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360
Chapter 11 Intracranial Cysts
A
C
E
B
D
Figure 11–9.
(B) Although some views raised the suspicion of agenesis of the corpus callosum, this parasagittal image (especially some radially oriented gyri) shows
the presence of a laterally displaced but normal-appearing corpus callosum ( arrow ) . (C) 3D coronal tomographic sequence of the cyst. (D) 3D sagittal
tomographic sequence of the cyst. (E) 3D axial tomographic sequence of the cyst. In addition to the above mentioned possible differential diagnosis
of a partial agenesis of the corpus callosum we also considered schizencephaly as an alternative diagnosis. A postnatal MRI confirmed the diagnosis of
arachnoid cyst parting the two hemispheres.
to favor fenestration over shunt insertion as the method
of choice for initial cyst decompression.
spective review presented the outcomes of 42 infants who
underwent craniotomy for fenestration of an arachnoid
cyst prior to the age of 2 years.
experience, they recommended that infants with arachnoid cyst and ventriculomegaly should have fenestration
initially. Shunt placement may be necessary later in most
cases. In infants who presented with nonspecific macrocephaly, initial fenestration was sufficient in 40%. These
Interhemispheric arachnoid cyst. (A) Two side-by-side coronal views of the cyst. Note the thin cyst wall ( arrow ) that depicts the diagnosis.
41
A recent retro-
did not require subsequent shunting procedure. Only
10% of the patients who presented with other symptoms,
such as seizures, headache, motor deficits, or develop-
40
Based on these authors’
mental delay, required subsequent shunting procedure
after fenestration.
The long-term prognosis of more than 60 children
with arachnoid cysts showed that 64% had a complete
recovery after treatment, 15% had a slight deficit, 13% had
severe postoperative deterioration, and 8% died.
46
The
outcome of these children was dependent on the location
Chapter 11 Intracranial Cysts
361
A
B
C
C
D
E
Figure 11–10. Aneurysm of the vein of Galen at 33 postmenstrual weeks. A–C. C-coded Doppler images of the lesion ( arrows ) . (A) The median plane.
(B) The midcoronal–1 plane. (C) In the median plane, note the wide (∼1.2 cm) structure above the cerebellum (C) with flow toward the posterior pole of
the brain. The Doppler evaluation showed a pulsating venous flow. (D) Grayscale image in the median plane. (E) Four-chamber view of the heart showing
relative cardiomegaly; heart-to-chest diameter ratio: 0.65 (normal 0.45–0.5) and a very small amount of pericardial effusion ( arrow ). There was no atrio-
ventricular valve regurgitation, but the heart had hyperdynamic motion consistent with a cerebral arteriovenous malformation. There was no dilation of
the vessels in the neck of the fetus. Three attempts at embolization were performed after the delivery, but the neonate died during the last such attempt.
362
Chapter 11 Intracranial Cysts
AB
C
Figure 11–11.
median plane. (C) 2D power Doppler median plane. (D) 2D power Doppler median plane of a normal vascular pattern for comparison.
Aneurysm of the vein of Galen at 22 postmenstrual weeks. (A) Two-dimensional (2D) grayscale median plane. (B) 2D color Doppler
of the cyst; of those children with temporal cysts, 93% had
full recovery or minimal deficit, and none died, versus 64%
of patients with cysts in other locations did well, and 16%
died.
INTRAVENTRICULAR CYST
Choroid plexus cysts (CPCs) are the most common type of
intraventricular cystic lesion.
D
0.18–3.6%) of all fetuses scanned.
47 – 54
CPCs are usually
not diagnosed before 17 to 18 postmenstrual weeks, and
in the majority of cases, do resolve by 26 postmenstrual
weeks.
Pathogenesis
The choroid plexus is responsible for the production of
CSF. CPCs are thought to result from filling of the neuroepithelial folds with CSF. At 6 to 7 postmenstrual weeks, the
Synonyms
None
choroid plexus starts developing in the roof of the fourth
ventricle, next in the lateral ventricle, and then in the third
ventricle, as fingerlike projections of neuroepithelium into
the ventricles, creating choroidal villi. The choroid plexus
Definition
This is a fluid-filled cystic space that accumulates within
the choroid plexus.
Incidence
CPC is a common finding during the second trimester
of pregnancy, with a reported incidence of 0.95% (range
grows rapidly and by 9 postmenstrual weeks fills 75% of
the cavity of the lateral ventricle. Portions of the epithelium are pinched off and become either tubules or cysts
lined with neuroepithelium within the choroidal matrix.
By the 20th week, the choroid plexus has achieved its adult
appearance.
48 – 50
The choroid plexus cyst may be unilateral
or bilateral and vary in size, although they tend to be < 10
mm in diameter. Resolution of the cysts is frequently seen
regardless of the fetal karyotype.
Chapter 11 Intracranial Cysts
363
E
Figure 11–11. (continued) (E) Serial coronal 2D grayscale images of the pathology.
Etiology
The etiology of CPC is not well understood, as most
fetuses who have CPC do not have any other structural or
chromosomal malformation. However, the presence of this
finding, especially in conjunction with additional sonographic abnormalities, has been associated with trisomy
18; in fact, as many as 50% of the fetuses with trisomy 18
may have a choroid plexus cyst. In addition, choroid plexus
cysts have been reported in association with cri du chat
(5p-) syndrome and mosaic trisomy 9.
ciation between CPC and trisomy 21 has been ruled out by
almost all well-designed studies.
51 – 55
A possible asso-
56
Associated Anomalies
Most CPCs are isolated findings in normal fetuses.
Nevertheless, the detection of CPC mandates a meticulous
targeted scan to look for other malformations, in particular those that are seen in fetuses with trisomy 18.
anomalies include congenital heart malformations (more
commonly ventricular septal defect, polyvalvular dysplasia,
bicuspid aortic or pulmonary valves, and coarctation of the
aorta), brain anomalies (eg, holoprosencephaly, meningomyelocele, Arnold-Chiari malformation, abnormal
gyration, and hydrocephaly), facial anomalies (eg, lowset or malformed ears, micrognathia, and cleft palate),
renal abnormalities (eg, horseshoe kidney, hydroureter,
Pathology
Arachnoid cysts are generated by splitting of the arachnoid
membrane which is then reinforced by a thick layer of collagen to result in a cyst. They are lined with a layer of meringothelial cells. They may be unilocular or multilocular.
and hydronephrosis), skeletal anomalies (eg, overlapping
fingers, rockerbottom feet, and clubfoot), nuchal thickening, cystic hygroma, and single umbilical artery.
investigators believe that cyst size or laterality is not an
indication of an associated chromosomal anomaly and that
all CPCs warrant similar investigation.
57
54 , 58 , 59
These
Most
364
Chapter 11 Intracranial Cysts
F
Figure 11–11. (continued) (F) Serial coronal 2D power Doppler images of the pathology.
Risk of Recurrence
Most of these lesions resolve spontaneously and are not
associated with an abnormal fetal condition and thus
do not recur in subsequent pregnancies. Even in cases
in which CPCs are associated with trisomy 18, they are
mostly sporadic, and the risk of recurrence in subsequent
gestations is not thought to be significantly higher. Trisomy
18 is generally a nonrecurrent chromosomal anomaly, and
unlike trisomy 21, chromosome 18 is not acrosomal and
thus is not frequently involved in unbalanced translocations. However, rare familial translocations have a higher
recurrence risk, depending on the specific translocation.
in Figures 11–14 , 11–15 , and 11–16 . Although most CPCs
are isolated findings in normal fetuses, the detection of a
CPC mandates a meticulous targeted scan to look for other
malformations, as we previously described.
Differential Diagnosis
The differential diagnosis of CPC includes: epidermoid
cysts, colloid cysts, focal porencephaly and arachnoid
cysts. Another entity that may results in an intraventricular cyst is choroid plexus hemorrhage, which has a
hyperechogenic appearance in the first 72 hours, after
which the cyst becomes less echogenic as the blood clot
dissolves.
Sonographic Diagnosis
The sonographic appearance of a choroid plexus cyst is that
of a sonolucent structure within the hyperechogenic choroid
plexus. The CPCs are usually small, measuring <10 mm in
size, with a range of 3 to 20 mm. Their borders are well delineated and are located within the choroid plexus; they may
be unilateral or bilateral and contain debris or other small
cystlike structures.
50 , 52 , 60 – 64
Several examples are presented
cystic structure in a choroid plexus.
Implications for Targeted Examination
The detection of a choroid plexus cyst is an indication
to perform a targeted detailed sonographic evaluation
looking for other intracranial and extracranial anomalies, with particular attention to the systems involved in
cases of trisomy 18. Follow-up until the CPC disappears
1
Choroid plexus papilloma can also present as a
Chapter 11 Intracranial Cysts
365
G
Figure 11–11. (continued) (G) 3D grayscale multiplanar views of the pathology. The arrows point to the dilated vein.
may be indicated because of the rare possibility of an
obstructive hydrocephaly.
65
Prognosis
These cysts are usually asymptomatic and benign. They
commonly resolve by the midtrimester (26 weeks) and
Figure 11–12. 3D orthogonal display of a posterior fossa arachnoid
cyst in a fetus at 22 postmenstrual weeks. Note the misleading axial
section ( lower image ) with the widely displaced cerebellar hemispheres.
However, the median plane ( upper right image ) clearly demonstrates the
intact but anteriorly displaced vermis and the pressure on the medulla.
have been associated with both a normal and an abnormal
fetal karyotype.
bilaterality, and size are not thought to be associated with
an increased risk of chromosomal abnormality. Failure to
resolve after 25 to 26 weeks’ gestation does not alter the
prognosis, but these patients should be followed because
of the extremely rare possibility of ventricular obstruction
with the development of ventriculomegaly due to obstruction of the foramen of Monro.
Obstetric Management
Management of pregnancies with a choroid plexus cyst
has been a subject of great controversy, with several
studies with conflicting data regarding the association
of isolated CPC and trisomy 18. Subsequently, a wide
61 , 62 , 64 , 66 – 68
Similarly, the number of cysts,
366
Chapter 11 Intracranial Cysts
C
A
CD
Figure 11–13. A large posterior fossa (mainly to the left) arachnoid cyst of a fetus at 28 postmenstrual weeks. (A) Occipital–1 section showing the
cystic structure ( white arrow ). (B) Median section showing the normal-appearing midline structures, as well as the sonolucent structure ( white arrow )
displacing the cerebellum (C). The lesion was followed up until delivery occurred. C, D. MRI of the neonate. (C) Coronal image of the posterior fossa
showing what appeared to be a cerebellar arachnoid cyst displacing both lobes of the cerebellum. (D) Median image of the brain clearly showing the
cystic structure in the posterior fossa with displacement of the cerebellum and midbrain. The diagnosis of arachnoid cyst was arrived at because there
was minimal deformity of the vermis, which is the mark of Dandy-Walker malformation. The fourth ventricle is of normal size but slightly pushed by the
increasing cerebrospinal fluid (CSF) pressure. The lateral and third ventricles were of appropriate size. There was no evidence of hemorrhage.
B
range of clinical practices have emerged regarding the
need to check the fetal karyotype or inform patients of
such a finding when it is indeed isolated. When a fetus
with CPC has other malformations or a soft sonographic
marker, there is no doubt that genetic counseling is
indicated, and genetic testing should be offered. The
disagreement pertains to the need for genetic counseling
and fetal karyotyping in cases in which the CPC is an isolated finding. Some authors recommend that all patients
should be offered genetic testing because the experience,
equipment, and/or ability of all sonographers or sonologists may not be equal, and some less experienced operators may miss an associated malformation.
47 , 50 , 58 , 64 , 67 , 69 – 72
Other authors believe that only in the presence of an
associated congenital anomaly is genetic testing justified and that invasive testing is not indicated for isolated
CPC.
54 , 59 , 61 , 73
Kupferminc et al
58
reported the risk of chromosomal abnormality in cases of isolated choroid plexus
cyst to be 1:25. In their series of 98 cases of isolated CPC,
4 abnormal karyotypes were found among 75 women
16w
Chapter 11 Intracranial Cysts
367
A
B
C
Figure 11–14. Routine structural evaluation at 16 postmenstrual weeks revealed a unilateral choroid plexus cyst measuring 0.4 × 0.36 × 0.36 cm.
The white arrow points to the small choroid plexus cyst. (A) “Horizontal” section. (B) Midcoronal–3 section. (C) Occipital–1 section.
RT
LT
AH
OH
ABC
19w
Figure 11–15. Three different views of bilateral and septated choroid plexus cysts at 19 postmenstrual weeks. (A) “Horizontal” section.
(B) Midcoronal–1 section. (C) Oblique–1 section showing the normal anterior horn (AH) and posterior horn (OH). The neonate was normal.
368
Figure 11–16. Three views of bilateral choroid plexus cysts at 19 postmenstrual weeks. (A) “Horizontal” section, with the largest cyst measuring
1.2 × 2.6 cm. (B) Occipital–2 section. (C) Occipital–1 section depicting both posterior horns and the cerebellum with the normal vermis ( white arrow ).
At 24 postmenstrual weeks, the choroid plexus on the left side was no longer apparent, and all the lateral ventricle measurements were within the normal
limits. At 29 postmenstrual weeks, the left choroid plexus cyst disappeared. A repeated scan at 33 postmenstrual weeks showed normal brain anatomy.
The neonate was normal.
Chapter 11 Intracranial Cysts
ABC
who elected to have amniocentesis. Of the four abnormal
karyotypes, three were Down syndrome (trisomy 21) and
one trisomy 18.
58
Gross et al
54
subsequently reported on
the risk of trisomy 18 in cases of isolated choroid plexus
cyst. Using a meta-analysis and their own cases, they were
able to calculate a risk of trisomy 18 in cases of isolated
choroid plexus to be 1:374.
54
It is our practice to inform the patient of this finding
and to incorporate it into our counseling, which is based
on the patient’s a priori risk of fetal trisomy. We do not
recommend invasive testing for fetal karyotyping in cases
of isolated CPC in which other fetal anomalies or soft
sonographic markers were excluded and first and/or second trimester screening tests were normal.
INTRAPARENCHYMAL CYST
Intraparenchymal cystic structures may result from different insults, such as hemorrhage, ischemia, infection, and
tumor. The prognosis depends primarily on the etiology,
location, and size of the lesion and the presence or absence
of associated anomalies.
Periventricular Pseudocyst
Definition
A small intraparenchymal periventricular cystic lesion that
is not lined by epithelium and lacks a real cyst wall (i.e.
periventricular pseudocyst).
Synonyms
Germinolysis, periventricular cyst.
Incidence
This finding is uncommon during the ultrasonographic
evaluation of the fetus; however, the incidence is ∼1%
among newborns in the general population and as high as
3% in newborns admitted to the intensive care unit.
74 – 76
Pathogenesis
The pathogenesis of periventricular pseudocysts is unclear,
as well as the exact timing in which it occurs. The latter
is probably related to the specific etiology or precipitating exposure. Pathologic examination of such lesions
detected that the pseudocysts are lined with macrophages,
suggesting the process of prior malacia, whereas others
show positive staining for iron pigment, suggesting prior
hemorrhage.
Etiology
Periventricular pseudocysts are thought to be the result of
antenatal cystic matrix regression or germinolysis and are
probably the outcome of hemorrhage or microinfarction
of the germinal matrix. The most common etiology associated with these findings is infection with cytomegalovirus
(CMV). Other, less common etiologies are other TORCH
infections (toxoplasmosis, other infections, rubella, herpes simplex virus), cardiac malformations, chromosomal
microdeletion (4p-), and metabolic or mitochondrial dis-
1
orders.
Associated Anomalies
Other anomalies or sonographic findings that can be
detected in association with periventricular pseudocysts
Chapter 11 Intracranial Cysts
AB
CD
Figure 11–17. Periventricular pseudocysts ( arrows in A–C ) in a fetus with suspected skeletal dysplasia ( D ) at 24 weeks’ gestation. Note that the cysts
are difficult to visualize in the transabdominal axial image ( A ).
369
are those characteristic for CMV infection. These findings
include intraparenchymal calcifications, ventriculomegaly,
large cisterna magna, intraventricular adhesions, periventricular cysts, abnormal sulcation, hypoplastic corpus
callosum, and liver calcifications.
77
Risk of Recurrence
Periventricular pseudocysts
do not recur in future pregnancies. Rare exceptions are
cases associated with hereditary metabolic or mitochondrial disorders.
78 – 85
are generally sporadic and
Sonographic Diagnosis
The prenatal sonographic diagnosis of periventricular
pseudocysts has been described by Malinger et al.
on their experience, these lesions could be suspected and
at times detected using the traditional abdominal axial
scanning planes ( Figure 11–17 ). However, transvaginal,
high-frequency scan of the fetal brain in the coronal and
sagittal planes provided additional information and helped
the authors to distinguish these lesions from periventricular leukomalacia ( Figure 11–18 ).
Periventricular pseudocysts are usually located in the
germinal matrix, in the caudothalamic groove, caudate
nucleus, or lateral aspect of the frontal horns of the lateral
ventricles
tricles.
76
below the level of the roof of the lateral ven-
77
The cysts may be unilateral or bilateral, as well
as unilocular or multilocular. Our experience shows that
large cysts, even when isolated, may carry a poorer prognosis than smaller ones.
79
The role of MRI in the diagnosis of periventricular
pseudocyst is unclear. In one series describing five cases
of periventricular pseudocysts that were confirmed by
high-resolution transvaginal neurosonography by an experienced examiner, MRI did not diagnose the pseudocysts
78
Based
in two cases.
78
The authors hypothesized that this was due
to the small size of the pseudocyst or the thin wall and its
proximity to the ventricle. The benefit of doing MRI in
such cases is its ability to better depict brain migrational
anomalies that may coexist. Therefore, the authors concluded that an MRI should be performed in every case of
periventricular pseudocyst in order to rule out additional
pathologies and provide further reassurance.
78
Differential Diagnosis:
1. The complete differential diagnosis is displayed in
Table 11–1; however, the most difficult sonographic
distinction is between periventricular pseudocyst and
periventricular leukomalacia, which carry a significantly worse prognosis ( Figure 11–18 ). Periventricular
LV
Figure 11–18. Periventricular leukomalacia ( arrows ) in a fetus at
31 weeks of gestation referred for evaluation because of mild asymmetric
ventriculomegaly. The cysts are placed on the roof of the lateral ventricle
instead of in the germinal matrix or caudate nuclei, as seen in patients
with periventricular pseudocysts.