1) Chiari malformation(Fig.6)
Hans Chiari as Austrian pathilogist in 1891 had divided Chiari malformation into four categories:
Type I : more than 5mm of descent of only the cerebellar tonsil
Type II : descent of the cerebellar tonsil,
vermis,
the fourth ventricle and medulla oblongata
At present,
type I and type II are classified by the absence or presence of myelomeningocele
Type III : accompanied with the occipital meningocele
Type IV : cerebellar hypoplasia
At present,
this is not included in the Chiari malformation
Hydrocephalus and syringomyelia is accompanied with 10% : 50-85% in type I and 90% : 20% in type II,
respectively.
Chiari type I and type II are embryologically distinct disorders.
Chiari type I is defined as the abnormal formation of the paraxial mesoderm,
leading to hypoplasia of the occipital bone and the shallow posterior fossa.
Chiari type II is defined as defective development of primitive ventricle (especially near the fourth ventricle) due to discharge of CSF to the amniotic cavity by myelomeningocele,
leading to the shallow posterior fossa.
2) Craniosynostosis(Fig7-9)
Craniosynostosis is accompanied with deformity of the skull by the premature fusion of the suture.
This incidence rate is one in 2100-2500 people.
Craniosynostosis is mostly correlated with abnormality of TWIST1 gene and fibroblast growth factor receptor(FGFR) gene,
such as Apert syndrome,
Crouzon disease(Fig.7),
Pfeiffer syndrome(Fig.8-9),
Muenke syndrome,
Beare-Stevenson syndrome and Jackson-Weiss syndrome.
Muenke syndrome and Crouzon disease accompanied by acanthosis nigricans are caused by mutation of the FGFR3,
the other diseases are mostly caused by mutation of the FGFR2.
In the report of T.
de jong et al,
it has been considered that there are no differences between the brain volume in healthy group and in patients with craniosynostosis.
Cranioencephalic disproportion makes prone to herniation.
Fusion of lambdoid suture is most correlated with the shallow posterior fossa.
3) Increased volume of intracranial contents(Fig.10)
In many cases,
CTH is caused by posterior fossa tumors and cerebellar hemorrhage,
and often accompanied with hydrocephalus.
Not only infratentorial lesions but also supratentorial lesions can cause CTH.
3)' Acromegaly(Fig.11)
CTH is observed in 15% of patients with acromegaly,
it shows more than 5mm of descent of the tonsil in 4.7% in the report of Renzo et al.
Some symptoms such as headache and visual disturbance occur.
These patients with symptoms are at significantly higher rate than in the healthy group.
Those who are lower age,
short disease duration,
no history of hypertension and no treatment with a growth hormone(GH) receptor antagonist have a tendency to have symptoms.
Two cases were accompanied with syringomyelia.
Sievers et al have suggested that GH/IGF-1(insulin-like growth factor) have had a trophic effect of neurogenesis and oligodendrogenesis,
therefore that excess secretion of the GH/IGF-1 have caused diffuse increase of extracellular fluid and cell volume.
Overgrowth of bone of the patients with acromegaly is extrovert,
so intracranial volume does not correlate to enlarging head circumference.
CTH may be improved by treatment for acromegaly,
and by brain atrophy when it comes to aging.
4) Abnormal intracranial pressure(Fig.12-13)
Increased intracranial pressure with any causes leads to downward displacement of the intracranial contents to the spinal canal with the relatively lower intraspinal pressure.
Intracranial hypotension/CSF hypovolemia syndrome is a condition of the cerebrospinal fluid leakage occurring with some triggers such as minor trauma and spinal surgery.
CSF leaks causes the downward slope of the pressure above and below the foramen magnum,
and induces the descent of the cerebellar tonsils.
Thick dural enhancement,
bilateral subdural hematomas,
enlarged pituitary gland are sometimes found.
Repetitive lumbar puncture and lumboperitoneal shunt also cause CTH in same mechanism.
Jorge A.
Lazoreff et al.
have reported CTH induced by long-term ventriculoperitoneal shunt,
but have suggested that the patient had been potentially accompanied with hypoplasia of the posterior fossa.
3)+4) Macrocephaly capillary malfomation (Macrocephaly-cutis marmorata telangiectatica congenita)(Fig.14)
Macrocephaly-capillary malformation is a multiple congenital anomaly syndrome in children with macrocephaly,
overgrowth,
skin abnormalities with diffuse marbled skin,
philtrum and upper lip vascular anomaly,
syndactyly and hyperlaxity of the joint.
It is associated with obstructive/non-obstructive hydrocephalus,
and 8-69% of the patients with it is accompanied with CTH.
Hydrocephalus and increased volume of the cerebellum due to edema with the failure of the venous circulation,
are considered to cause CTH.