Gross and Neurosurgical Anatomy of the Cerebellar Tonsil Clinical Anatomy in Mavridis1*

Page 1 of 6

Critical review

Gross and neurosurgical anatomy of the cerebellar tonsil Clinical Anatomy IN Mavridis1*

Abstract anomalies such as arterial Discussion Introduction hypoplasticity, makes this structure The author has referenced one of its The primary purpose of this review potentially vulnerable to vascular own studies in this review. This was to focus on the gross anatomy, accidents (mainly infarcts) of the referenced study has been conducted in including morphometric inferior cerebellar arteries. A accordance with the Declaration of characteristics and arterial thorough understanding of the Helsinki (1964) and the protocols of vasculature, of the human cerebellar regional tonsillar anatomy, as well as these studies have been approved by tonsil. We also aimed to investigate its relations with the branches of the the relevant ethics committees related the neurosurgical anatomy of this posterior inferior cerebellar artery is to the institution in which they were clinically important structure of the of paramount significance for performed. human brain. neurosurgical interventions in this Discussion area. Gross anatomy The cerebellar tonsil is a rounded Morphology, locations and relations lobule on the undersurface of each Introduction The cerebellar tonsil is a rounded cerebellar hemisphere, continuous The human cerebellar tonsil is famous lobule on the undersurface of each medially with the uvula of the for its herniation through the foramen cerebellar hemisphere, continuous cerebellar vermis and superiorly with magnum either in congenital or in medially with the uvula of the the flocculonodular lobe. Arterial acquired conditions. Synonyms of the cerebellar vermis and superiorly with branches entering the tonsil originate ‘cerebellar tonsil’ include ‘tonsilla the flocculonodular lobe2. The not only from the posterior but from cerebella’, ‘ventral paraflocculus’, rostromedial margin of the tonsils the anterior inferior cerebellar artery ‘cerebellar amygdala (= almond- borders the tapering edges of the as well, often anastomosing with shaped)’ and ‘amygdala cerebelli’1,2. uvula3. This ovoid structure is attached those from the posterior. The main The tonsil belongs to the posterior to the cerebellum along its

clinical conditions able to affect the cerebellar lobe1. The uvula, the lower superolateral border by a white matter position of the cerebellar tonsil half of the diamond-shaped formation bundle called the tonsillar peduncle. include raised intracranial pressure, of the vermian surface, projects The remaining tonsillar surfaces are myelomeningocele, Chiari downward between the tonsils, thus free surfaces3.

malformations, posterior fossa mimicking the situation in the preparation, read approvedandthe final manuscript. hypoplasia and Idiopathic scoliosis. 3 oropharynx . The inferior (caudal) pole and posterior t The main neurosurgical approaches surface of the cerebellar tonsil face the related to the region of the cerebellar The primary purpose of this review cisterna magna. The lateral surface of tonsil include the was to focus on the gross anatomy, each tonsil is covered by, but is transcerebellomedullary fissure including morphometric separated from the biventral lobule by approach, the tonsillouveal fissure characteristics and arterial a narrow cleft3 (the tonsillobiventral3 approach (telovelar approach), the vasculature, of the human cerebellar or postpyramidal fissure1), except lateral approach to the fourth tonsil. It was also aimed to investigate superiorly at the level of the tonsillar

ventricle, the supra- and subtonsillar the neurosurgical anatomy of this peduncle3. The medial, anterior, and Conflict interests: of Nonedeclared. approaches, the median and far- clinically important structure of the superior surfaces all face other neural lateral suboccipital approaches. human brain. structures, but are separated from them Conclusion by narrow fissures. The position of the cerebellar tonsil The existing literature regarding the can be affected in some congenital and gross and clinical anatomy of the The anterior surface of each tonsil faces acquired disorders including Chiari human cerebellar tonsil was reviewed and is separated from the posterior malformations and raised intracranial with emphasis on its neurosurgical surface of the medulla by the pressure. The high incidence of anatomy. Functional and imaging cerebellomedullary fissure. The medial tonsillar arterial supply of single anatomy data are also presented. surfaces of the tonsils face each other origin, partially explained by vascular Furthermore, neuroanatomical across a narrow cleft, the vallecula comments on the tonsillar cerebelli, which leads into the fourth *Corresponding author morphometry and vasculature are ventricle. The superior (rostral) pole is

Email: [email protected]

All authors contributed All to conception design,and manuscrip All authors All abide by the Association Medical for Ethics (AME) ethical of rules disclosure. provided. separated from the surrounding CompetingNone interests: declared. 1 Department of Neurology, ‘K.A.T.-N.R.C.’ structures by a posterior extension of General Hospital of Attica, Athens, Greece the cerebellomedullary fissure, called

Licensee OAPL (UK) 2014. Creative Commons Attribution License (CC-BY)

FOR CITATION PURPOSES: Mavridis IN. Gross and neurosurgical anatomy of the cerebellar tonsil. OA Anatomy 2014 Apr 09;2(1):8. Page 2 of 6

Critical review

the telovelotonsillar cleft. The hemispheric groups. PICA branches part of the ipsilateral cerebellar tonsil5. superior extension of this cleft over supplying the cortical surface of the The anterior inferior cerebellar artery the superior pole of the tonsil is called tonsil are usually emerging from its (AICA), usually originating from the the supratonsillar cleft3. The ventral lateral trunk (when present)4. The left basilar artery as a single vessel, aspect of the superior pole of each PICA usually courses around the bifurcates into a rostral and a caudal tonsil faces the three structures (tela lower pole of the tonsil while the right trunk5. The caudal trunk often enters choroidea, inferior medullary velum PICA descends well below the tonsil to the lateral portion of the and nodule) forming the lower half of the level of the foramen magnum cerebellomedullary fissure just below the roof of the fourth ventricle. The before ascending along the medial the lateral recess before turning posterior aspect of the superior pole tonsillar surface. The PICAs ascend laterally to supply the inferior part of faces the uvula medially and the between the tonsils and medulla to the petrosal surface. The distal biventral lobule laterally3. reach the interval between the tonsil branches of the caudal trunk often and uvula and to supply the anastomose with the PICA. The AICA The tonsil is the most prominent suboccipital surface3. gives rise to perforating arteries to the structure blocking access to the caudal brainstem, choroidal branches to the part of the fourth ventricle3. The The cortical PICA segment begins lateral segment of the choroid plexus 5 medial segments of the choroid plexus where the trunks and branches leave and nerve-related arteries . of the fourth ventricle stretch from the the groove between the vermis level of the nodule anterior to the medially and the tonsil and the Arterial branches entering the tonsil tonsils to the level of the foramen of hemisphere laterally, and includes the originate not only from PICA but from Magendie. Each medial segment is terminal cortical branches. The AICA as well, often anastomosing with subdivided into a rostral or nodular bifurcation of the PICA, into a medial those from PICA. The number of part and a caudal or tonsillar part. The and lateral trunk, often occurs near cortical branches entering the tonsil tonsillar parts are anterior to the the origin of this segment. The cortical ranges, to the author’s gross anatomical tonsils and extend inferiorly through branches radiate outward from the experience, from two to seven the foramen of Magendie3. superior and lateral borders of the regardless of their origin. The PICA

tonsil to the remainder of the vermis supplies averagely 2.4 (0-7) while AICA The tonsillobiventral fissure is, to the and hemisphere5. The lateral trunk 2.1 (0-7) tonsillar branches. Although author’s anatomical experience, divides into a larger hemispheric PICA dominates the supply of cortical deeper and richer in vessels than the trunk that gives off multiple branches tonsillar branches, AICA seems to

other nearby located sulci. The to the hemisphere and smaller contribute substantially (46.7%) in this maximum tonsillar dimension (24 tonsillar branches that supply the supply. Interestingly, in half of mm) reaches almost the half of the posterior and inferior surfaces of the specimens the cortical tonsillar cerebellar hemisphere’s height (50 tonsil. This division of the lateral branches seem to have a single origin

mm). Tonsillar folia can be either trunk into tonsillar and hemispheric (either PICA or AICA). Vascular

preparation,read and approved the final manuscript.

major or minor and the latter can be branches may occur at various sites in anomalies (such as arterial t occasionally incompletely formed. The relation to the tonsil, but is most hypoplasticity) could only partially mean number of tonsillar sulci is 24 commonly located near the posterior explain this phenomenon. (17-32) and respective number of margin of the medial surface of the major folia is 23 (16-31). tonsil5. Functional data The cerebellum plays an important role Vasculature The tonsillar PICA branches most in coordinating movement. It receives The posterior inferior cerebellar commonly supply the medial, sensory information and influences

artery (PICA), arising from the posterior, inferior and part of the descending motor pathways to produce Conflict interests: of Nonedeclared. vertebral artery, is divided into five anterior surfaces of the tonsil. If there fine, smooth and coordinated motion. segments. The last three are related to are no branches directed The cerebellar tonsil belongs to the cerebellar tonsil: the predominately to the tonsil, the tonsil neocerebellum (also called the tonsillomedullary segment which is supplied by the adjacent pontocerebellum) which is the largest courses around the caudal half of the hemispheric and vermian branches. portion of the cerebellum and cerebellar tonsil; the telovelotonsillar There is a reciprocal relationship with coordinates the movement of the distal segment which courses in the frequent overlap in the areas supplied portions of the limbs. It receives input telovelotonsillar cleft; and the cortical by the tonsillar, hemispheric and from the cerebral cortex and thus helps segment which is distributed to the vermian branches5. The most constant in the planning of 6. cerebellar surface4. The PICA provides cortical areas supplied by the PICA perforating, choroidal and cortical include the anterior aspect of the There are data supporting that the

branches. The cortical branches are tonsil. The smallest area supplied by cerebellar tonsil and other cerebellar

All authors All contributed to conception and design, manuscrip authors All abide by the Association Medical for Ethics (AME) ethical of rules disclosure. divided into vermian, tonsillar and the PICA is confined to the inferior structures, affected in horizontal gaze- CompetingNone interests: declared. evoked nystagmus, are part of a gaze-

Licensee OAPL (UK) 2014. Creative Commons Attribution License (CC-BY)

FOR CITATION PURPOSES: Mavridis IN. Gross and neurosurgical anatomy of the cerebellar tonsil. OA Anatomy 2014 Apr 09;2(1):8. Page 3 of 6

Critical review

holding neural integrator control cases, acute herniation is justifiably Cousins and Haughton18 found 33% system. Furthermore, gaze-evoked considered among the determinant greater average total magnitude of nystagmus might present a diagnostic factors of clinical outcome11. tonsillar motion through the cardiac sign pointing toward ipsilaterally Myelomeningocele, a congenital cycle in patients with Chiari type I located lesions of midline and lower neural tube defect, is associated with malformation (0.57 mm) than in cerebellar structures7. Recent tonsillar herniation and a smaller controls (0.43 mm). Tonsillar motion neuroimaging and neurological data posterior fossa12. was 0.61 mm in patients with implicate cerebellum in non-motor syringomyelia and 0.50 mm in those sensory, cognitive, vegetative and Any inferior displacement of a tonsil without it (22% difference). Suggested affective functions. The cerebellar below the basion-opisthion reference causal mechanisms of tonsillar tonsil, among other cerebellar line in adolescents should be regarded herniation in patients with Chiari type I structures, was found to be activated as abnormal13. Tonsillar ectopia is and type II malformations include by hypercapnia and consequent air defined as any inferior displacement cranial constriction, cranial settling, hunger8. of the tonsils14 or such displacement spinal cord tethering, intracranial with an extent within 5 mm when it is hypertension and intraspinal Imaging data located below the foramen magnum15. hypotension19. Additionally, pre-

Five millimetres sagittal (1.5 Tesla) existing structural abnormalities in the magnetic resonance images (MRIs) of Tonsillar ectopia, encompassing slight posterior fossa may constitute an the cerebellar hemispheres display descent of the cerebellar tonsils and important factor in the development of several structures including the Chiari type I malformation, is tonsillar herniation following tonsils. Surface features of the observed routinely in older children supratentorial shunts20. hemispheres including the deeper and adults and is believed to be an fissures and shallower sulci are best acquired form of the Chiari In idiopathic scoliosis patients the delineated on T1-weighted and T2- malformations. This entity is different position of the tonsil is significantly weighted sequences, which provide from the other Chiari malformations lower and also asymptomatic Chiari greatest contrast between in that hydrocephalus plays no role in type I malformation is frequently cerebrospinal fluid (CSF) and its evolution. More likely it is a reported in these patients13. Tonsillar parenchyma. MRI is useful in disorder of para-axial mesoderm, ectopia with an extent >2 mm in identifying, localising and quantifying characterized by posterior fossa adolescent idiopathic scoliosis patients cerebellar disease in patients with hypoplasia and content overcrowding, should be regarded as abnormal15.

clinical deficits9. and not an embryologic anomaly of These patients have a higher

neuroectoderm16. Tonsillar ectopia is prevalence of tonsillar ectopia than The primary white matter tracts a potentially remediable anomaly controls15. Furthermore, scoliosis could innervating several hemispheric which may first produce symptoms in be an important manifestation of

(including tonsil) and vermian lobules adult life. In these cases diagnosis subclinical tonsillar herniation13.

preparation,read and approved the final manuscript.

are shown well on proton-density- depends on radiological contrast t weighted and T2-weighted spin-echo studies; in particular it is important to Posterior fossa tumours frequently images of 5 mm coronal (1.5 Tesla) examine the cervical canal in prone present with raised intracranial MRIs, which provide excellent and supine positions17. pressure and may cause tonsillar contrast between grey and white herniation. Muzumdar and matter. MRI in the coronal plane The incidence of Chiari type I Ventureyra21 described an uncommon should be especially useful in malformation ranges from less than case of a pilocytic astrocytoma of the identifying, localising, and quantifying 1% to 3%. The occipital and exertional vermis in a 13-year-old girl who

normal and abnormal morphologic headache associated with this presented with clinical features of Conflict interests: of Nonedeclared. differences between the cerebellar malformation can be observed in progressively worsening raised hemispheres10. subjects who have new-onset tonsillar intracranial pressure, secondary ectopia resulting from repeated tonsillar herniation and cervical Neurosurgical anatomy lumbar puncture, idiopathic syringomyelia. The cerebellar tonsils Clinical conditions intracranial hypotension, herniated down to the C2 level and The engagement of cerebellar tonsils lumboperitoneal shunting or there was a centrally located syrinx into the foramen magnum is a well spontaneous development. This new- from C2-T1. The tumour was resected recognised consequence of increased onset headache can remit with return and at follow-up (three months later) intracranial pressure. Tonsillar to normal tonsil positioning. The MRI demonstrated total resolution of herniation is not necessarily a degree of posterior fossa hypoplasia tonsillar herniation and syringomyelia. terminal event, except, in cases in and decrement of CSF flow velocity Further, Fujimoto et al.22 presented a

which it occurs in posterior fossa are important factors determining the case of dysembryoplastic

All authors All contributed to conception and design, manuscrip authors All abide by the Association Medical for Ethics (AME) ethical of rules disclosure. infarcts, acute subdural haematomas, clinical significance of tonsillar neuroepithelial tumours (multiple CompetingNone interests: declared. or during a lumbar puncture. In such ectopia16. cystic lesions on MRI, grey

Licensee OAPL (UK) 2014. Creative Commons Attribution License (CC-BY)

FOR CITATION PURPOSES: Mavridis IN. Gross and neurosurgical anatomy of the cerebellar tonsil. OA Anatomy 2014 Apr 09;2(1):8. Page 4 of 6

Critical review

multinodular gelatinous lesions in ventricle to remove an incidentally to expose the cerebellomedullary pathological examination) in the found arteriovenous malformation of fissure. By dissecting in a subtonsillar cerebellum and brainstem of a 44- the inferior medullary velum. A wide manner around it, the foramen of year-old woman, including the right posterior fossa craniotomy was Luschka can be reached without tonsil. performed to move the cerebellar traversing any neural tissue28. Hosomi et al.23 reported a 66-year-old tonsil laterally with C1 laminectomy. man with small multiple cerebellar The tela chroidea and inferior Lawton et al.29 demonstrated the utility infarcts affecting the tonsil and medullary velum, the two main sheets of the supratonsillar approach, an nodulus (detected by diffusion MRI), of tissue that form the lower half of approach that traverses the who complained of headache, vertigo, the roof of the fourth ventricle can be tonsillobiventral fissure in a trajectory vomiting and chest oppression exposed by gently displacing the over the cerebellar tonsil to the inferior sensation. He could not walk veering tonsils laterally without splitting the cerebellar peduncle, for resecting to right and spontaneous contralateral vermis. Both the cerebellomedullary peduncular cavernous malformations. horizontal nystagmus was noted. and tonsillouveal spaces were It uses wide splitting of the Tsuyuguchi24 also reported a case of exposed. Because the lateral tonsillobiventral fissure. It differs from cerebellar tonsil infarction diagnosed cerebellomedullary cistern was also the transvermian and telovelar

with MRI. Table 1 summarises the exposed, the moving of the cerebellar approaches to the fourth ventricle, with main clinical conditions able to affect tonsil in a lateral direction was easy to a more superolateral trajectory that the position of the cerebellar tonsil. do without injuring the cerebellar leads instead to the inferior cerebellar tissues27. peduncle. By splitting the Surgery tonsillobiventral fissure and mobilizing The tonsillomedullary and During an operation on the caudal the tonsil inferomedially, the point of telovelotonsillar segments of the PICA part of the roof of the fourth ventricle, access to the lesion is deepened and are the most important vessels one should remember that the dentate transgression of normal cerebellar encountered in the nuclei are located just rostral to the tissue is minimised29. transcerebellomedullary fissure superior pole of the tonsils, approach to the fourth ventricle25. underlying the dentate tubercles in Tatagiba et al.30 described the surgical Ucerler et al.25 observed the passing of the posterolateral part of the roof, anatomy of the midline subtonsillar the tonsillomedullary PICA segment where they are wrapped around the approach to the hypoglossal canal. This through the cerebellomedullary superolateral recesses near the lateral approach includes dorsal opening of the

fissure to be placed superior to the edges of the inferior medullary foramen magnum and elevation of the tonsil in 5%, at the level of the upper velum3. ipsilateral cerebellar tonsil to expose pole of the tonsil in 17.5%, at the the hypoglossal nerve and its canal. It middle of the tonsil in 37.5% and at The definitive approach to the permits a straight primary intradural

the level of the lower pole of the tonsil foramen of Luschka is subtonsillar, view to the hypoglossal canal with no preparation,read and approved the final manuscript.

in 37.5% of specimens. A thorough because this foramen is actually the necessity of condylar resections . t understanding of the relationship of end of the natural cleavage plane the PICA branches to the cerebellar between the cerebellar tonsil and Reynier et al.31 reported a patient with tonsils is prerequisite for surgery in medulla28. Jean et al.28 described the a rare peripheral PICA aneurysm and around the fourth ventricle25. operative technique for the located in the tonsillomedullary subtonsillar approach to the foramen segment of the right PICA and formed a The tonsillouveal fissure approach, for of Luschka region. After the cerebellar caudal or infratonsillar loop in the tumours of the fourth ventricle, aims tonsil is freed from arachnoid cisterna magna close to the inferior

to avoid division of the inferior adhesions, it can be retracted part of the tonsil. The operation was Conflict interests: of Nonedeclared. vermis. According to the median rostrodorsally from the medulla, performed with the patient in the inferior suboccipital sitting position using a median cerebellomedullary fissure approach Table 1: Main clinical conditions able suboccipital approach through a C1 (telovelar approach), the trajectory to to affect the position of the cerebellar laminectomy. Interestingly, the authors tonsil the fourth ventricle is made through suggested that aneurysms affecting the the vallecula and microsurgical 1 Raised intracranial pressure (e.g.: telovelotonsillar segment of a PICA, opening of the arachnoidal layers tumours, haematomas, infarcts) forming cranial or supratonsillar loops, allows the separation of the two and those involving its cortical segment tonsils and provides access to the 2 Myelomeningocele can, be effectively operated using the tonsillouveal sulcus, which is located same median suboccipital approach31. between the uvula and nodulus26. 3 Chiari malformations 4 Posterior fossa hypoplasia

All authors All contributed to conception and design, manuscrip authors All abide by the Association Medical for Ethics (AME) ethical of rules disclosure. Shigeno et al. reported the use of the 5 Idiopathic scoliosis CompetingNone interests: declared. lateral approach to the fourth

Licensee OAPL (UK) 2014. Creative Commons Attribution License (CC-BY)

FOR CITATION PURPOSES: Mavridis IN. Gross and neurosurgical anatomy of the cerebellar tonsil. OA Anatomy 2014 Apr 09;2(1):8. Page 5 of 6

Critical review

fashion34. Table 2 summarises the Table 2: Main neurosurgical neurosurgical approaches related to approaches related to the region of the cerebellar tonsil the region of the cerebellar tonsil. 1 Transcerebellomedullary fissure approach Conclusion 2 Tonsillouveal fissureapproach The position of the cerebellar tonsil (telovelar approach) (Figure 1) can be affected in some congenital and acquired disorders

3 Lateral approach to the fourth including Chiari malformations and ventricle raised intracranial pressure. The high

4 Subtonsillar approach incidence of tonsillar arterial supply 5 Supratonsillar approach of single origin, partially explained by vascular anomalies such as arterial 6 Median suboccipital approach hypoplasticity, makes this structure potentially vulnerable to vascular 7 Far-lateral suboccipital approach accidents (mainly infarcts) of the inferior cerebellar arteries. A Słoniewski et al.32 described a case thorough understanding of the involving a ruptured intradural regional tonsillar anatomy, as well as aneurysm of the meningeal branch of its relations with the PICA branches is the occipital artery arising from the of paramount significance for Figure 1: Midsagittal section of brainstem and cerebellum (human brain, left external carotid artery and connecting neurosurgical interventions in this hemisphere). 1: tonsil, 2: roof of the fourth with the caudal loop of the PICA by a area. ventricle, 3: floor of the fourth ventricle, 4: dural fistula. The aneurysm was cerebral aqueduct (of Sylvius), 5: foramen of located intracranially below the tonsil, Abbreviations list Magendie, 6: arbour vitae, 7: pyramid of the

at the site of the connection of the AICA, anterior inferior cerebellar vermis, 8: uvula, 9: nodulus, 10: caudal loop of the PICA with an artery; CSF, cerebrospinal fluid; MRIs, cerebellomedullary fissure, 11: medulla anastomosis of the meningeal branch magnetic resonance images; PICA, oblongata, 12: pons, 13: basilar artery, 14: of the occipital artery, compressing posterior inferior cerebellar artery. midbrain, pyramid, 15: third ventricle 35 the lateral surface of the medulla at (modified from Mavridis ).

the level of the foramen magnum. References They applied a far-lateral suboccipital Icon Custom Communications, pp 72-3, 1. Naidich TP, Duvernoy HM, Delman 2002. approach without removing the arch BN, Sorensen AG, Kollias SS, et al. of the C132. 7. Baier B, Dieterich M. Incidence and

Duvernoy’s atlas of the human brain anatomy of gaze-evoked nystagmus in preparation,read and approved the final manuscript.

stem and cerebellum. Wien: Springer- patients with cerebellar lesions. t Finally, in PICA-PICA bypass, the PICA Verlag, pp 20-21, 2009. is isolated in its lateral medullary or Neurology. 2011 Jan;76(4):361-5. 2. Wikipedia, the free encyclopedia. 8. Parsons LM, Egan G, Liotti M, tonsillar loop and dissected free of Tonsil. Available from: arachnoid. The technique of Brannan S, Denton D, Shade R, et al. http:en.wikipedia.org/wiki/Cerebellar Neuroimaging evidence implicating anastomosis is similar to that of the _tonsil; 2013 [accessed 18 May 2013]. superior temporal artery-middle cerebellum in the experience of 3. Rhoton AL Jr. Cerebellum and hypercapnia and hunger for air. Proc cerebral artery bypass. If the AICA is fourth ventricle. Neurosurgery. 2000 the recipient vessel, the lateral branch Natl Acad Sci U S A. 2001 Sep;47(3 Suppl):S7-27. Conflict interests: of Nonedeclared. of the AICA posterior to the VIIIth Feb;98(4):2041-6. 4. Lister JR, Rhoton AL Jr, Matsushima 9. Press GA, Murakami J, Courchesne E, cranial nerve is isolated and used for T, Peace DA. Microsurgical anatomy of the anastomosis33. Berthoty DP, Grafe M, Wiley CA, et al. the posterior inferior cerebellar The cerebellum in sagittal plane- artery. Neurosurgery. 1982 Quiñones-Hinojosa et al.34 reported a anatomic-MR correlation: 2. The Feb;10(2):170-99. cerebellar hemispheres. AJR Am J 30-year-old man with subarachnoid 5. Rhoton AL Jr. The cerebellar haemorrhage due to a right vertebral Roentgenol. 1989 Oct;153(4):837-46. arteries. Neurosurgery. 2000 Sep;47(3 10. Press GA, Murakami JW, Courchesne artery dissecting aneurysm. The Suppl):S29-68. patient underwent a suboccipital E, Grafe M, Hesselink JR. The 6. Netter FH, Craig JA, Perkins J, cerebellum: 3. Anatomic-MR craniotomy, where the PICAs were Hansen JT, Koeppen BM. Atlas of brought together between the tonsils correlation in the coronal plane. AJNR Neuroanatomy and Neurophysiology: Am J Neuroradiol. 1990 Jan- with a side-to-side anastomosis to Selections from the Netter Collection

allow the contralateral PICA to supply Feb;11(1):41-50.

All authors All contributed to conception and design, manuscrip authors All abide by the Association Medical for Ethics (AME) ethical of rules disclosure. of Medical Illustrations. Teterboro NJ: CompetingNone interests: declared. the ipsilateral PICA in a retrograde

Licensee OAPL (UK) 2014. Creative Commons Attribution License (CC-BY)

FOR CITATION PURPOSES: Mavridis IN. Gross and neurosurgical anatomy of the cerebellar tonsil. OA Anatomy 2014 Apr 09;2(1):8. Page 6 of 6

Critical review

11. Simonetti F, Pergami P, Ceroni M, posterior fossa tumors in children: a 31. Reynier Y, Alliez B, Diaz A. [Distal Ropper AH, Viviani R. About the case-based update. Childs Nerv Syst. aneurysm of the postero-inferior original description of cerebellar 2006 May;22(5):454-9. cerebellar artery. Anatomical and tonsil herniation by Pierre Marie. J 22. Hosomi A, Yamamoto Y, Hamanaka surgical considerations]. Neurol Neurosurg Psychiatry. 1997 M, Nakagawa M. [A patient with small Neurochirurgie. 1992;38(6):358-61. Sep;63(3):412. cerebellar infarcts at tonsil and French. 12. Grant RA, Heuer GG, Carrión GM, nodulus who complained of vertigo, 32. Słoniewski P, Dzierzanowski J, Och Adzick NS, Schwartz ES, Stein SC, et al. vomiting and chest oppression]. W. Aneurysm of the meningeal branch Morphometric analysis of posterior Rinsho Shinkeigaku. 2007 of the occipital artery connecting with fossa after in utero myelomeningocele Aug;47(8):522-5. Japanese. the distal portion of the posteroinferior repair. J Neurosurg Pediatr. 2011 23. Fujimoto K, Ohnishi H, Tsujimoto cerebellar artery by the dural fistula. Apr;7(4):362-8. M, Hoshida T, Nakazato Y. Folia Morphol (Warsz). 2008 13. Cheng JC, Chau WW, Guo X, Chan Dysembryoplastic neuroepithelial Nov;67(4):292-5. YL. Redefining the magnetic tumor of the cerebellum and 33. Sekhar LN, Natarajan SK, resonance imaging reference level for brainstem. Case report. J Neurosurg. Ellenbogen RG, Ghodke B. Cerebral the cerebellar tonsil: a study of 170 2000 Sep;93(3):487-9. revascularization for ischemia,

adolescents with normal versus 24. Tsuyuguchi N. [A case of cerebellar aneurysms, and cranial base tumors. idiopathic scoliosis. Spine (Phila Pa tonsil infarction diagnosed with MR Neurosurgery. 2008 Jun;62(6 Suppl 1976). 2003 Apr;28(8):815-8. imaging]. No To Shinkei. 2001 3):1373-408;discussion 1408-10. 14. Chen ZJ, Qiu Y, Sun X, Ma WW. Sep;53(9):886-7. Japanese. 34. Quiñones-Hinojosa A, Lawton MT. [Study of relationship between 25. Ucerler H, Saylam C, Cagli S, Orhan In situ bypass in the management of position of the cerebellar tonsil and M, Zileli M. The posterior inferior complex intracranial aneurysms: abnormal somatosensory evoked cerebellar artery and its branches in technique application in 13 patients. potentials in adolescent idiopathic relation to the cerebellomedullary Neurosurgery. 2005 Jul;57(1 scoliosis]. Zhonghua Wai Ke Za Zhi. fissure. Clin Anat. 2008 Suppl):140-5;discussion 140-5. 2009 Jun;47(11):829-32. Chinese. Mar;21(2):119-26. 35. Mavridis IN. [Stereotactic

15. Sun X, Qiu Y, Zhu Z, Zhu F, Wang B, 26. Yaşargil MG, Abdulrauf SI. Surgery neurosurgical anatomy of the nucleus Yu Y, et al. Variations of the position of of intraventricular tumors. accumbens]. PhD Thesis, National and the cerebellar tonsil in idiopathic Neurosurgery. 2008 Jun;62(6 Suppl Kapodistrian University of Athens scoliotic adolescents with a cobb angle 3):1029-40;discussion 1040-1. (School of Medicine), Athens, Greece,

>40 degrees: a magnetic resonance 27. Shigeno T, Kumai J, Endo M, Hotta 2012, p 22. Greek. imaging study. Spine (Phila Pa 1976). S. [Surgery of AVM of the inferior 2007 Jul;32(15):1680-6. medullary velum by the uvulotonsillar 16. Arnett BC. Tonsillar ectopia and approach--advantage of moving of the

headaches. Neurol Clin. 2004 cerebellar tonsil: technical case

preparation,read and approved the final manuscript.

Feb;22(1):229-36. report]. No Shinkei Geka. 2002 t 17. Smith J, Ridley A. Cerebellar Jan;30(1):87-92. Japanese. ectopia presenting in adult life. Br 28. Jean WC, Abdel Aziz KM, Keller JT, Med J. 1969 Feb;1(5640):353-5. van Loveren HR. Subtonsillar 18. Cousins J, Haughton V. Motion of approach to the foramen of Luschka: the cerebellar tonsils in the foramen an anatomic and clinical study. magnum during the cardiac cycle. Neurosurgery. 2003 Apr;52(4):860- AJNR Am J Neuroradiol. 2009 6;discussion 866.

Sep;30(8):1587-8. 29. Lawton MT, Quiñones-Hinojosa A, Conflict interests: of Nonedeclared. 19. Milhorat TH, Nishikawa M, Kula Jun P. The supratonsillar approach to RW, Dlugacz YD. Mechanisms of the inferior cerebellar peduncle: cerebellar tonsil herniation in patients anatomy, surgical technique, and with Chiari malformations as guide to clinical application to cavernous clinical management. Acta Neurochir malformations. Neurosurgery. 2006 (Wien). 2010 Jul;152(7):1117-27. Oct;59(4 Suppl 2):ONS244- 20. Lazareff JA, Kelly J, Saito M. 51;discussion ONS251-2. Herniation of cerebellar tonsils 30. Tatagiba M, Koerbel A, Roser F. following supratentorial shunt The midline suboccipital subtonsillar placement. Childs Nerv Syst. 1998 approach to the hypoglossal canal: Aug;14(8):394-7. surgical anatomy and clinical

21. Muzumdar D, Ventureyra EC. application. Acta Neurochir (Wien).

All authors All contributed to conception and design, manuscrip authors All abide by the Association Medical for Ethics (AME) ethical of rules disclosure. Tonsillar herniation and cervical 2006 Sep;148(9):965-9. CompetingNone interests: declared. syringomyelia in association with

Licensee OAPL (UK) 2014. Creative Commons Attribution License (CC-BY)

FOR CITATION PURPOSES: Mavridis IN. Gross and neurosurgical anatomy of the cerebellar tonsil. OA Anatomy 2014 Apr 09;2(1):8.