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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_6009_Библиотеки_им_академика_М_И_Перельмана.pdf
Cranial Settling
DIFFERENTIAL DIAGNOSIS
Common
• Cranial Settling
• Basilar Invagination
• Basilar Impression
• Platybasia
Differential Diagnosis
ESSENTIAL INFORMATION
Key Differential Diagnosis Issues
• Cranial Settling
○ Defined as subtype of basilar impression occurring in
rheumatoid arthritis (RA)
– Cranial settling diagnosed when 2 conditions are met:
(1) Superior aspect of dens is even with or above
McRae line (foramen magnum), unless there is
marked dental erosion, and (2) anterior arch of C1
assumes an abnormally low position in relation to C2
(cranial settling is also known as vertical atlantoaxial
subluxation)
– Skull and C1 ring move as unit with respect to C2 and
rest of spine
– Shows classic upward translocation of odontoid with
low C1 ring due to transverse ligament incompetence
○ Erosive changes of atlantal lateral masses result in
downward telescoping of atlas onto axis body
– Anterior displacement of atlantal posterior arch
– Ventral and dorsal cervicomedullary compression
○ Clark station is determined by dividing odontoid process
into 3 equal parts in sagittal plane
– If anterior ring of atlas is level with middle 3rd (station
II) or caudal 3rd (station III) of odontoid process, basilar
impression is present
○ McGregor line is line drawn on midline image from hard
palate to base of occiput
– Cranial settling of occiput is defined as migration of
odontoid more than 4.5 mm above McGregor line
○ Redlund-Johnell measurement is distance between
midpoint of caudal end plate of C2 to McGregor line
(value of < 34 mm in men and 29 mm in women is
considered abnormal)
• Basilar Invagination
○ Developmental anomaly of craniovertebral junction
where odontoid process has abnormal relationship to
foramen magnum (prolapse)
○ Has been categorized by absence (type 1) or presence
(type 2) of Chiari malformation
• Basilar Impression
○ Acquired abnormality of odontoid position with respect
to foramen magnum resulting from bone softening or
ligamentous laxity at skull base
○ 1 of 3 directional instabilities that occur in RA
– Other 2 instabilities: Atlantoaxial subluxation and
subaxial subluxation
• Platybasia
○ Abnormal flattening of skull base
○ Determined through lines from nasion to dorsum sellae
and from dorsum sella to basion
○ Generally associated with abnormalities such as Chiari
malformations but not clinically significant
SELECTED REFERENCES
1. Krauss WE et al: Rheumatoid arthritis of the craniovertebral junction.
Neurosurgery. 66(3 Suppl):83-95, 2010
2. Mouchaty H et al: Craniovertebral junction lesions: our experience with the
transoral surgical approach. Eur Spine J. 18 Suppl 1:13-9, 2009
3. Smoker WR et al: Imaging the craniocervical junction. Childs Nerv Syst.
24(10):1123-45, 2008
4. Caird J et al: Preoperative cervical traction in cases of cranial settling with
halo ring and Mayfield skull clamp. Br J Neurosurg. 19(6):488-9, 2005
5. Goel A et al: Atlantoaxial joint distraction for treatment of basilar
invagination secondary to rheumatoid arthritis. Neurol India. 53(2):238-40,
2005
6. Nannapaneni R et al: Surgical outcome in rheumatoid Ranawat Class IIIb
myelopathy. Neurosurgery. 56(4):706-15; discussion 706-15, 2005
7. Goel A et al: Craniovertebral realignment for basilar invagination and
atlantoaxial dislocation secondary to rheumatoid arthritis. Neurol India.
52(3):338-41, 2004
8. Nguyen HV et al: Rheumatoid arthritis of the cervical spine. Spine J. 4(3):329-
34, 2004
400
Cranial Settling Cranial Settling
(Left) Sagittal NECT shows
cranial settling with upward
translocation of the odontoid
process ſt. There are also
dens erosions st and
increased atlantodental
interval . Note the low
position of C1 ring relative to
the C2 body. (Right) Sagittal
T2WI MR study shows
compression of the cord at the
C1 level due to cranial settling
and atlantodental instability
with ventral and dorsal
compression ſt.
Cranial Settling
Cranial Settling Cranial Settling
Basilar Invagination Basilar Invagination
Differential Diagnosis
(Left) Sagittal NECT shows
rheumatoid cranial settling
with upward translocation of
the odontoid process ſt into
the foramen magnum and
abnormal relationship
between the skull base and
C1. There are typical erosive
changes in the odontoid
process and subaxial erosions.
Note the caudal position of C1
relative to C2 body . (Right)
Coronal NECT shows
rheumatoid cranial settling
with upward prolapse of the
odontoid into the foramen
magnum and collapse of the
lateral masses of C1 .
(Left) Sagittal T2WI MR shows
Chiari 1 malformation with
inferior descent of the
abnormally pointed ectopic
cerebellar tonsils through
the foramen magnum. The
odontoid process st is also
retroflexed, and the clivus is
mildly hypoplastic. (Right)
Sagittal T2WI MR shows
severe Chiari 1 malformation
with contributory
craniovertebral segmentation
anomalies and syringomyelia.
There is striking odontoid
process retroflexion ſt and
upward positioning.
Basilar Impression Platybasia
(Left) Sagittal T1WI shows the
typical pattern of basilar
impression with Paget disease
due to bone softening of the
skull base, causing relative
upward prolapse of the
odontoid process ſt. (Right)
Sagittal T1WI shows basilar
invagination in a patient with
Chiari 2 malformation who
also has platybasia ſt.
401
Platybasia
DIFFERENTIAL DIAGNOSIS
Common
• Chiari 1 Malformation
• Chiari 2 Malformation
• Klippel-Feil Spectrum
• Paget Disease
• Osteomalacia
Differential Diagnosis
• Osteogenesis Imperfecta
Less Common
• 22q11.2 Deletion Syndrome
ESSENTIAL INFORMATION
Key Differential Diagnosis Issues
• Platybasia is defined as abnormal flattening of skull base
○ Occurs in various congenital disorders but usually as
secondary or associated finding; typically has no clinical
impact
– Often associated with basilar invagination
○ Associated with rise in odontoid and craniocervical
junction above palatine line, which may favor transnasal
approach to skull base
• Variable methods of measurement
○ Angle at junction of lines from nasion to central aspect of
pituitary fossa and from pituitary fossa to basion on plain
films
– Normal: 130°-140° (Welcher basal angle)
– Abnormal: > 140° (flattening)
○ Angle at junction of lines from nasion to dorsum sella
and from dorsum sella to basion (along posterior margin
of clivus) on MR images
– Adults: 129° ± 6°; children: 127° ± 5°
Helpful Clues for Common Diagnoses
• Chiari 1 Malformation
○ Key facts: Mismatch between posterior fossa size and
cerebellar tissue volume
○ Imaging: Tonsils project ≥ 5 mm below foramen
magnum
• Chiari 2 Malformation
○ Key facts: Nearly 100% have neural tube closure defect
○ Imaging: Small posterior fossa, "notched" clivus, low-lying
tentorium
• Klippel-FeilSpectrum
○ Key facts: Congenital spinal malformation characterized
by segmentation failure of ≥ 2 cervical vertebrae ±
thoracic or lumbar segmentation failure
○ Imaging: Single- or multilevel congenital cervical
segmentation and fusion anomalies
– Associated abnormalities include odontoid dysplasia,
basilar impression, C1 assimilation, occipitocervical
instability
• Paget Disease
○ Key facts: Often asymptomatic involvement of skull base
(often only site of involvement); M > F
○ Imaging: May be multifocal disease with mixed sclerotic-
lytic pattern
– Expands bone; results in cotton wool appearance
• Osteomalacia
○ Key facts: Abnormal mineralization in trabecular and
cortical bone
○ Imaging: Deformities due to bone softening: Basilar
impression, vertebral endplate compressions, scoliosis
• Osteogenesis Imperfecta
○ Key facts: Genetic disorder of type I collagen resulting in
bone fragility
○ Imaging: Severe osteopenia, vertebral fractures,
kyphoscoliosis
Helpful Clues for Less Common Diagnoses
• 22q11.2 Deletion Syndrome
○ Key facts: OMIM #188400 (DiGeorge syndrome)
Imaging: Platybasia and upper cervical spine anomalies
○
common (dysplastic atlas in 75%)
SELECTED REFERENCES
1. Dasenbrock HH et al: Endoscopic image-guided transcervical
odontoidectomy: outcomes of 15 patients with basilar invagination.
Neurosurgery. 70(2):351-9; discussion 359-60, 2012
402
Chiari 1 Malformation Chiari 1 Malformation
(Left) Sagittal T1W MR in a
patient with atlantooccipital
assimilation and Chiari 1
malformation shows
retroflexed odontoid ſt and
low-lying tonsils that are pegshaped . There is mild
associated flattening of the
skull base. (Right) Sagittal
T2W MR of Chiari 1
malformation shows the
typical peg-shaped
appearance of cerebellar
tonsils ſt, which descend to
the level of C1 arch. The 4th
ventricle is normal in position.
Mild platybasia is present st.
Platybasia
Chiari 2 Malformation Klippel-Feil Spectrum
Klippel-Feil Spectrum Klippel-Feil Spectrum
Differential Diagnosis
(Left) Sagittal T1WI in a
patient with Chiari 2
malformation shows
flattening of the Welcher
basal angle ſt and basilar
invagination with upward
prolapse of the odontoid
process into the foramen
magnum. (Right) Sagittal
T2WI MR in a child with
Klippel-Feil spectrum and
basilar invagination shows
flattening of the skull base ſt
and upward migration of the
odontoid process into the
foramen magnum with cord
compression.
(Left) Sagittal T1WI MR in a
patient with C0-C1
assimilation, retroflexed
odontoid, and C2-C3 fusion
shows associated flattening of
the skull base angle ſt and
short, truncated clivus .
(Right) Sagittal T1WI MR
shows severe flattening of the
Welcher basal angle ſt in a
patient with multiple
vertebral segmentation
anomalies.
Osteogenesis Imperfecta Osteogenesis Imperfecta
(Left) Sagittal T2WI MR shows
basilar impression in
osteogenesis imperfecta with
platybasia ſt and upward
displacement of the odontoid
process into the foramen
magnum, producing ventral
cervicomedullary compression.
(Right) Sagittal T1WI MR
shows severe basilar
impression related to
osteogenesis imperfecta with
the odontoid process
projecting into the foramen
magnum, producing ventral
cervicomedullary compression.
403
Intrinsic Skull Base Lesion
DIFFERENTIAL DIAGNOSIS
Common
• Metastasis, Skull Base
• Fibrous Dysplasia, Skull Base
• Paget Disease, Skull Base
• Chordoma, Clivus
• Multiple Myeloma, Skull Base
Differential Diagnosis
• Plasmacytoma, Skull Base
• Chondrosarcoma, Skull Base
• Pneumatization Arrest, Sphenoid
Less Common
• Langerhans Histiocytosis, Skull Base
• Arachnoid Granulations, Dural Sinuses
• Osteomyelitis, Skull Base
• Meningioma, Skull Base
Rare but Important
• Giant Cell Tumor, Skull Base
• Cephalocele, Skull Base
• Ecchordosis Physaliphora
• Pseudotumor, Skull Base
ESSENTIAL INFORMATION
Key Differential Diagnosis Issues
• Lesion may be focal, diffuse, localized, or part of systemic
disease
• Variable presentation of skull base lesion
○ Headache, cranial neuropathy
○ May be incidental imaging finding
• Imaging strategy
○ CT and MR often complementary
Helpful Clues for Common Diagnoses
• Metastasis, Skull Base
○ Key facts
○ Imaging
• Fibrous Dysplasia, Skull Base
○ Key facts
○ Imaging
• Paget Disease, Skull Base
○ Key facts
404
– CT best demonstrates aggressive or benign bone
features
– MR may have characteristic signal intensity or
enhancement
– Central skull base is most frequent site
– Most often prostate, breast, and lung carcinoma
– CT: Lytic, destructive, or sclerotic
– MR: Variable signal, usually enhances
– Benign expansile bone anomaly
– Prone to enlarge during childhood
– CT: Characteristic ground-glass appearance; may
narrow foramina and fissures
– MR: Heterogeneous, mass-like lesion
– T2: Ground-glass hypointense, lucent hyperintense,
variable enhancement
– Chronic bone disorder with abnormal bone
breakdown and formation
○ Imaging
– CT: Sclerotic expansion of bone with cotton wool
texture ± lytic areas
– MR: T2 mainly low, lytic areas bright
• Chordoma, Clivus
○ Key facts
– Benign but locally aggressive primary tumor of
notochord remnants
– From sphenooccipital synchondrosis
○ Imaging
– CT: Lytic destructive midline sphenoid mass ± irregular
bone spicules
– MR: Characteristic high T2 signal, heterogeneous
enhancement
• Multiple Myeloma, Skull Base
○ Key facts
– Focal mass of malignant plasma cells
– More frequently seen in calvarium
○ Imaging
– CT
□ Multiple well-defined lytic lesions
• Plasmacytoma, Skull Base
○ Key facts
– Isolated tumor of malignant plasma cells
○ Imaging
– CT: Solitary lesion, bony lysis
– MR: T2 intermediate signal; moderate enhancement
• Chondrosarcoma, Skull Base
○ Key facts
– Malignant cartilaginous neoplasm
– Arises from petroclival synchondrosis
○ Imaging
– CT: Destructive mass at junction of sphenoid and
temporal bones
– Arcs and whorls of calcification
– MR: T2 bright, intense enhancement
• Pneumatization Arrest, Sphenoid
○ Key facts
– Incidental lesion of basisphenoid
○ Imaging
– CT: Nonexpansile with sclerotic margin
– Contains fat and curvilinear calcification
– MR: Heterogeneous, often focal T1 fat
Helpful Clues for Less Common Diagnoses
• Langerhans Histiocytosis, Skull Base
○ Key facts
– Proliferation of bone marrow-derived Langerhans
cells and eosinophils
– Skull base involvement more often with multifocal or
acute disseminated forms
○ Imaging
– Nonspecific destructive soft tissue mass
• Arachnoid Granulations, Dural Sinuses
○ Key facts
– Usually incidental imaging finding
○ Imaging
– More numerous around dural sinuses
– CT: Small, well-defined "pits" in skull base
– MR: Often subtle, focal T2 hyperintensity
Intrinsic Skull Base Lesion
• Osteomyelitis, Skull Base
○ Key facts
– Primary bone infection, acute or chronic
○ Imaging
– CT: Permeative lytic when acute; chronic may be lytic
or lytic-sclerotic
– MR: Marrow replacement, enhancement; often
extensive involvement of dura
• Meningioma, Skull Base
○ Key facts
– Dural-based, benign extraaxial tumor
– May occur as intraosseous lesion
○ Imaging
– CT: Bony changes may be hyperostosis, erosion, or
permeative destruction
– MR: Bone and thick dura enhance
Helpful Clues for Rare Diagnoses
• Giant Cell Tumor, Skull Base
○ Key facts
– Benign long bone tumor
– Skull base
□ Sphenoid and temporal bones
– Can be locally aggressive &/or recur
○ Imaging
– CT: Destructive mass with focally interrupted, thinned
cortical shell
– MR: Scant matrix, larger lesions more heterogeneous,
marked enhancement
• Cephalocele, Skull Base
○ Key facts
– Skull base defect with protrusion of meninges ±
neural tissue
○ Imaging
– CT: Focal bone defect
– MR: Dura, CSF, ± neural elements
• Ecchordosis Physaliphora
○ Key facts
– Notochordal remnant exophytic from dorsal aspect of
clivus
Differential Diagnosis
○ Imaging
– CT: Soft tissue density lesion
– MR: T1 low, T2 high, no enhancement
• Pseudotumor, Skull Base
○ Key facts
– Idiopathic inflammatory lesion
– Inflammatory cells and variable fibrosis
○ Imaging
– CT: Soft tissue mass, permeative bone
– MR: Enhancing infiltrative process, T2 hypointense, T1
iso- to hypointense
SELECTED REFERENCES
1. Mathur A et al: Imaging of skull base pathologies: Role of advanced
magnetic resonance imaging techniques. Neuroradiol J. 28(4):426-37, 2015
2. Walcott BP et al: Chordoma: current concepts, management, and future
directions. Lancet Oncol. 13(2):e69-76, 2012
3. Adamek D et al: Ecchordosis physaliphora: a case report and a review of
notochord-derived lesions. Neurol Neurochir Pol. 45(2):169-73, 2011
4. Alonso-Basanta M et al: Proton beam therapy in skull base pathology.
Otolaryngol Clin North Am. 44(5):1173-83, 2011
5. Chamoun RB et al: Management of skull base metastases. Neurosurg Clin N
Am. 22(1):61-6, vi-ii, 2011
6. Koutourousiou M et al: Skull base chordomas. Otolaryngol Clin North Am.
44(5):1155-71, 2011
7. Lui YW et al: Sphenoid masses in children: radiologic differential diagnosis
with pathologic correlation. AJNR Am J Neuroradiol. 32(4):617-26, 2011
8. Nuñez S et al: Midline congenital malformations of the brain and skull.
Neuroimaging Clin N Am. 21(3):429-82, vii, 2011
9. Scholz M et al: Skull base approaches in neurosurgery. Head Neck Oncol.
2:16, 2010
10. Kastrup O et al: Neuroimaging of infections of the central nervous system.
Semin Neurol. 28(4):511-22, 2008
11. Welker KM et al: Arrested pneumatization of the skull base: imaging
characteristics. AJR Am J Roentgenol. 190(6):1691-6, 2008
12. Dubrulle F et al: Extension patterns of nasopharyngeal carcinoma. Eur
Radiol. 17(10):2622-30, 2007
13. Noël G et al: Chondrosarcomas of the base of the skull in Ollier's disease or
Maffucci's syndrome--three case reports and review of the literature. Acta
Oncol. 43(8):705-10, 2004
14. St Martin M et al: Chordomas of the skull base: manifestations and
management. Curr Opin Otolaryngol Head Neck Surg. 11(5):324-7, 2003
15. Wallace RC et al: Posttreatment imaging of the skull base. Semin Ultrasound
CT MR. 24(3):164-81, 2003
Metastasis, Skull Base Fibrous Dysplasia, Skull Base
(Left) Axial T1WI MR in a
patient with a history of lung
cancer and a new right CNXII
palsy shows focal loss of
bright marrow signal at the
right skull base ſt with
abnormal tissue around the
hypoglossal canal . (Right)
Axial bone CT demonstrates
that the greater wing ſt has
the characteristic ground-glass
appearance with areas of
dense sclerosis and other
areas of greater lucency st.
Note the narrowed vidian
canal .
405
(Left) Axial bone CT shows a
diffuse cotton wool
appearance of the entire skull
base with expansion of the
squamous temporal bone ſt,
petrous apex st, and occipital
bone . Note also the stapes
Differential Diagnosis
prosthesis on the right ,
which was placed for
conductive hearing loss.
(Right) Axial T2WI MR shows
an expansile, hyperintense
mass ſt arising in the clivus
and eroding the posterior
clival cortex st. The mass
otherwise has more benign,
well-defined contours as it
extends anteriorly to involve
the longus capitis muscles.
(Left) Axial bone CT shows
multiple tiny lytic lesions ſt in
the skull base with sharply
demarcated borders. Note the
additional lesion in the
occipital bone st. Lesions of
this size are easily overlooked,
especially without a bone
algorithm CT. (Right) Axial
T2WI FS MR reveals a large
central skull base mass ſt,
which expands bone and
appears to extend laterally to
the cavernous sinuses. The
mass is homogeneous and has
intermediate signal intensity.
Intrinsic Skull Base Lesion
Paget Disease, Skull Base Chordoma, Clivus
Multiple Myeloma, Skull Base Plasmacytoma, Skull Base
406
Chondrosarcoma, Skull Base Chondrosarcoma, Skull Base
(Left) Axial T2WI MR through
the skull base demonstrates a
markedly high signal intensity
tumor ſt involving the right
petrous apex and extending
into the cerebellopontine
angle cistern. The location
suggests chondrosarcoma
arising from petroclival
synchondrosis. (Right) Axial
bone CT in a younger patient
shows a large paramedian
lytic lesion of the right
basiocciput and a petrous
bone with chondroid
calcifications ſt.
Intrinsic Skull Base Lesion
Pneumatization Arrest, Sphenoid Langerhans Histiocytosis, Skull Base
Osteomyelitis, Skull Base Meningioma, Skull Base
Differential Diagnosis
(Left) Axial bone CT reveals a
benign hyperdense
appearance of the sphenoid
body ſt and greater wing ,
mimicking fibrous dysplasia
but without the significant
expansion seen with fibrous
dysplasia. (Right) Axial CECT
shows a nonspecific but
destructive lesion ſt of the
central and anterior skull base
with invasion to the orbits
bilaterally. The tumor
surrounds carotid arteries st,
indicating involvement of
cavernous sinuses bilaterally
also. The key to the diagnosis
is that this is a pediatric
patient.
(Left) Axial T1 C+ FS MR in a
patient with Gradenigo
syndrome shows extensive
enhancement of the petrous
apex ſt but also adjacent
dural reflections. There is
involvement of middle fossa
dura and dura of internal
auditory canal st, as well as
spasm of the adjacent internal
carotid artery . (Right)
Coronal T1 C+ MR
demonstrates a
homogeneously enhancing
mass centered in the sphenoid
bone ſt. The key to the
diagnosis is the presence of
overlying dural thickening and
enhancement st.
Giant Cell Tumor, Skull Base Ecchordosis Physaliphora
(Left) Axial bone CT reveals a
thin, irregularly sclerotic
"eggshell" of the cortex.
Expansile margins suggest a
benign process. Focal areas of
bone dehiscence and
matrix calcifications are
evident st. (Right) Axial T2WI
MR demonstrates a subtle,
well-defined bilobed lesion ſt
arising from the dorsal clivus
and extending into the
prepontine cistern ,
although not causing any
deformity of the pons.
407
Foramen Magnum Mass
DIFFERENTIAL DIAGNOSIS
Common
• Acquired Tonsillar Herniation
• Chiari 1 Malformation
• Chiari 2 Malformation
• Meningioma, Clivus
• Rheumatoid Arthritis, Adult
Differential Diagnosis
• Schwannoma, Jugular Foramen
Less Common
• Chordoma, Clivus
• Ependymoma
• Chondrosarcoma, Skull Base
• Retroodontoid Pseudopannus
• Hemangioblastoma
• Calcium Pyrophosphate Dihydrate Deposition Disease
(CPPD)
• Metastasis, Skull Base
Rare but Important
• Fusiform Aneurysm, ASVD
• Fusiform Aneurysm, Non-ASVD
• Brainstem Glioma, Pediatric
• Epidermoid Cyst
• Neurenteric Cyst
ESSENTIAL INFORMATION
Key Differential Diagnosis Issues
• Foramen magnum (FM): Posterior skull base aperture in
occipital bone
○ Transmits medulla oblongata, vertebral arteries, and
CNXI
• Lesions of FM can be intraaxial, extraaxial, and bony skull
base in origin
• Cisternal magna: Skull base cistern between medulla
anteriorly and occiput posteriorly
Helpful Clues for Common Diagnoses
• Acquired Tonsillar Herniation
○ Key facts: Secondary to posterior fossa mass effect or
severe hydrocephalus
– May also be secondary to CSF leak with intracranial
hypotension ("sagging brain")
○ Imaging: Cerebellar tonsils → into FM
– Cisterna magna obliterated
– 4th ventricle obstruction → hydrocephalus
• Chiari 1 Malformation
○ Key facts
– May be incidental
○ Imaging: Small posterior fossa
– Low-lying "pegged" tonsils
– Tonsils > 5 mm below FM
• Chiari 2 Malformation
○ Key facts: Complex hindbrain malformation + lumbar
myelomeningocele
– "Beaked" tectum, "towering" cerebellum, dysgenic
corpus callosum
○ Imaging: Tonsillar ectopia
– Straw-like 4th ventricle; hydrocephalus
• Meningioma, Clivus
○ Key facts: Older, female patients
– Tends to encase and narrow vessels
○ Imaging: Enhancing dural-based mass with tails; extends
through FM when clival
– CT: High-density lesion ± Ca⁺⁺
– MR: Low signal on T2 MR
• Rheumatoid Arthritis, Adult
○ Key facts
– Inflammatory pannus in retroodontoid soft tissues
○ Imaging: Odontoid erosions common
– CT: Cranial settling in severe cases
– MR: Markedly hypointense on T2; T1 variable;
enhances
• Schwannoma, Jugular Foramen
○ Key facts: Arises from CNIX-CNXI
– Cisternal component may involve FM
– May arise primarily within FM
○ Imaging: Fusiform jugular foramen mass
– CT: Smooth enlargement of jugular foramen
– MR: Enhances; high T2 signal; intramural cysts
Helpful Clues for Less Common Diagnoses
• Chordoma, Clivus
○ Key facts: Midline mass; exophytic
– Extension into prepontine cistern "thumbs" pons
○ Imaging: Lower clival location extending to FM
– CT: Irregular destructive mass lesion within clivus
– MR: Characteristic high T2 signal; intensely enhancing
• Ependymoma
○ Key facts: Soft tumor, "squeezes out" 4th ventricle
foramina
– 2/3 infratentorial, 4th ventricle
○ Imaging: Heterogeneously enhancing 4th ventricle mass
– Inferiorly extending tumor in FM
• Chondrosarcoma, Skull Base
○ Key facts: Chondroid malignancy; petrooccipital fissure
most common
○ Imaging: 50% chondroid Ca⁺⁺ (CT)
– MR: Destructive, enhancing, T2 hyperintense tumor
– When large, affects FM
• Retroodontoid Pseudopannus
○ Key facts: Calcific debris arising posterosuperior to C1-C2
– Associated with degenerative arthritis, gout, CPPD
○ Imaging: Look for medullary or cervical cord compression
– CT: Calcifications of ligaments and within joint capsule
– MR: Low signal intensity mass behind odontoid
• Hemangioblastoma
○ Key facts: Associated with von Hippel Lindau
– 80% cerebellar hemispheres, 15% vermis, 5% medulla,
4th ventricle
○ Imaging: Cystic cerebellar mass + enhancing mural
nodule (60%)
– 40% solid mass
• Calcium Pyrophosphate Dihydrate Deposition Disease
(CPPD)
○ Key facts: Calcium pyrophosphate dihydrate deposition
disease
○ Imaging: Retroodontoid mass may cause instability ±
cervical cord compression
408
Foramen Magnum Mass
• Metastasis, Skull Base
○ Key facts: Involvement of occiput by bony metastatic
lesion
○ Imaging: Irregular bone destruction ± soft tissue mass
– When large, compresses brainstem
Helpful Clues for Rare Diagnoses
• Fusiform Aneurysm, ASVD
○ Key facts
– Aneurysm of distal vertebral artery or proximal basilar
artery
○ Imaging
– CT: Lamellated layers of calcific and noncalcific
thrombus; residual lumen
MR: Flow-related changes of lumen with varying age
–
thrombus in wall, prominent phase artifact from
aneurysm pulsation
– MRA: Shows residual lumen
– High T1 signal thrombus may be mistaken for lumen
blood flow on TOF studies
• Fusiform Aneurysm, Non-ASVD
○ Key facts: Associated with collagen vascular diseases,
other vasculopathies
○ Imaging
– CT: Shows fusiform enlargement of vessel involved
– MR: Layered thrombus or enlarged vessel
• Brainstem Glioma, Pediatric
○ Key facts: Infiltrative glioma, typically low grade,
involving medulla and pons
○ Imaging: Enlarged brainstem
– Usually no enhancement
– High T2 and FLAIR signal
– Lobulated ventral margin (exophytic)
• Epidermoid Cyst
○ Key facts: Ectodermal rest in cistern
– Cerebellopontine angle 40-50%, 4th ventricle 15-20%
○ Imaging: CSF-like, lobular, extraaxial
– DWI shows hyperintensity
– Insinuates into cisterns
– Encases nerves/vessels
Differential Diagnosis
• Neurenteric Cyst
○ Key facts: Developmental lesion resulting in intradural
midline cystic mass
○ Imaging: Smooth extraaxial mass at skull base
– Ventral to brainstem
– Iso- to hyperintense to CSF on T1
– High T2 signal; conspicuous on FLAIR
SELECTED REFERENCES
1. Lucas JW et al: Endoscopic endonasal and keyhole surgery for the
management of skull base meningiomas. Neurosurg Clin N Am. 27(2):20714, 2016
2. Jansen MH et al: Diffuse intrinsic pontine gliomas: a systematic update on
clinical trials and biology. Cancer Treat Rev. 38(1):27-35, 2012
3. Poretti A et al: Neuroimaging of pediatric posterior fossa tumors including
review of the literature. J Magn Reson Imaging. 35(1):32-47, 2012
4. Starke RM et al: Gamma knife surgery for skull base meningiomas. J
Neurosurg. 116(3):588-97, 2012
5. Walcott BP et al: Chordoma: current concepts, management, and future
directions. Lancet Oncol. 13(2):e69-76, 2012
6. Gutierrez J et al: Dolichoectasia-an evolving arterial disease. Nat Rev Neurol.
7(1):41-50, 2011
7. Ishiyama G et al: Vertebrobasilar infarcts and ischemia. Otolaryngol Clin
North Am. 44(2):415-35, ix-x, 2011
8. Khatua S et al: Diffuse intrinsic pontine glioma-current status and future
strategies. Childs Nerv Syst. 27(9):1391-7, 2011
9. Koutourousiou M et al: Skull base chordomas. Otolaryngol Clin North Am.
44(5):1155-71, 2011
10. Lee CJ et al: Treatment of vertebral disease: appropriate use of open and
endovascular techniques. Semin Vasc Surg. 24(1):24-30, 2011
11. Mattle HP et al: Basilar artery occlusion. Lancet Neurol. 10(11):1002-14, 2011
12. Oakes WJ: Chiari malformation Type I. J Neurosurg. 115(3):645; discussion
645-6, 2011
13. Fraser JF et al: Endoscopic endonasal transclival resection of chordomas:
operative technique, clinical outcome, and review of the literature. J
Neurosurg. 112(5):1061-9, 2010
14. Fangusaro J: Pediatric high-grade gliomas and diffuse intrinsic pontine
gliomas. J Child Neurol. 24(11):1409-17, 2009
15. Sievert AJ et al: Pediatric low-grade gliomas. J Child Neurol. 24(11):1397-
408, 2009
16. Johnson MD et al: New prospects for management and treatment of
inoperable and recurrent skull base meningiomas. J Neurooncol. 86(1):10922, 2008
17. Sekhar LN et al: Meningiomas involving the clivus: a six-year experience with
41 patients. Neurosurgery. 27(5):764-81; discussion 781, 1990
Acquired Tonsillar Herniation Chiari 1 Malformation
(Left) Sagittal T1WI MR
reveals acquired tonsillar
herniation ſt as a result of
intracranial hypotension with
the "slumping" midbrain
squeezing the pons inferiorly.
(Right) Sagittal T1WI MR
shows a Chiari 1 malformation
demonstrating tonsillar
herniation. The tonsils
protrude through the foramen
magnum, below an imaginary
line drawn between the basion
ſt and opisthion .
409