and vermian
displacement through the
foramen magnum, large
massa intermedia st, and
dysplastic corpus callosum .
PATHOLOGY
• Secondary to sequelae of CSF leakage through open spinal
dysraphism during gestation (4th fetal week)
• Methylenetetrahydrofolate reductase (MTHFR) mutations
→ abnormal folate metabolism
• Spine- and brain/skull-associated anomalies common
CLINICAL ISSUES
• Chiari 2 malformation most common cause of death in
myelomeningocele patients
○ Brainstem compression/hydrocephalus, intrinsic
brainstem "wiring" defects
DIAGNOSTIC CHECKLIST
• Towering cerebellum, downward vermian displacement, ±
brainstem compression diagnostic for Chiari 2
98
(Left) Sagittal T2WI MR
confirms characteristic
findings of Chiari 2
malformation including tectal
beaking ſt, vermian
displacement through the
foramen magnum ,
"towering cerebellum" st,
large massa intermedia ,
and dysplastic corpus callosum
. (Right) Sagittal T2WI MR
depicts marked vermian
ectopia and a prominent
medullary kink st positioned
lower than typically seen at
the C4 level. Note also the
dysplastic "beaked" tectum ſt
and prominent massa
intermedia .
Chiari 3
KEY FACTS
Congenital and Genetic Disorders
TERMINOLOGY
• Chiari 3 malformation
• Synonyms: Chiari III, rhombencephalocele
IMAGING
• Low occipital or high cervical meningoencephalocele
containing cerebellum ± brainstem, meninges, vessels, CSF
• Midline bone defect within supraoccipital bone, opisthion
TOP DIFFERENTIAL DIAGNOSES
• Isolated occipital encephalocele
• Other occipital encephaloceles
○ Iniencephaly
○ Syndromic occipital encephalocele
PATHOLOGY
• Severity classified by sac contents
• Cephalocele contents: Meninges, cerebellum, brainstem ±
cervical cord, occipital poles, vasculature
○ Disorganized (neuronal migration anomalies, cortical
dysplasias) and gliotic brain tissue
○ Lining of sac may show gray matter heterotopias
• Associated abnormalities: Corpus callosum anomalies, gray
matter heterotopia, syringohydromyelia, tethered cord
CLINICAL ISSUES
• Microcephaly, severe developmental delay, spasticity,
hypotonia, seizures
• Mechanical brainstem traction, respiratory deterioration,
lower cranial nerve dysfunction
DIAGNOSTIC CHECKLIST
• Occipitocervical cephalocele containing cerebellum ±
brainstem in conjunction with C1-C2 spina bifida = Chiari 3
malformation
• Distinct malformation; not just Chiari 2 malformation with
encephalocele
(Left) Sagittal graphic shows
typical Chiari 3 features of
Chiari 2 plus meningocele.
Note callosal hypoplasia ,
prominent massa intermedia
, beaked tectum st, and
inferiorly displaced cerebellar
tissue ſt. There is a
supraoccipital bone defect
with protruding skin-covered
cephalocele containing
gliotic tissue and meninges.
(Right) Sagittal T2WI MR
shows a large cephalocele
containing gliotic cerebellum
and meninges. Tectal beaking
st and tonsillar descent ſt
confirmed Chiari 3
malformation.
(Left) Sagittal T1WI MR shows
a large meningoencephalocele
composed of meninges, CSF,
cerebellum ſt, brainstem ,
and upper cervical spinal cord
herniated through a bone
defect in the lower occiput
and upper cervical spine.
(Right) Sagittal MRV
demonstrates typical venous
abnormalities of Chiari 3. The
straight sinus ſt and vein of
Galen are severely hypoplastic.
Large occipital sinuses ,
rather than transverse sinuses,
are present.
99