:ActaNcurochirurgica
Acta Neurochir (Wien) (1990) 104:147-150
© by Springer-Verlag 1990
Dynamic Aspects of Expanding Cava septi pellucidi et Vergae K. Wester 1, P.-H. Pedersen l, J. L. Larsen 2, and P. E. Waaler 3 1Department of Neurosurgery, 2Department of Radiology, Neuroradiology Section, 3Department of Pediatrics, University of Bergen, School of Medicine (Haukeland Hospital), Bergen, Norway
Summary
Methods
Two paediatric patients with expanding cysts of the cava Vergae et septi pellucidi are presented. In the first patient, consecutive CT scans showed a growing cavum thought to be responsible for his dramatic increase in head circumference. In the other patient, the expanding cavum was discovered because a routine skull X-ray after minor head trauma revealed marked impressiones digitatae. Both patients were successfully treated with stereotactically placed internal shunts from the cysts via the lateral ventricle to the subarachnoid space. During this procedure, contrast medium was instilled, and the cysts were visualized on postoperative CT scans. Some dynamic aspects of such expanding cava are discussed.
We chose a surgical approach that was slightly modified from the one reported by Donauer et al. 5. Using the Leksell stereotactic system, the cava were punctured and diluted contrast medium, Iohexol (Omnipaque ®), was instilled to obtain CT-visualization of the cysts. In one patient (Case 1), a CT scan was performed at this stage of the procedure (Fig, 1). Then, an angled Holter ventricular catheter
Keywords: Cavum Vergae; cavum septi pellucidi; cerebral cysts; cerebral ventricles; hydrocephalus; shunt; stereotactie techniques.
Introduction T h e c a v u m V e r g a e a n d the c a v u m septi pellucidi, c o n f l u e n t fluid c o m p a r t m e n t s i n t e r p o s e d between the third ventricle a n d the c o r p u s callosum, are r e g u l a r findings in p r e m a t u r e n o r m a l b r a i n s a n d at birth, b u t b e c o m e g r a d u a l l y less frequent in c h i l d h o o d a n d adolescence 6, 8, 13 Persistent, a s y m p t o m a t i c c a v a are o c c a s i o n a l l y f o u n d on C T scans or at autopsies. M o r e rarely, enl a r g e d c a v a a s s u m i n g a cystic a p p e a r a n c e are found. Such cysts are believed to be o f s o m e clinical significance, as they m a y interfere with the i n t e r n a l d r a i n a g e o f C S F , thus causing h y d r o c e p h a l u s . H o w e v e r , the socalled colloid cysts o f the t h i r d ventricle m o r e often pose clinical p r o b l e m s , p o s s i b l y b e c a u s e they are m o r e p r o n e to give d r a m a t i c s y m p t o m s t h a n the c a v a cysts. T w o p a e d i a t r i c p a t i e n t s are r e p o r t e d , b o t h with clinical a n d r a d i o l o g i c a l signs o f increased i n t r a c r a n i a l pressure, a s s u m e d to be caused b y m a r k e d e n l a r g e m e n t o f the c a v a septi pellucidi et Vergae. O b s e r v a t i o n s m a d e in one o f the p a t i e n t s m a y shed s o m e light on the d y n a m i c aspects o f c a v a cyst d e v e l o p m e n t .
Fig. 1. Case 1. Intra-operative horizontal CT scans after stereotactic filling of the cyst with contrast medium. Note small amount of air in the anterior upper portion of the expanded cava septi pellucidi et Vergae
148
K. Wester et al. : Dynamic Aspects of Expanding Cave septi pellucidi et Vergae
Head circumference (cm)
OP. 60.
55,
50
:y;:;
45-
.. .-
40-
Fig. 4. Case 1. Horizontal CT scans 4 days (left) and 3 months after stereotactic insertion of an internal (cysto-ventriculo-subarachnoidal) shunt
35-
I
2
~
4 ; Months
~(oi'2 AGE
i //
2~
i
~ Years
Fig. 2. Case 1. Graph showing rapid increase in head circumference, and stabilization after the internal shunt procedure (arrow). The other lines represent the 2, 5, 50, and 97.5 percentiles in a Norwegian population of boys 7
was permanently placed into the cyst via the right lateral ventricle by stereotactic techniques. The length of the catheter was selected to match the distance from the burr hole to the postero-inferior border of the cavum Vergae, as measured from the CT scans. Additional side holes were cut in those parts of the catheter expected to be located in the lateral ventricle and the subarachnoid space, thus making the catheter a cysto-ventriculo-subarachnoid shunt. When the catheter reached the center of the cyst, the stylet was withdrawn, and the tip of the flexible catheter was introduced further into the posterior part. The extracranial part of the catheter was then ligated and secured to the periosteum by non-absorbable sutures. The other patient (Case 2), was subjected to a similar procedure, with the exception that the permanent catheter was implanted immediately after the injection of contrast medium into the cyst. The CT scanning was thus performed postoperatively.
Fig. 5. Case2. Preoperative coronal MR scan showing a cystic expansion of the cavum septi pellucidi
Case Descriptions and Results Case 1
This two and a half year old boy had a rapidly increasing head circumference from the age of 4 months (Fig. 2). As the patient showed no clinical signs of raised intracranial pressure and there
Fig. 3. Case l. Horizontal CT scans from nearly identical levels showing the development of an apparently non-expanding enlargement of the cava septi pellucidi et Vergae into an expansive cyst. Left: 10 months old. Middle: 13 months old. Right: 2 years, 1 month old. The cyst showed no further increase at the time of operation 3 months later
K. Wester et al. : Dynamic Aspec~.s of Expanding Cava septi pellucidi et Vergae
Fig. 6. Case2. Postoperative CT scans. Left: The immediate postoperative status. Note contrast medium in the collapsed cavum Vergae portion of the cyst, the catheter leaving the cyst, and air in the anterior portion. Right: 3 months postoperatively
was a family history of large heads, no other measures were undertaken for the following months apart from frequent check-ups, including CT scans. At the age of 9 months, the deviation of the head circumference had reached 1.1 cm above the 97.5 percentile, climbing to nearly 4cm at the age of 21/a years. Simultaneously, CT scans showed a continuously increasing size of the combined cava septi pellucidi et Vergae. The cava were already present in the first scans (Fig. 3). The transverse diameter of the cavity had eventually increased from 6 to 26 mm during the time of observation. This corresponds to a large increase of the cava volume, as they gradually assumed the shape of a sphere. Clinically, the patient showed no other signs of raised intracranial pressure than the increasing head circumference, his psychomotor development being adequate for age. The only conceivable explanation of the patient's growing head was a mild hydrocephalus, induced by the ballooning cava. Therefore, the internal shunt procedure (see Methods) was performed at the age of 2 years and 5 months. As a consequence, the cava collapsed (Fig. 4), the head circumference stabilized and has now remained unchanged for more than 12 months (Fig. 2). The boy is completely healthy. Case 2 At the age of 8 years, the second patient (also a boy) was admitted after a minor head injury. A routine X-ray of the skull showed marked irnpressiones digitatae, and it was found that during the previous year he had noticed impaired vision in one eye and brief episodes of unsteady gait, most probably due to a mild ataxia. A CT scan, and subsequently an MRI scan were therefore performed, showing moderate hydrocephalus and a cyst in the region of the cava septi pellucidi et Vergae (Fig. 5). The transverse diameter of the cyst was 32 ram. After the implantation of the internal shunt, the cyst collapsed, the radiological signs of hydrocephalus became less pronounced (Fig. 6), and the patient no longer experienced the episodes of unsteady gait.
Discussion
The course of one of the patients (Case 1), demonstrates the dynamic aspect of cystic cava septi pellucidi et Vergae. Over a period of 19 months, consec-
149
utive CT scans clearly showed that the cyst size changed dramatically. From being in principle an embryological remnant of no pathological significance, the cave in this case gradually expanded. It is reasonable to assume that the progressively increasing head circumference could be causally related to the enlargment of the cava, since this increase ceased following the internal shunt procedure which induced the collapse of the cava. However, the fact that the head circumference began to increase before the cava became radiologically expanded is intriguing. If the patient's hydrocephalus had some other cause than the enlarging cava, it is difficult to explain why an internal (cysto-ventriculo-subarachnoid) shunt could bring this process to an end. Two possible sequential processes may have been causative, first hydrocephalus of unknown aetiology, leading to a gradual expansion of the pre-existing cava, for example by means of a one-way valve mechanism. Once enlarged, the cava in their turn may have contributed to the progression of the hydrocephalus by obstructing the drainage from the lateral ventricles. Whatever the pathogenesis, a similar process may have occurred in the other patient prior to admission. For obvious reasons, it was not possible to obtain radiological evidence for this assumption. Persistent cava septi pellucidi et Vergae ("5th and 6th ventricles of the brain") are not infrequently tbund at routine examinations of human brains 91 - 1,13,14.Most of these cysts are small, their incidence declines with increasing age 13, and they are generally of no pathological significance. More rarely, such cysts obviously expand, probably a causative factor in the inadequate CSF drainage in these patients a' 4, 5, 12, 15 Shaw and Alvord ~3 distinguished between: 1) incidental, asymptomatic cysts, and 2) symptomatic cysts with increased pressure within the cyst. The observations in one of our patients indicate that there may be transitions between the two groups, and that a previously non-expanding cavity may develop into an expanding one. If children with persistent cava septi pellucidi et Vergae were followed routinely with CT or MRI scans, the pathogenesis of such a transition could be clarified. In the relevant literature, the lack of references and the age of the few papers most frequently cited (see e.g. 6, 10) are striking features, in sharp contrast to regularly appearing, numerous reports on colloid cysts of the third ventricle. In the Cumulated Index Medicus 1981-1988 (volumes 22-29), "colloid cysts" are mentioned nearly ten times more often than "cava septi pellucidi et/aut Vergae" or equivalent terms (37 vs. 4).
150
K. Wester et al.: Dynamic Aspects of Expanding Cava septi pellucidi et Vergae
B o t h processes are l o c a t e d at a critical level for C S F d r a i n a g e , a n d s h o u l d thus have the p o t e n t i a l o f p r o ducing d r a m a t i c s y m p t o m s if c o m p r o m i s i n g the C S F flow. T h e o b s e r v e d scarceness o f r e p o r t s on c a v a cysts in the l i t e r a t u r e m a y c a r r y s o m e i m p o r t a n c e . It m a y reflect t h a t s y m p t o m a t i c c a v a cysts in fact a p p e a r infrequently, b u t it m a y also reflect t h a t p o s s i b l y occurring s y m p t o m s f r o m these cysts are t o o v a g u e to be clinically recognized, in c o n t r a s t to w h a t is c o m m o n with colloid cysts. T h e p r e s e n t two cases illustrate this. T h e c o m b i n a t i o n o f relatively m i l d s y m p t o m s in o u r p a t i e n t s a n d the c o n s i d e r a b l e size o f their cysts is striking. I f o b s t r u c t i o n o f C S F flow in fact occurred, it c a n n o t have been total. O u r t h e r a p e u t i c results c o n f i r m those o f D o n a u e r e t a l . 5. T h e m o s t c o m m o n o p e r a t i v e a p p r o a c h until recently has been f e n e s t r a t i o n o f the cyst into the vent r i c u l a r space, as first suggested b y D a n d y 4. A n o t h e r m e t h o d i n v o l v e d the use o f a c y s t o - p e r i t o n e a l shunt 3. These m o r e e l a b o r a t e m e t h o d s n o l o n g e r seem necessary, as e q u a l l y g o o d results can be o b t a i n e d with a simple i n t e r n a l s h u n t p r o c e d u r e .
Conclusion T h e p r e s e n t cases show t h a t a slender, a p p a r e n t l y n o n - e x p a n s i v e c a v u m h a s the p o t e n t i a l o f increasing its v o l u m e c o n s i d e r a b l y , a n d thus interfere with C S F flow. H o w e v e r , we d o n o t k n o w h o w f r e q u e n t l y this occur. U n t i l the incidence o f such t r a n s i t i o n s is established, we r e c o m m e n d a careful f o l l o w - u p o f children with persisting cava. T r e a t m e n t involving stereotactic i n t r o d u c t i o n o f a c a t h e t e r as a n i n t e r n a l s h u n t 1' 5 is simple, a c c u r a t e a n d effective.
References 1. Backlund E-O (1987) Stereotactic catheter insertion: a new technique. Neurol Res 9:147-150
2. Blom R etal (1986) Demonstration of a symptomatic intraventricular cyst using direct intraventricular metrizamide instillation. AJNR 7:1093-1095 3. Comninos S, Prodromou N, Archondakis G (1985) Primary cystic midline lesions of the brain in childhood. Acta Neurochir [-Suppl] 35:80-83 4. Dandy WE (1931) Congenital cerebral cysts of cavum septi pellucidi (fifth ventricle) and cavum vergae (sixth ventricle). Arch Neuro Psychiat 25:44-66 5. Donauer E, Moringlane JR, Ostertag CB (1986) Cavum Vergae cyst as a cause of hydrocephalus, "almost forgotten" ? Successful stereotactie treatment. Acta Neurochir (Wien) 83:12-19 6. Farruggia S, Babcock DS (1981) The cavum septi pellucidi: Its appearance and incidence with cranial ultrasonography in infancy. Radiology 139:147-150 7. Knudtzon J, Waaler PE, Skj~ervenR, Solberg LK, Steen J (1988) Nye norske percentilkurver for hoyde, vekt og hodeomkrets for alderen 0-17 gtr. Tidsskr Nor L~egeforen 108:2125-2135 8. Larroche JC, Baudey J (1961) Cavum septi lucidi, eavum Vergae, cavum veli interpositi: caviti6 de la ligne m6diane, l~tude anatomique et pneumoene6phalographique dans la periode n6onatale. Biologia Neonat 3:193-236 9. Lewtas N (1987) The central nervous system: Anatomy, pathology and methods of investigation. In: Sutton D (ed) A textbook of radiology and imaging. Livingstone, Edinburgh, p 1418 10. Macpherson P, Teasdale E (1988) CT demonstration of a 5th ventricle - a finding to KO boxers? Neuroradiology 30: 506510 11. Nakano S, Hojo H, Kataoka K, Yamasaki S (1981) Age related incidence of cavum septi pellucidi and cavum Vergae on CT scans of pediatric patients. J Comput Assist Tomogr 5: 348349 12. Pendergrass EP, Hodes PJ (1935) Dilatations of the cavum septi pellucidi and cavum vergae. Ann Surg 101 : 269-295 13. Shaw C-M, Alvord EC (1969) Cava septi pellucidi et Vergae: Their normal and pathological states. Brain 92:213-224 14. Schwidde JT (1952) Incidence ofcavum septi pellucidi and cavum Vergae in 1032 human brains. Arch Neurol Psychiat 67: 625632 15. Van Wagenen WP, Aird RB (1934) Dilatations of the cavity of the septum pellucidum and cavum vergae. Report of cases. Am J Cancer 20:539-557 Correspondence and Reprints: Dr. K. Wester, Department of Neurosurgery, Haukeland Sykehus, N-5021 Bergen, Norway.
Acta Neurochir (Wien) (1990) 104:147-150
© by Springer-Verlag 1990
Dynamic Aspects of Expanding Cava septi pellucidi et Vergae K. Wester 1, P.-H. Pedersen l, J. L. Larsen 2, and P. E. Waaler 3 1Department of Neurosurgery, 2Department of Radiology, Neuroradiology Section, 3Department of Pediatrics, University of Bergen, School of Medicine (Haukeland Hospital), Bergen, Norway
Summary
Methods
Two paediatric patients with expanding cysts of the cava Vergae et septi pellucidi are presented. In the first patient, consecutive CT scans showed a growing cavum thought to be responsible for his dramatic increase in head circumference. In the other patient, the expanding cavum was discovered because a routine skull X-ray after minor head trauma revealed marked impressiones digitatae. Both patients were successfully treated with stereotactically placed internal shunts from the cysts via the lateral ventricle to the subarachnoid space. During this procedure, contrast medium was instilled, and the cysts were visualized on postoperative CT scans. Some dynamic aspects of such expanding cava are discussed.
We chose a surgical approach that was slightly modified from the one reported by Donauer et al. 5. Using the Leksell stereotactic system, the cava were punctured and diluted contrast medium, Iohexol (Omnipaque ®), was instilled to obtain CT-visualization of the cysts. In one patient (Case 1), a CT scan was performed at this stage of the procedure (Fig, 1). Then, an angled Holter ventricular catheter
Keywords: Cavum Vergae; cavum septi pellucidi; cerebral cysts; cerebral ventricles; hydrocephalus; shunt; stereotactie techniques.
Introduction T h e c a v u m V e r g a e a n d the c a v u m septi pellucidi, c o n f l u e n t fluid c o m p a r t m e n t s i n t e r p o s e d between the third ventricle a n d the c o r p u s callosum, are r e g u l a r findings in p r e m a t u r e n o r m a l b r a i n s a n d at birth, b u t b e c o m e g r a d u a l l y less frequent in c h i l d h o o d a n d adolescence 6, 8, 13 Persistent, a s y m p t o m a t i c c a v a are o c c a s i o n a l l y f o u n d on C T scans or at autopsies. M o r e rarely, enl a r g e d c a v a a s s u m i n g a cystic a p p e a r a n c e are found. Such cysts are believed to be o f s o m e clinical significance, as they m a y interfere with the i n t e r n a l d r a i n a g e o f C S F , thus causing h y d r o c e p h a l u s . H o w e v e r , the socalled colloid cysts o f the t h i r d ventricle m o r e often pose clinical p r o b l e m s , p o s s i b l y b e c a u s e they are m o r e p r o n e to give d r a m a t i c s y m p t o m s t h a n the c a v a cysts. T w o p a e d i a t r i c p a t i e n t s are r e p o r t e d , b o t h with clinical a n d r a d i o l o g i c a l signs o f increased i n t r a c r a n i a l pressure, a s s u m e d to be caused b y m a r k e d e n l a r g e m e n t o f the c a v a septi pellucidi et Vergae. O b s e r v a t i o n s m a d e in one o f the p a t i e n t s m a y shed s o m e light on the d y n a m i c aspects o f c a v a cyst d e v e l o p m e n t .
Fig. 1. Case 1. Intra-operative horizontal CT scans after stereotactic filling of the cyst with contrast medium. Note small amount of air in the anterior upper portion of the expanded cava septi pellucidi et Vergae
148
K. Wester et al. : Dynamic Aspects of Expanding Cave septi pellucidi et Vergae
Head circumference (cm)
OP. 60.
55,
50
:y;:;
45-
.. .-
40-
Fig. 4. Case 1. Horizontal CT scans 4 days (left) and 3 months after stereotactic insertion of an internal (cysto-ventriculo-subarachnoidal) shunt
35-
I
2
~
4 ; Months
~(oi'2 AGE
i //
2~
i
~ Years
Fig. 2. Case 1. Graph showing rapid increase in head circumference, and stabilization after the internal shunt procedure (arrow). The other lines represent the 2, 5, 50, and 97.5 percentiles in a Norwegian population of boys 7
was permanently placed into the cyst via the right lateral ventricle by stereotactic techniques. The length of the catheter was selected to match the distance from the burr hole to the postero-inferior border of the cavum Vergae, as measured from the CT scans. Additional side holes were cut in those parts of the catheter expected to be located in the lateral ventricle and the subarachnoid space, thus making the catheter a cysto-ventriculo-subarachnoid shunt. When the catheter reached the center of the cyst, the stylet was withdrawn, and the tip of the flexible catheter was introduced further into the posterior part. The extracranial part of the catheter was then ligated and secured to the periosteum by non-absorbable sutures. The other patient (Case 2), was subjected to a similar procedure, with the exception that the permanent catheter was implanted immediately after the injection of contrast medium into the cyst. The CT scanning was thus performed postoperatively.
Fig. 5. Case2. Preoperative coronal MR scan showing a cystic expansion of the cavum septi pellucidi
Case Descriptions and Results Case 1
This two and a half year old boy had a rapidly increasing head circumference from the age of 4 months (Fig. 2). As the patient showed no clinical signs of raised intracranial pressure and there
Fig. 3. Case l. Horizontal CT scans from nearly identical levels showing the development of an apparently non-expanding enlargement of the cava septi pellucidi et Vergae into an expansive cyst. Left: 10 months old. Middle: 13 months old. Right: 2 years, 1 month old. The cyst showed no further increase at the time of operation 3 months later
K. Wester et al. : Dynamic Aspec~.s of Expanding Cava septi pellucidi et Vergae
Fig. 6. Case2. Postoperative CT scans. Left: The immediate postoperative status. Note contrast medium in the collapsed cavum Vergae portion of the cyst, the catheter leaving the cyst, and air in the anterior portion. Right: 3 months postoperatively
was a family history of large heads, no other measures were undertaken for the following months apart from frequent check-ups, including CT scans. At the age of 9 months, the deviation of the head circumference had reached 1.1 cm above the 97.5 percentile, climbing to nearly 4cm at the age of 21/a years. Simultaneously, CT scans showed a continuously increasing size of the combined cava septi pellucidi et Vergae. The cava were already present in the first scans (Fig. 3). The transverse diameter of the cavity had eventually increased from 6 to 26 mm during the time of observation. This corresponds to a large increase of the cava volume, as they gradually assumed the shape of a sphere. Clinically, the patient showed no other signs of raised intracranial pressure than the increasing head circumference, his psychomotor development being adequate for age. The only conceivable explanation of the patient's growing head was a mild hydrocephalus, induced by the ballooning cava. Therefore, the internal shunt procedure (see Methods) was performed at the age of 2 years and 5 months. As a consequence, the cava collapsed (Fig. 4), the head circumference stabilized and has now remained unchanged for more than 12 months (Fig. 2). The boy is completely healthy. Case 2 At the age of 8 years, the second patient (also a boy) was admitted after a minor head injury. A routine X-ray of the skull showed marked irnpressiones digitatae, and it was found that during the previous year he had noticed impaired vision in one eye and brief episodes of unsteady gait, most probably due to a mild ataxia. A CT scan, and subsequently an MRI scan were therefore performed, showing moderate hydrocephalus and a cyst in the region of the cava septi pellucidi et Vergae (Fig. 5). The transverse diameter of the cyst was 32 ram. After the implantation of the internal shunt, the cyst collapsed, the radiological signs of hydrocephalus became less pronounced (Fig. 6), and the patient no longer experienced the episodes of unsteady gait.
Discussion
The course of one of the patients (Case 1), demonstrates the dynamic aspect of cystic cava septi pellucidi et Vergae. Over a period of 19 months, consec-
149
utive CT scans clearly showed that the cyst size changed dramatically. From being in principle an embryological remnant of no pathological significance, the cave in this case gradually expanded. It is reasonable to assume that the progressively increasing head circumference could be causally related to the enlargment of the cava, since this increase ceased following the internal shunt procedure which induced the collapse of the cava. However, the fact that the head circumference began to increase before the cava became radiologically expanded is intriguing. If the patient's hydrocephalus had some other cause than the enlarging cava, it is difficult to explain why an internal (cysto-ventriculo-subarachnoid) shunt could bring this process to an end. Two possible sequential processes may have been causative, first hydrocephalus of unknown aetiology, leading to a gradual expansion of the pre-existing cava, for example by means of a one-way valve mechanism. Once enlarged, the cava in their turn may have contributed to the progression of the hydrocephalus by obstructing the drainage from the lateral ventricles. Whatever the pathogenesis, a similar process may have occurred in the other patient prior to admission. For obvious reasons, it was not possible to obtain radiological evidence for this assumption. Persistent cava septi pellucidi et Vergae ("5th and 6th ventricles of the brain") are not infrequently tbund at routine examinations of human brains 91 - 1,13,14.Most of these cysts are small, their incidence declines with increasing age 13, and they are generally of no pathological significance. More rarely, such cysts obviously expand, probably a causative factor in the inadequate CSF drainage in these patients a' 4, 5, 12, 15 Shaw and Alvord ~3 distinguished between: 1) incidental, asymptomatic cysts, and 2) symptomatic cysts with increased pressure within the cyst. The observations in one of our patients indicate that there may be transitions between the two groups, and that a previously non-expanding cavity may develop into an expanding one. If children with persistent cava septi pellucidi et Vergae were followed routinely with CT or MRI scans, the pathogenesis of such a transition could be clarified. In the relevant literature, the lack of references and the age of the few papers most frequently cited (see e.g. 6, 10) are striking features, in sharp contrast to regularly appearing, numerous reports on colloid cysts of the third ventricle. In the Cumulated Index Medicus 1981-1988 (volumes 22-29), "colloid cysts" are mentioned nearly ten times more often than "cava septi pellucidi et/aut Vergae" or equivalent terms (37 vs. 4).
150
K. Wester et al.: Dynamic Aspects of Expanding Cava septi pellucidi et Vergae
B o t h processes are l o c a t e d at a critical level for C S F d r a i n a g e , a n d s h o u l d thus have the p o t e n t i a l o f p r o ducing d r a m a t i c s y m p t o m s if c o m p r o m i s i n g the C S F flow. T h e o b s e r v e d scarceness o f r e p o r t s on c a v a cysts in the l i t e r a t u r e m a y c a r r y s o m e i m p o r t a n c e . It m a y reflect t h a t s y m p t o m a t i c c a v a cysts in fact a p p e a r infrequently, b u t it m a y also reflect t h a t p o s s i b l y occurring s y m p t o m s f r o m these cysts are t o o v a g u e to be clinically recognized, in c o n t r a s t to w h a t is c o m m o n with colloid cysts. T h e p r e s e n t two cases illustrate this. T h e c o m b i n a t i o n o f relatively m i l d s y m p t o m s in o u r p a t i e n t s a n d the c o n s i d e r a b l e size o f their cysts is striking. I f o b s t r u c t i o n o f C S F flow in fact occurred, it c a n n o t have been total. O u r t h e r a p e u t i c results c o n f i r m those o f D o n a u e r e t a l . 5. T h e m o s t c o m m o n o p e r a t i v e a p p r o a c h until recently has been f e n e s t r a t i o n o f the cyst into the vent r i c u l a r space, as first suggested b y D a n d y 4. A n o t h e r m e t h o d i n v o l v e d the use o f a c y s t o - p e r i t o n e a l shunt 3. These m o r e e l a b o r a t e m e t h o d s n o l o n g e r seem necessary, as e q u a l l y g o o d results can be o b t a i n e d with a simple i n t e r n a l s h u n t p r o c e d u r e .
Conclusion T h e p r e s e n t cases show t h a t a slender, a p p a r e n t l y n o n - e x p a n s i v e c a v u m h a s the p o t e n t i a l o f increasing its v o l u m e c o n s i d e r a b l y , a n d thus interfere with C S F flow. H o w e v e r , we d o n o t k n o w h o w f r e q u e n t l y this occur. U n t i l the incidence o f such t r a n s i t i o n s is established, we r e c o m m e n d a careful f o l l o w - u p o f children with persisting cava. T r e a t m e n t involving stereotactic i n t r o d u c t i o n o f a c a t h e t e r as a n i n t e r n a l s h u n t 1' 5 is simple, a c c u r a t e a n d effective.
References 1. Backlund E-O (1987) Stereotactic catheter insertion: a new technique. Neurol Res 9:147-150
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