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A large arachnoid cyst of the lateral ventricle extending from the supracerebellar cistern—case report
Surgical Neurology 65 (2006) 611 – 614 www.surgicalneurology-online.com
Arachnoid Cyst
A large arachnoid cyst of the lateral ventricle extending from the supracerebellar cistern—case report Seoung Woo Park, MDa, Soo Han Yoon, MDb,*, Ki Hong Cho, MDb, Yong Sam Shin, MDb a
Department of Neurosurgery, Kangwon National University, College of Medicine, Chunchon 200-701, South Korea b Department of Neurosurgery, Ajou University School of Medicine, Suwon 443-721, South Korea Received 23 May 2005; accepted 30 July 2005
Abstract
Background: The pathogenetic mechanism of intraventricular arachnoid cyst development is still controversial, but is believed to originate from the vascular mesenchyme or as an extension of the arachnoid cyst in the subarachnoid space into the ventricle through the choroidal fissure. We report a case supporting the extension hypothesis and suggest differential points between an intraventricular arachnoid cyst that extended from the supracerebellar space and a lateral ventricular diverticulum that extended into the supracerebellar cistern. Case Description: A 12-month-old girl presented with macrocephaly and developmental delay. Her magnetic resonance imaging showed an arachnoid cyst that had developed from the supracerebellar space in the posterior fossa, and which extended into the left lateral ventricle resulting in expansion of the left lateral ventricle and displacing the choroids plexus anteriorly and laterally and the midline to the right. We treated an intraventricular arachnoid cyst by endoscopic fenestration resulting in dramatic reduction of the intraventricular arachnoid cyst with large bilateral subdural fluid collection. We performed a subduroperitoneal shunt for subdural fluid collection and subsequent cystoperitoneal shunt for the remnant cyst. Conclusion: We suggest that this case supports the extension hypothesis from the subarachnoid space through the choroidal fissure into the lateral ventricle. We also suggest that one of the radiological differential points between an intraventricular arachnoid cyst and a ventricular diverticulum is displacement and compression of the choroid plexus of the lateral ventricle. D 2006 Elsevier Inc. All rights reserved.
Keywords:
Intraventricular arachnoid cyst; Hydrocephalus; Macrocrania; Intracranial pressure
1. Introduction Intracranial arachnoid cysts have rarely been found in the ventricle or intradiploic space in patients without any communication with the subarachnoid space. The precise pathogenetic mechanisms involved in the formation of intraventricular arachnoid cysts are as yet unknown. Yeates and Enzmann [23] have suggested that intraventricular arachnoid cyst may originate from the vascular mesenchyme of the choroids plexus, whereas Nakase et al [11] postulated that the intraventricular arachnoid cyst may be an extension of the arachnoid cyst in the subarachnoid space into the Abbreviations: CT, computed tomogram; MR, magnetic resonance. T Corresponding author. Tel.: +82 31 219 5233; fax: +82 31 219 5238. E-mail addresses: [email protected], [email protected] (S.H. Yoon). 0090-3019/$ – see front matter D 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.surneu.2005.07.069
lateral ventricle through the choroidal fissure. However, there has been no such reported confirmative case in the literature that has demonstrated definite extension of an arachnoid cyst from the subarachnoid space into the lateral ventricle through the choroidal fissure. This extension route would be the reversed route of the lateral ventricular diverticulum into the supracerebellar cistern. We describe a case showing clear extension of arachnoid cyst from the supracerebellar subarachnoid space into the lateral ventricle with differential points from a lateral ventricular diverticulum that extended into the supracerebellar cistern.
2. Case report A 12-month-old girl presented with macrocephaly and developmental delay. Her CT and MR imaging showed an
612
S.W. Park et al. / Surgical Neurology 65 (2006) 611 – 614
arachnoid cyst that had developed from the supracerebellar space in the posterior fossa, and which extended into the antrum and temporal horn of the left lateral ventricle resulting in expansion of the antrum and temporal horn of the left lateral ventricle (Fig. 1). The axial MR imaging showed that the path of the cyst enlarged the velum interpositum resulting in a large hole in the lateral ventricle (Fig. 1A). This cyst displaced and compressed the anterior horn of the left lateral ventricle anteriorly and the right choroid plexus laterally (Fig. 1B). This cyst also severely displaced the left choroid plexus anteriorly and inferiorly (Fig. 1C). The coronal MR images showed that the midline
structures including internal cerebral veins and the medial walls of the lateral ventricle were displaced to the contralateral side (Fig. 1D). Cerebrospinal fluid flow in the right lateral ventricle was also impeded by this midline displacement from the expanded cyst of the left lateral ventricle resulting in simultaneous dilatation of the right lateral ventricle. The right choroid plexus and choroidal vessels were compressed and displaced laterally (Fig. 1E). The right choroid plexus, the branching portion of the choroidal vessels, and left choroidal vessels were all displaced and collapsed on the ventricular surface (Fig. 1F). The sagittal MR images showed that this cyst dilated the velum interpositum upwardly to the corpus callosum and compressed the cerebellum inferiorly, resulting in a compressed small cerebellum (Fig. 1G). The cyst enlarged the supracerebellar cistern and cerebellar herniation into the spinal canal with a dilated central canal of the cervical spinal cord (Fig. 1H). She underwent endoscopic fenestration of the intraventricular arachnoid cyst by establishment of an interventricular window between the lateral ventricles. During endoscopic fenestration, we did not observe any evidence of a definite cystic capsule in the lateral ventricle. The intraventricular pressure dramatically decreased after the endoscopic fenestration. After 1 month, we found the presence of a bilateral large subdural fluid collection on the follow-up CT scan that resulted from severe reduction of the intraventricular arachnoid cyst and from insufficient brain expansion. The bilateral large subdural fluid collection was treated by a subduroperitoneal shunt, which then disappeared, but the intraventricular arachnoid cyst remained in the temporoparietal area at 1-year follow-up CT scan. The patient underwent a cystoperitoneal shunt to remove the remnant temporoparietal intraventricular arachnoid cyst that resulted in further reduction in size. She has been followed up for 5 years to date without any recurrent enlargement of the intraventricular temporal cyst. She has recovered her
Fig. 1. Initial MR imaging shows that the arachnoid cyst had developed from the supracerebellar space in the posterior fossa and extended into the antrum and temporal horn of the left lateral ventricle. A and B: Axial MR imaging shows that the intraventricular cyst displaces the left choroidal vessels anteriorly (small arrow heads), the right choroid plexus laterally (small arrow), the midline vessels to the right (large arrow), and an enlarged velum interpositum. C: Axial MR imaging shows that the left choroid plexus (small arrow) was severely displaced anteriorly and the thin cystic wall (arrow head) crossed the right lateral ventricle. D and E: Coronal MR images show that the cyst (small arrow heads) displaces the left choroids plexus contralaterally (arrow) and the right choroid plexus and choroidal vessels laterally (large arrow head). F: Coronal MR images shows displaced and collapsed right choroids plexus (small arrow), branching portion of choroidal vessels (large arrow), and left choroidal vessels (arrow head). G: Sagittal MR imaging shows that the cyst of the posterior fossa depressing the cerebellum downwardly (arrows) extending into and dilating the velum interpositum (small arrow heads) with anteriorly displaced contralateral choroid plexus (large arrow). H: Sagittal MR imaging shows the herniation of cerebellum (arrow) with visualization of the central canal of the cervical spinal cord (arrow heads).
S.W. Park et al. / Surgical Neurology 65 (2006) 611 – 614
normal daily activity, but mild intellectual deterioration is suspected, reflected by an intellectual quotient of 95.
3. Discussion Arachnoid cysts are usually were found incidentally 0.1% to 0.4% in the general population and comprises approximately 1% of all intracranial space-occupying lesions [18-20]. Intraventricular arachnoid cysts were present in 4 among 54 fetal cysts diagnosed with prenatal fetal ultrasonography according to Pierre-Kahn et al [14]. A total of 22 cases of lateral ventricular arachnoid cysts have been found in a MEDLINE search [2,3,5-9,11-13, 17,21-24]. Among these 22 lateral ventricular arachnoid cysts, there were 7 cases of pediatric lateral ventricular arachnoid cysts, all of which occurred in males compared with the authors’ case who was female [2,6,8,12,24]. There have been many previous reports of macrocrania, focal enlargement of the skull, intracranial hypertension, intracranial bleeding, paralysis, and seizure as manifesting symptoms of an arachnoid cyst in the subarachnoid space [15]. The presence of lateral ventricular arachnoid cysts was demonstrated in 5 cases of macrocephaly and in 1 case of seizure in a group of 8 pediatric patients (including the authors’ case), compared with 15 cases of lateral ventricular arachnoid cyst in adults who presented with headache in 9 cases, seizure attacks in 2 cases, gait disturbance in 1 case, and incidental findings in 2 cases [2,3,5-9,11-13,17,21-24]. For the treatment of intraventricular arachnoid cysts, shunt procedure only was performed in only 1 of all 8 pediatric and 15 adult lateral ventricular arachnoid cysts (including authors’ case). Kurokawa et al [6] recommended cyst resection rather than the shunt procedure because he found that the size of the intraventricular arachnoid cyst was not reduced after the shunt operation. Shunt malfunctions in patients with the lateral ventricular arachnoid cyst were probably more common compared with patients with hydrocephalus because the cyst wall could wrap around the proximal shunt catheter resulting in shunt malfunction when the arachnoid cyst collapsed. Some authors have advocated open cyst removal especially for fourth ventricular arachnoid cysts [1,10]. Other authors also have recommended the combined approach of shunt and open fenestration or endoscopic fenestration for the lateral ventricular arachnoid cysts [8,12]. In the review of 7 pediatric arachnoid cyst cases of the lateral ventricular arachnoid cyst in the literature, the patients were treated with cystoperitoneal shunt in 1 case, fenestration in 2 cases, fenestration and shunt in 2 cases, endoscopic fenestration in 1 case, endoscopic fenestration and shunt in 1 case, and shunt and open removal in 1 case. If the authors’ case is included, the combined approach totals 5 cases [2,6,8,12,24]. In the literature that describes 15 adult arachnoid cysts of the lateral ventricle, the patients were treated with open cyst removal in 2 cases, open fenestration or partial cyst removal in 7 cases, endoscopic fenestration in
613
2 cases, fenestration and shunt in 2 cases, and no treatment in 2 cases [3,5,7,9,11,13,17,21-23]. From this study, the authors suggest that endoscopic fenestration of an extremely large intraventricular arachnoid cyst with high pressure could result in rare post-decompression subdural fluid collection. All conditions related with slow brain expansion or growth and rapid cyst reduction could be contributing factors to result in post-endoscopic fenestration subdural fluid collection. Cystoperitoneal shunting with a high pressure or programmable valve may be safer than fenestration to prevent large postoperative subdural fluid collection for large arachnoid cyst with high pressure. Pathogenetic mechanisms involved in the formation of arachnoid cysts in the arachnoid space have not been clearly elucidated. It is suspected to develop from anomalous splitting and duplication of the arachnoid during normal arachnoid space development, when fluid develops in the subarachnoid space at the 15th week of gestation after development of the dura, arachnoid, and pia from loose primitive mesenchyme surrounding the neural tube [15,16]. Most arachnoid cysts are located in the normal arachnoid cistern, and this also suggests that arachnoid cyst development is an error of arachnoid splitting during cistern formation. Developmental mechanisms of intraventricular arachnoid cysts are also as yet unknown, but Yeates and Enzmann [23] have suggested that intraventricular arachnoid cyst may originate from the vascular mesenchyme because they were able to observe an intraventricular arachnoid cyst attached to the choroid plexus with pathological mesenchymal components of the choroid plexus present in the wall of the arachnoid cyst. Nakase et al [11] reported two intraventricular arachnoid cysts and suggested that intraventricular arachnoid cyst may have extended from the arachnoid cyst in the subarachnoid space into the lateral ventricle through the choroidal fissure. However, there has been no confirmative case in the literature that describes
Fig. 2. Schematic illustration to explain the differences between an intraventricular arachnoid cyst (A) that extends from the supracerebellar space and lateral ventricular diverticulum (B) that extends into the supracerebellar cistern from unilateral obstruction of the foramen of Monro. Both may show a dilated lateral ventricle, displaced midline to contralateral side, and supracerebellar cyst communicating with the lateral ventricle. They differ in that the intraventricular arachnoid cyst displaces and compresses the choroid plexus (arrow), whereas the ventricular diverticulum does not show any compression or displacement of the choroid plexus (arrows).
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extension of an arachnoid cyst from the subarachnoid space into the lateral ventricle through the choroidal fissure. The above case of arachnoid cyst does not support the hypothesis of Yeates and Enzmann [23] because there was no evidence for hypertrophy of the choroidal plexus mesenchyme that could suggest the origin of intraventricular arachnoid cyst. This arachnoid cyst showed clear extension from the supracerebellar subarachnoid space into the lateral ventricle. A rare intraventricular arachnoid cyst that extends from the supracerebellar space has similar radiological findings with common lateral ventricular diverticulum that extends into the supracerebellar cistern, especially from unilateral obstruction of the foramen of Monro [4]. Both may show a dilated lateral ventricle, displaced midline to the contralateral side, and a supracerebellar cyst. The ventricular diverticulum extends into the supracerebellar space via the tela choroidea communicating supracerebellar cistern with the lateral ventricle. The intraventricular arachnoid cyst extends reversely from the supracerebellar space through the route of the ventricular diverticular extension. However, we suggest that the intraventricular arachnoid cyst displaces and compresses the choroid plexus, whereas the ventricular diverticulum does not show any compression or displacement of the choroid plexus (Fig. 2). The above case showed compression and displacement of the choroid plexus of the dilated lateral ventricle that suggests that the arachnoid cyst extended from the other subdural space. We conclusively suggest that this arachnoid cyst extended from the supracerebellar space and support the extension hypothesis of Nakase et al [11]. 4. Conclusion We suggest that this case supports the extension hypothesis in that intraventricular arachnoid cyst originated from extension of the arachnoid cyst in the subdural space. We also suggest that displacement and compression of the choroid plexus in the lateral ventricle could be differential points between the intraventricular arachnoid cyst and ventricular diverticulum. References [1] Acar O, Kocaogullar Y, Guney O. Arachnoid cyst within the fourth ventricle: a case report. Clin Neurol Neurosurg 2003;105:93 - 4. [2] Fritsch MJ, Mehdorn M. Endoscopic intraventricular surgery for treatment of hydrocephalus and loculated CSF space in children less than one year of age. Pediatr Neurosurg 2002;36:183 - 8.
[3] Goda K, Tsunoda S, Sakaki T, et al. Intraventricular arachnoid cyst appearing with attacks of orbital pain: case report and review of the literature. No Shinkei Geka 1990;18:757 - 60. [4] Jabaudon D, Charest D, Porchet F. Pathogenesis and diagnostic pitfalls of ventricular diverticula: case report and review of the literature. Neurosurgery 2003;52:209 - 12. [5] Koga H, Mukawa J, Miyagi K, et al. Symptomatic intraventricular arachnoid cyst in an elderly man. Acta Neurochir (Wien) 1995;137: 113 - 7. [6] Kurokawa Y, Sohma T, Tsuchita H, et al. A case of intraventricular arachnoid cyst. How should it be treated? Childs Nerv Syst 1990; 6:365 - 7. [7] Lee KS, Bae HG, Yun IG. Intraventricular arachnoid cyst. J Neurosurg 1989;70:154 - 5. [8] Martinez-Lage JF, Poza M, Sola J, et al. Congenital arachnoid cyst of the lateral ventricles in children. Childs Nerv Syst 1992;8:203 - 6. [9] Maiuri F, Iaconetta G, Ganemi M, et al. Intraventricular arachnoid cyst. Report of two cases. J Neurosurg 1988;68:482 - 6. [10] Nadkarni T, Hande A, Nagpal R. Arachnoid cyst within the fourth ventricle—a case report. Br J Neurosurg 1995;9:675 - 8. [11] Nakase H, Hisanaga M, Hashimoto S, et al. Intraventricular arachnoid cyst. Report of two cases. J Neurosurg 1988;68:482 - 6. [12] Okamura K, Watanabe M, Inoue N, et al. Intraventricular arachnoid cyst—on the origin of intraventricular arachnoid cysts. No To Shinkei 1996;48:1015 - 21. [13] Pelletier J, Milandre L, Peragut JC, et al. Intraventricular choroid plexus barachnoidQ cyst. MRI findings. Neuroradiology 1990;32:523 - 5. [14] Pierre-Kahn A, Hanlo P, Sonigo P, et al. The contribution of prenatal diagnosis to the understanding of malformative intracranial cysts: state of the art. Childs Nerv Syst 2000;16:619 - 26. [15] Raffel C, McComb JG. Arachnoid cysts. In: American society of pediatric neurosurgeons section of pediatric neurosurgery of the A.A.N.S., editor. Pediatric Neurosurgery. Philadelphia7 WB Saunders; 1994. p. 104 - 10. [16] Santamarta D, Aguas J, Ferrer E. The natural history of arachnoid cysts: endoscopic and cine-mode MRI evidence of a slit-valve mechanism. Minim Invasive Neurosurg 1995;38:133 - 7. [17] Seike M, Kurisaka M, Mori K. Intraventricular arachnoid cyst. Case report. Neurol Med Chir (Tokyo) 1987;27:154 - 8. [18] Shaw CM, Alvord EC. Congenital arachnoid cysts and their differential diagnosis. In: Vihken PJ, Bruyn GW, editors. Congenital malformation of the brain and skull. Part II. Amsterdam7 Elsevier North-Holland; 1977. p. 75 - 135. [19] Shuangshoti S. Calcified congenital arachnoid cyst with heterotopic neuroglia in wall. J Neurol Neurosurg Psychiatry 1978;41:88 - 94. [20] Tamaki N, Taomoto K, Fujiwara K, et al. Temporal arachnoid cysts in children—neuroradiological and etiological considerations. No To Shinkei 1976;28:937 - 50. [21] Wong CW, Ko SF, Wai YY. Arachnoid cyst of the lateral ventricle manifesting positional psychosis. Neurosurgery 1993;32:841 - 3. [22] Yamamoto M, Oka K, Takasugi S, et al. Flexible neuroendoscopy for percutaneous treatment of intraventricular lesions in the absence of hydrocephalus. Minim Invasive Neurosurg 1997;40:139 - 43. [23] Yeates A, Enzmann D. An intraventricular arachnoid cyst. J Comput Assist Tomogr 1979;3:697 - 700. [24] Yoshida T, Ikeda T, Maeda Y, et al. An arachnoid cyst in the left lateral ventricle. No Shinkei Geka 1984;12:969 - 73.
Arachnoid Cyst
A large arachnoid cyst of the lateral ventricle extending from the supracerebellar cistern—case report Seoung Woo Park, MDa, Soo Han Yoon, MDb,*, Ki Hong Cho, MDb, Yong Sam Shin, MDb a
Department of Neurosurgery, Kangwon National University, College of Medicine, Chunchon 200-701, South Korea b Department of Neurosurgery, Ajou University School of Medicine, Suwon 443-721, South Korea Received 23 May 2005; accepted 30 July 2005
Abstract
Background: The pathogenetic mechanism of intraventricular arachnoid cyst development is still controversial, but is believed to originate from the vascular mesenchyme or as an extension of the arachnoid cyst in the subarachnoid space into the ventricle through the choroidal fissure. We report a case supporting the extension hypothesis and suggest differential points between an intraventricular arachnoid cyst that extended from the supracerebellar space and a lateral ventricular diverticulum that extended into the supracerebellar cistern. Case Description: A 12-month-old girl presented with macrocephaly and developmental delay. Her magnetic resonance imaging showed an arachnoid cyst that had developed from the supracerebellar space in the posterior fossa, and which extended into the left lateral ventricle resulting in expansion of the left lateral ventricle and displacing the choroids plexus anteriorly and laterally and the midline to the right. We treated an intraventricular arachnoid cyst by endoscopic fenestration resulting in dramatic reduction of the intraventricular arachnoid cyst with large bilateral subdural fluid collection. We performed a subduroperitoneal shunt for subdural fluid collection and subsequent cystoperitoneal shunt for the remnant cyst. Conclusion: We suggest that this case supports the extension hypothesis from the subarachnoid space through the choroidal fissure into the lateral ventricle. We also suggest that one of the radiological differential points between an intraventricular arachnoid cyst and a ventricular diverticulum is displacement and compression of the choroid plexus of the lateral ventricle. D 2006 Elsevier Inc. All rights reserved.
Keywords:
Intraventricular arachnoid cyst; Hydrocephalus; Macrocrania; Intracranial pressure
1. Introduction Intracranial arachnoid cysts have rarely been found in the ventricle or intradiploic space in patients without any communication with the subarachnoid space. The precise pathogenetic mechanisms involved in the formation of intraventricular arachnoid cysts are as yet unknown. Yeates and Enzmann [23] have suggested that intraventricular arachnoid cyst may originate from the vascular mesenchyme of the choroids plexus, whereas Nakase et al [11] postulated that the intraventricular arachnoid cyst may be an extension of the arachnoid cyst in the subarachnoid space into the Abbreviations: CT, computed tomogram; MR, magnetic resonance. T Corresponding author. Tel.: +82 31 219 5233; fax: +82 31 219 5238. E-mail addresses: [email protected], [email protected] (S.H. Yoon). 0090-3019/$ – see front matter D 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.surneu.2005.07.069
lateral ventricle through the choroidal fissure. However, there has been no such reported confirmative case in the literature that has demonstrated definite extension of an arachnoid cyst from the subarachnoid space into the lateral ventricle through the choroidal fissure. This extension route would be the reversed route of the lateral ventricular diverticulum into the supracerebellar cistern. We describe a case showing clear extension of arachnoid cyst from the supracerebellar subarachnoid space into the lateral ventricle with differential points from a lateral ventricular diverticulum that extended into the supracerebellar cistern.
2. Case report A 12-month-old girl presented with macrocephaly and developmental delay. Her CT and MR imaging showed an
612
S.W. Park et al. / Surgical Neurology 65 (2006) 611 – 614
arachnoid cyst that had developed from the supracerebellar space in the posterior fossa, and which extended into the antrum and temporal horn of the left lateral ventricle resulting in expansion of the antrum and temporal horn of the left lateral ventricle (Fig. 1). The axial MR imaging showed that the path of the cyst enlarged the velum interpositum resulting in a large hole in the lateral ventricle (Fig. 1A). This cyst displaced and compressed the anterior horn of the left lateral ventricle anteriorly and the right choroid plexus laterally (Fig. 1B). This cyst also severely displaced the left choroid plexus anteriorly and inferiorly (Fig. 1C). The coronal MR images showed that the midline
structures including internal cerebral veins and the medial walls of the lateral ventricle were displaced to the contralateral side (Fig. 1D). Cerebrospinal fluid flow in the right lateral ventricle was also impeded by this midline displacement from the expanded cyst of the left lateral ventricle resulting in simultaneous dilatation of the right lateral ventricle. The right choroid plexus and choroidal vessels were compressed and displaced laterally (Fig. 1E). The right choroid plexus, the branching portion of the choroidal vessels, and left choroidal vessels were all displaced and collapsed on the ventricular surface (Fig. 1F). The sagittal MR images showed that this cyst dilated the velum interpositum upwardly to the corpus callosum and compressed the cerebellum inferiorly, resulting in a compressed small cerebellum (Fig. 1G). The cyst enlarged the supracerebellar cistern and cerebellar herniation into the spinal canal with a dilated central canal of the cervical spinal cord (Fig. 1H). She underwent endoscopic fenestration of the intraventricular arachnoid cyst by establishment of an interventricular window between the lateral ventricles. During endoscopic fenestration, we did not observe any evidence of a definite cystic capsule in the lateral ventricle. The intraventricular pressure dramatically decreased after the endoscopic fenestration. After 1 month, we found the presence of a bilateral large subdural fluid collection on the follow-up CT scan that resulted from severe reduction of the intraventricular arachnoid cyst and from insufficient brain expansion. The bilateral large subdural fluid collection was treated by a subduroperitoneal shunt, which then disappeared, but the intraventricular arachnoid cyst remained in the temporoparietal area at 1-year follow-up CT scan. The patient underwent a cystoperitoneal shunt to remove the remnant temporoparietal intraventricular arachnoid cyst that resulted in further reduction in size. She has been followed up for 5 years to date without any recurrent enlargement of the intraventricular temporal cyst. She has recovered her
Fig. 1. Initial MR imaging shows that the arachnoid cyst had developed from the supracerebellar space in the posterior fossa and extended into the antrum and temporal horn of the left lateral ventricle. A and B: Axial MR imaging shows that the intraventricular cyst displaces the left choroidal vessels anteriorly (small arrow heads), the right choroid plexus laterally (small arrow), the midline vessels to the right (large arrow), and an enlarged velum interpositum. C: Axial MR imaging shows that the left choroid plexus (small arrow) was severely displaced anteriorly and the thin cystic wall (arrow head) crossed the right lateral ventricle. D and E: Coronal MR images show that the cyst (small arrow heads) displaces the left choroids plexus contralaterally (arrow) and the right choroid plexus and choroidal vessels laterally (large arrow head). F: Coronal MR images shows displaced and collapsed right choroids plexus (small arrow), branching portion of choroidal vessels (large arrow), and left choroidal vessels (arrow head). G: Sagittal MR imaging shows that the cyst of the posterior fossa depressing the cerebellum downwardly (arrows) extending into and dilating the velum interpositum (small arrow heads) with anteriorly displaced contralateral choroid plexus (large arrow). H: Sagittal MR imaging shows the herniation of cerebellum (arrow) with visualization of the central canal of the cervical spinal cord (arrow heads).
S.W. Park et al. / Surgical Neurology 65 (2006) 611 – 614
normal daily activity, but mild intellectual deterioration is suspected, reflected by an intellectual quotient of 95.
3. Discussion Arachnoid cysts are usually were found incidentally 0.1% to 0.4% in the general population and comprises approximately 1% of all intracranial space-occupying lesions [18-20]. Intraventricular arachnoid cysts were present in 4 among 54 fetal cysts diagnosed with prenatal fetal ultrasonography according to Pierre-Kahn et al [14]. A total of 22 cases of lateral ventricular arachnoid cysts have been found in a MEDLINE search [2,3,5-9,11-13, 17,21-24]. Among these 22 lateral ventricular arachnoid cysts, there were 7 cases of pediatric lateral ventricular arachnoid cysts, all of which occurred in males compared with the authors’ case who was female [2,6,8,12,24]. There have been many previous reports of macrocrania, focal enlargement of the skull, intracranial hypertension, intracranial bleeding, paralysis, and seizure as manifesting symptoms of an arachnoid cyst in the subarachnoid space [15]. The presence of lateral ventricular arachnoid cysts was demonstrated in 5 cases of macrocephaly and in 1 case of seizure in a group of 8 pediatric patients (including the authors’ case), compared with 15 cases of lateral ventricular arachnoid cyst in adults who presented with headache in 9 cases, seizure attacks in 2 cases, gait disturbance in 1 case, and incidental findings in 2 cases [2,3,5-9,11-13,17,21-24]. For the treatment of intraventricular arachnoid cysts, shunt procedure only was performed in only 1 of all 8 pediatric and 15 adult lateral ventricular arachnoid cysts (including authors’ case). Kurokawa et al [6] recommended cyst resection rather than the shunt procedure because he found that the size of the intraventricular arachnoid cyst was not reduced after the shunt operation. Shunt malfunctions in patients with the lateral ventricular arachnoid cyst were probably more common compared with patients with hydrocephalus because the cyst wall could wrap around the proximal shunt catheter resulting in shunt malfunction when the arachnoid cyst collapsed. Some authors have advocated open cyst removal especially for fourth ventricular arachnoid cysts [1,10]. Other authors also have recommended the combined approach of shunt and open fenestration or endoscopic fenestration for the lateral ventricular arachnoid cysts [8,12]. In the review of 7 pediatric arachnoid cyst cases of the lateral ventricular arachnoid cyst in the literature, the patients were treated with cystoperitoneal shunt in 1 case, fenestration in 2 cases, fenestration and shunt in 2 cases, endoscopic fenestration in 1 case, endoscopic fenestration and shunt in 1 case, and shunt and open removal in 1 case. If the authors’ case is included, the combined approach totals 5 cases [2,6,8,12,24]. In the literature that describes 15 adult arachnoid cysts of the lateral ventricle, the patients were treated with open cyst removal in 2 cases, open fenestration or partial cyst removal in 7 cases, endoscopic fenestration in
613
2 cases, fenestration and shunt in 2 cases, and no treatment in 2 cases [3,5,7,9,11,13,17,21-23]. From this study, the authors suggest that endoscopic fenestration of an extremely large intraventricular arachnoid cyst with high pressure could result in rare post-decompression subdural fluid collection. All conditions related with slow brain expansion or growth and rapid cyst reduction could be contributing factors to result in post-endoscopic fenestration subdural fluid collection. Cystoperitoneal shunting with a high pressure or programmable valve may be safer than fenestration to prevent large postoperative subdural fluid collection for large arachnoid cyst with high pressure. Pathogenetic mechanisms involved in the formation of arachnoid cysts in the arachnoid space have not been clearly elucidated. It is suspected to develop from anomalous splitting and duplication of the arachnoid during normal arachnoid space development, when fluid develops in the subarachnoid space at the 15th week of gestation after development of the dura, arachnoid, and pia from loose primitive mesenchyme surrounding the neural tube [15,16]. Most arachnoid cysts are located in the normal arachnoid cistern, and this also suggests that arachnoid cyst development is an error of arachnoid splitting during cistern formation. Developmental mechanisms of intraventricular arachnoid cysts are also as yet unknown, but Yeates and Enzmann [23] have suggested that intraventricular arachnoid cyst may originate from the vascular mesenchyme because they were able to observe an intraventricular arachnoid cyst attached to the choroid plexus with pathological mesenchymal components of the choroid plexus present in the wall of the arachnoid cyst. Nakase et al [11] reported two intraventricular arachnoid cysts and suggested that intraventricular arachnoid cyst may have extended from the arachnoid cyst in the subarachnoid space into the lateral ventricle through the choroidal fissure. However, there has been no confirmative case in the literature that describes
Fig. 2. Schematic illustration to explain the differences between an intraventricular arachnoid cyst (A) that extends from the supracerebellar space and lateral ventricular diverticulum (B) that extends into the supracerebellar cistern from unilateral obstruction of the foramen of Monro. Both may show a dilated lateral ventricle, displaced midline to contralateral side, and supracerebellar cyst communicating with the lateral ventricle. They differ in that the intraventricular arachnoid cyst displaces and compresses the choroid plexus (arrow), whereas the ventricular diverticulum does not show any compression or displacement of the choroid plexus (arrows).
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extension of an arachnoid cyst from the subarachnoid space into the lateral ventricle through the choroidal fissure. The above case of arachnoid cyst does not support the hypothesis of Yeates and Enzmann [23] because there was no evidence for hypertrophy of the choroidal plexus mesenchyme that could suggest the origin of intraventricular arachnoid cyst. This arachnoid cyst showed clear extension from the supracerebellar subarachnoid space into the lateral ventricle. A rare intraventricular arachnoid cyst that extends from the supracerebellar space has similar radiological findings with common lateral ventricular diverticulum that extends into the supracerebellar cistern, especially from unilateral obstruction of the foramen of Monro [4]. Both may show a dilated lateral ventricle, displaced midline to the contralateral side, and a supracerebellar cyst. The ventricular diverticulum extends into the supracerebellar space via the tela choroidea communicating supracerebellar cistern with the lateral ventricle. The intraventricular arachnoid cyst extends reversely from the supracerebellar space through the route of the ventricular diverticular extension. However, we suggest that the intraventricular arachnoid cyst displaces and compresses the choroid plexus, whereas the ventricular diverticulum does not show any compression or displacement of the choroid plexus (Fig. 2). The above case showed compression and displacement of the choroid plexus of the dilated lateral ventricle that suggests that the arachnoid cyst extended from the other subdural space. We conclusively suggest that this arachnoid cyst extended from the supracerebellar space and support the extension hypothesis of Nakase et al [11]. 4. Conclusion We suggest that this case supports the extension hypothesis in that intraventricular arachnoid cyst originated from extension of the arachnoid cyst in the subdural space. We also suggest that displacement and compression of the choroid plexus in the lateral ventricle could be differential points between the intraventricular arachnoid cyst and ventricular diverticulum. References [1] Acar O, Kocaogullar Y, Guney O. Arachnoid cyst within the fourth ventricle: a case report. Clin Neurol Neurosurg 2003;105:93 - 4. [2] Fritsch MJ, Mehdorn M. Endoscopic intraventricular surgery for treatment of hydrocephalus and loculated CSF space in children less than one year of age. Pediatr Neurosurg 2002;36:183 - 8.
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