Keywords
arachnoid cyst - neuroendoscopy - performance IQ - route-finding disorientation -
velum interpositum - visual–spatial construction apraxia
Introduction
The velum interpositum (VI), contrary to its appearance of being located inside the
brain, is interposed between the bilateral hemispheres and the diencephalon. The posterior
choroidal arteries and choroid plexus enter from the galenic cistern into the VI,
run anteriorly, and exit at the foramen of Monroe. Internal cerebral veins (ICVs)
enter the VI at the foramen of Monroe, run posteriorly, exit to the galenic cistern,
and join the vein of Galen.
Dilatation of the VI space is normally documented during the fetal period and has
been defined as cavum veli interpositi (CVI). The CVI usually decreases in size after
birth[1]; however, rare cases with persistent or enlarged CVI require treatment. Two theories
of the anatomical definition of CVI exist. Kier[2] indicated that the CVI lies within the double-layered tela choroidea, not superior
to it; therefore, ICVs are within the CVI, not inferior to it. On the other hand,
Chen et al.[3] indicated that the CVI is a true cistern above the third ventricle, and ICVs form
parts of the inferolateral boundaries of the CVI, but are not within it. The debate
ended with the classification of two forms of enlarged VI; namely, Kier's CVI relating
to enlarged VI, and Chen's CVI relating to an arachnoid cyst in the VI.[4] The location of ICVs is the key condition driving differentiation. An enlargement
of the CVI or arachnoid cyst is suggested to be caused by head trauma followed by
arachnoid adhesion, creating a ball valve mechanism between the VI and the galenic
cistern.[5]
CVI and an arachnoid cyst in VI seldom present with increased intracranial pressure
(ICP),[6] instead, developmental delay,[7]
[8] psychiatric symptoms,[8]
[9] and memory disturbance[4] have been reported. In contrast, cavum septum pellucidum and cavum vergae, which
commonly present with headache, are not associated with behavioral disturbance and
tend to be less frequent.[10]
[11]
Herein, we report an older patient with an arachnoid cyst in VI, presenting with selected
symptoms among the cognitive dysfunctions, namely, a normal verbal intelligence quotient
(IQ) and decreased performance IQ (PIQ). Her symptoms were reversed by neuroendoscopic
fenestration. The mechanism of the symptoms caused by the arachnoid cyst location
and morphology is discussed, with consideration of functional neuroanatomy.
Case Presentation
A 60-year-old woman, a right-handed homemaker and a high school graduate, who had
no history of illness, underwent head magnetic resonance imaging (MRI) as part of
a medical checkup, and dilatation of the VI was incidentally identified ([Fig. 1A]). She had no neurological symptoms at the time. Eight years later, she suffered
from unstable gait, difficulty with housekeeping procedures, and getting lost when
going out. She had no sign of increased ICP. However, MRI revealed an enlarged VI
of 67 mm in longitudinal length, 77 mm in width, and 59 mm in vertical length. The
corpus callosum and ICVs shifted upward and downward, respectively. These findings
suggested a diagnosis of an arachnoid cyst in the VI rather than CVI. Her lateral
ventricles were compressed laterally and had collapsed ([Fig. 1B, C]).
Fig. 1 Serial head MRI before surgery. (A) Head MRI taken 8 years before admission. A cyst
in the velum interpositum is revealed. (B, C) MRI taken before surgery. The cyst expands,
and the lateral ventricle decreases in size. Internal cerebral veins (ICVs) are located
at the bottom of the cyst. No tightness of sulci is observed. MRI, magnetic resonance
imaging.
Preoperative cognitive tests were conducted, and she scored 28/30 points on the Mini-Mental
State Examination (MMSE), 16/18 points on the Frontal Assessment Battery (FAB), and
86 on the full-scale IQ of the Wechsler Adult Intelligence Scale version III (WAIS-III;
[Table 1]). Her PIQ was 68, significantly lower than her verbal IQ of 103. Among the subtests,
significantly low scores were marked in picture arrangement, picture completion, and
symbol search with 4, 1, and 5 points, respectively, and a normal score: 10 points.
Her copies of the interlocking pentagons and cube designs were transformed, rotated,
and distorted ([Fig. 2]). She was able to use everyday tools, to gesture movements correctly, and she required
no assistance with changing clothes, indicating no ideational apraxia, ideomotor apraxia,
or dressing apraxia. Her gait was mildly unstable; however, it was fast enough at
11.2 seconds in the 3-meter Timed Up and Go test (3mTUG). Her neurological signs and
symptoms were summarized as route-finding disorientation without landmark agnosia,
and visual–spatial construction apraxia without visual–spatial agnosia.
Table 1
Scores of pre- and postoperative cognitive tests
|
|
Age-matched average
|
Preop. score
|
Postop. score
|
|
WAIS-III
|
|
Index scores
|
Full-scale IQ
|
100
|
86
|
100
|
|
Verbal IQ
|
100
|
103
|
104
|
|
Performance IQ
|
100
|
68
|
94
|
|
Verbal comprehension
|
100
|
104
|
107
|
|
Perceptual organization
|
100
|
72
|
95
|
|
Working memory
|
100
|
107
|
103
|
|
Processing speed
|
100
|
78
|
94
|
|
Verbal subtest
|
Vocabulary
|
10
|
10
|
10
|
|
Similarities
|
10
|
9
|
11
|
|
Information
|
10
|
13
|
13
|
|
Comprehension
|
10
|
8
|
10
|
|
Digit span
|
10
|
11
|
11
|
|
Letter-number sequencing
|
10
|
12
|
9
|
|
Arithmetic
|
10
|
11
|
12
|
|
Performance subtest
|
Picture arrangement
|
10
|
4
|
7
|
|
Picture completion
|
10
|
1
|
7
|
|
Block design
|
10
|
7
|
9
|
|
Matrix reasoning
|
10
|
9
|
12
|
|
Symbol search
|
10
|
5
|
11
|
|
Digit symbol
|
10
|
7
|
7
|
|
MMSE
|
|
28[a]
|
28
|
29
|
|
FAB
|
|
17.1[a]
|
16
|
16
|
Abbreviations: FAB, Frontal Assessment Battery; IQ, intelligence quotient; MMSE, Mini-Mental
State Examination; WAIS-III, Wechsler Adult Intelligence Scale Version III.
a Indicate the scores of the age and education-matched average.[13]
[14]
Fig. 2 Preoperative drawing test of interlocking pentagons and cube. (A) The left equilateral
pentagon transforms to a house base shape, and the right one rotates. (B) The cube
distorts.
Surgical Findings
Neuroendoscopic fenestration of the cyst was performed. A right lateral ventriculostomy
was done through the frontal burr hole. The cerebrospinal fluid (CSF) opening pressure
was 10 cm H2O. Under observation with Videoscope® (Olympus, Tokyo, Japan), the septum pellucidum
and cyst wall were fenestrated together ([Fig. 3A]). The ICVs were visualized at the bottom of the cyst ([Fig. 3B]). Through the location of the ICVs, the presence of an arachnoid cyst in the VI
was confirmed. The body of the right lateral ventricle was identified from the location
of the choroid plexus seen through the cyst wall, and a second fenestration was created
there. By carefully avoiding the damage on the left crus of the fornix, we observed
the pulsation of the cyst wall on the galenic cistern; however, no slit valve was
found.
Fig. 3 Endoscopic views in the lateral ventricle and the cyst. (A) Right anterior horn of
the lateral ventricle. The septum pellucidum is fenestrated together with the cyst
wall. The choroid plexus is seen on the right side. (B) Panorama picture reconstructed
from the endoscopic photos. ICVs seen on the right side entering the vein of Galen
are confirmed to be located at the bottom of the cyst. The choroid plexus of the left
lateral ventricle is transparently seen through the cyst, and the ventricle wall is
located on the left side. The crossing portion of the left ICV and the choroid plexus
is the left foramen of Monroe. The upper side of the picture is the frontal side of
the patient. ICV, internal cerebral vein.
Postoperative Course
Three months postoperatively, she obtained a score of 29/30 points on the MMSE; 16/18
points on the FAB; and 100 for her full-scale IQ on the WAIS-III ([Table 1]). Her PIQ had improved remarkably from 68 to 94. Among the subtests, scores on picture
arrangement, picture completion, and symbol search increased from 4, 1, and 5 to 7,
7, and 11, respectively. She was able to copy the pentagons and cube designs correctly
([Fig. 4]). Her gait was stable with 9.9 seconds in 3mTUG. MRI revealed that the cyst had
decreased in size to 50 mm in longitudinal length, 60 mm in width, and 37 mm in vertical
length ([Fig. 5]). Although we had fenestrated the cyst wall bilaterally, only the right-sided stoma
was patent.
Fig. 4 Postoperative drawing test of interlocking pentagons and a cube. (A) The transformation
and rotation of the pentagons are corrected. (B) The distortion of the cube is corrected.
Fig. 5 Postoperative MRI. (A, B) Head MRI taken 3 months after surgery. The cyst decreases,
and the lateral ventricle increases in size. MRI, magnetic resonance imaging.
Discussion
A patient with an arachnoid cyst in VI was reported. The recovery with a decrease
in cyst size indicated the symptoms were caused by compression and extension of the
nerve fiber tracts in the white matter.[12] We herein discuss the mechanisms by which the frontal lobe dysfunction was mild
and the parietal lobe functions were partly impaired.
Frontal Lobe Functions
The patient presented with a mildly disturbed gait, small reductions in MMSE[13] and FAB,[14] and no disturbance in her verbal IQ, working memory, and urination control. As the
VI is shaped like a cone, the apex, pointing to the foramen of Monroe, is thin compared
with the wide bottom located between the crus of the fornix. Even when the arachnoid
cyst in VI expanded, compression to the frontal lobes was still milder than that to
the parietal lobes ([Fig. 6A]). Moreover, slit-like lateral ventricles due to compensated elimination of CSF in
response to the expansion of the cyst avoided the frontal lobe compression. Therefore,
emotion, motivation, urination control, and higher cerebral function controlled by
the frontal lobes were within normal limits. The prefrontal cortico–ponto–cerebellar
pathway for gait stabilization was not disturbed either; however, compression to the
pyramidal tracts for legs located near the lateral ventricles in the posterior frontal
lobes seemed responsible for her mildly disturbed gait.
Fig. 6 Schematic explanation of the mechanism of the topographically different influence
from the cyst. (A) Axial view. The cone-shaped cyst (black triangle) compresses severely
to the parietal lobes (arrows) and mildly to the frontal lobes. (B) Coronal view.
A short nerve fiber located superficially (left side) is not damaged. A long fiber
tract connecting the distant gyri (right side) and passing close to the cyst (black
solid) is prone to compression. The grayscale of the brain indicates the parenchymal
pressure gradient.
Parietal Lobe Functions
She exhibited low PIQ, especially in visual–spatial construction test, including the
picture arrangement test, picture completion test, symbol search test, copies of the
interlocking pentagons, and cube designs, but did not show other parietal dysfunction
such as ideational apraxia, ideomotor apraxia, or dressing apraxia. The pressure gradient
in the brain mantle of the parietal lobes ([Fig. 6B]) explains a suspected mechanism of the selective dysfunction in the patient. As
the long fiber tracts connecting remote gyri run in the deep white matter, the cyst
severely compressed and stretched the nerves. On the other hand, short fibers connecting
within a gyrus or adjacent gyri run in the superficial portion of the brain, and thus,
escape from compression. The visual–spatial construction function requires the bilateral
parietal cortices and the corpus callosum connecting them.[15]
[16]
[17]
[18] Seydell-Greenwald et al.[17] reported the bilateral parietal activations in functional MRI under the visual spatial
task. Compression of the corpus callosum caused her construction apraxia. Although
she presented visual–spatial apraxia, she did not present visual–spatial agnosia or
dressing apraxia. Those functions require only the right parietal lobe. She also retained
the functions controlled by a single gyrus in the left parietal lobe, such as ideational
function and ideomotor function.
Topographical Disorientation
The patient suffered from determining the direction she should choose in known places
where she recognized the streets and landmarks. Among topographical disorientation,
landmark agnosia is a type of visual memory disturbance caused by a lesion in the
occipitotemporal area, which the cyst of the patient did not affect. Her symptom is
known as route-finding disorientation or heading disorientation. This function is
controlled by the posterior cingulate cortex,[19]
[20] which was close to the cyst in the patient.
Conclusion
A patient with an arachnoid cyst in VI presenting with constructional apraxia and
route-finding disorientation was reported. Disturbance in the biparietal connections
and the posterior cingulate gyrus caused the symptoms, respectively. The characteristic
cone-shaped cyst affected the deep parietal region more severely than the frontal
lobes or superficial parietal lobes.
