IMAGING OF CONGENITAL SKULL LESIONS IS A VERY RICH TOPIC TO TALK, LET’S GET A LOOK.
- A dysplasia of the cartilage bones of the skull vault.
- They lie in the thickest part of frontal, parietal & upper occipital bone.
- Commonly associated with CNS anomalies: myelomeningiocele, hydrocephalus.
In infants, disappear by 4-6 months.
Bilateral clusters of elliptical areas in which the vault is extremely thin are separated by thicker strands; some areas of the vault may be normal.
Shows that the scalloping predominantly affects the outer table.
II-Abnormalities of the Cranial Sutures:
A- Normal variation of the shape of the skull (Not pathological):
1-Dolichocephaly: longer skull in relation to width.
2-Brachycephaly: wider skull in relation to length.
3-Trigonocephaly: triangular skull due to the sharp anterior pointing of frontal bone due to premature fusion of metopic suture (in utero).
4-Bathrocephaly: square occipital bone overlapping the parietal bone at the lambdoid suture (should not be confused with traumatic lesions).
B-Premature fusion of Skull Sutures (Craniosynostosis):
- Premature fusion of a calvarial suture.
- Maybe primary or secondary to metabolic disease, bone dysplasia, hematological disorder or decreased intracranial pressure.
- Most cases are detectable at birth.
- M:F = 3:1.
- Frequency of sutural involvement: sagittal 56%, multiple 14%, unilateral coronal. 11%, bilateral coronal 11%, metopic 17% and lambdoid 1%.
Abnormally shaped head.
- Analysis of skull shape is the best radiologic clue for diagnosis.
- The resulting deformity depends on which suture is affected:
Produces a long and narrow skull (dolichocephaly or scaphocephaly).
Severe craniosynostosis of the scaphocephalic type caused by premature synostosis of only a short segment of the sagittal suture of a 2-week-old infant. A, In lateral projection, deformity resulting from the craniostenosis is clearly seen, but the sagittal suture itself is invisible (superior black arrows). Coronal (black arrows) and lambdoid sutures (white arrow) are widened. B, In frontal projection, the sagittal suture is visible in its entirety and is open except for a short segment (arrows) only a few millimeters long. Caffey's Pediatric diagnostic imaging
May be unilateral or bilateral
-if bilateral produce a short and wide/tall skull (brachycephaly or turricephaly).
-if unilateral produce lopsided skull (plagiocephalic).
produces a pointed forehead (trigonocephaly) and hypotelorism.
-if unilateral causes flattening of the occipital region (plagiocephaly)
-if bilateral, causes flattening of the entire occiput.
5-All sutures: produce sharp peaked crown (oxycephaly).
- ‘Harlequin eye’ appearance is seen with complete coronal craniosynostosis which extends to the sphenoethmoidal synchondrosis
- Cloverleaf skull (Kleeblattschadel) is caused by intrauterine premature closure of the coronal, lambdoid and sagittal sutures and is associated with lacunar skull (Luckenschadel) and brain dysgenesis or hydrocephalus.as figure below.
Rudlof - Atlas of newborn - volume III
NB: In microcephaly: small head due to premature closure of all the sutures+ primary mental defect.
- Sutural narrowing, parasutural sclerosis, sharpening of suture edges and bony bridging across the sutures.
- May only see buckling of suture with fibrous (non-bony) fusion.
Delayed growth of biparietal diameter in early pregnancy
- Strip craniectomy in cases of single craniosynostosis is for cosmetic purposes as brain growth is not impaired
- With universal craniosynostosis, strip craniectomy is mandatory to prevent complications of increased intracranial pressure and to allow brain growth.
NB: Prevent premature closure of sutures before 9 months:
– prevent mental defect.
–regain normal shape.
C-Widening of the sutures
- occurs most commonly with raised intracranial pressure.
- It is also seen with neoplastic infiltration of the sutures by, e.g., neuroblastoma, in which case the adjacent bone is often clearly eroded.
III-Abnormalities of skull base& foramen magnum:
A condition in which the base of skull appears relatively flattened
- There is an increase in the basal angle, as measured on a true lateral skull film.
- The basal angle: lies between the two lines drawn from the anterior lip of the foramen magnum and the nasion to a point at or near the tuberculum sellae: the normal range is 120–140º; when the angle exceeds 148º the base of the skull is abnormally flat.
- The term platybasia is sometimes used rather loosely to include basilar impression and basilar invagination.
- Indicates an elevation of floor of the posterior fossa.
- Commonly associated with congenital anomalies of cervical spine.
- The foramen magnum may be abnormal in shape and size.
This is a term reserved for conditions in which the margins of the foramen magnum are inverted.
it is usually developmental, but similar changes may complicate rickets, Paget’s disease or other conditions in which the bone is softened.
The following lines may be used for assessment of basilar invagination on either plain films or CT scout topogram film:
1-Chamberlain’s line: drawn on the true lateral projection of the craniocervical junction, from the posterior end of the hard palate to the posterior border of the foramen magnum. Not more than 2 mm of the odontoid process should lie above this line
.2-MacGregor’s modification: as above, but using the occipital squama as the posterior landmark when the posterior lip of the foramen is not identified with ease. This line is vitiated if the head is tilted to one side. Not more than half the odontoid should be above this line.
3-The digastric line: on the occipitofrontal projection, between the two digastric notches. The atlanto-occipital joints should be below this line.=Basilar invagination is not the only condition in which the odontoid is unduly high: an abnormally short clivus and/or occipitalization of the atlas can give similar appearances.
NB: Both basilar invagination and platybasia are best assessed by mid-line sagittal MRI, when the effects on the neuraxis are also displayed.
III-Occipitalization of the Atlas:
The first cervical vertebra is fused to the skull base.
1% of the population.
- In its mildest degree, the distance between the 2 posterior arch of the atlas and occipital bone is reduced and does not change with flexion and extension.
- In ‘assimilation’ of the atlas, bony fusion is complete, and no separate components of the atlas can be identified.
- The normal relationship of atlas and axis is, however, preserved, so that the odontoid is abnormally high.
- The potential significance of this anomaly lies in its association with the Chiari malformation.
in conditions such as:
- Very wide sutures, without other signs of raised intracranial pressure.
- Wormian bones are prominent.
- It is usually evident that the patient has a generalized bone disorder.
- A condition in which the orbits seem widely separated.
- Usually associated with well developed ethmoid cells occupying the gap between the orbits.
- Present in:
1-Isolated congenital lesion (Grieg’s disease).
2- Osteogenesis imperfecta.
3- Cleidocranial dystosis.
4- Fibrous dysplasia.
6- Secondary to mucocele of ethmoid sinus (acquired).
*Apeurt’s syndrome = Syndactyly + oxycephally.
*Acrocephally = Summit skull (brachycephally) (same as tower skull).
*Crourzon’s disease = (hereditary craniofacial dysostosis) is a form of acrocephally + facial bone hypoplasia, hypertelorism, exophthalmos, parrot-beak nose, prognathism, MR & corepulmonale .
*Carpenter’s syndrome = acrocephalopolysyndactyly