Morphometric Analysis of Tentorial Incisura and its Clinical Implications

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1 Originl Article Print ISSN: Online ISSN: X DOI: /ijss/2017/504 Morphometric Anlysis of Tentoril Incisur nd its Clinicl Implictions K Rjrjn 1, R Prgdhees 1, SS Sthish Prbu 2, S Prdeep 2 1 Assistnt Professor, Deprtment of Neurosurgery, Mduri Medicl College & Government Rjji Hospitl, Mduri, Tmil Ndu, Indi, 2 Resident, Deprtment of Neurosurgery, Mduri Medicl College & Government Rjji Hospitl, Mduri, Tmil Ndu, Indi Abstrct Introduction: Tentoril incisur is importnt due to trnstentoril hernition, terminl pthophysiologicl event in vrious neurosurgicl conditions. With dvent of modern neurordiologicl methods lcun in understnding of hernition syndromes is being grdully filled. Aim: To nlyze ntomicl vrition, clssy types nd their clinicl relevnce nd interprettion on neurordiologicl imging. Mterils nd Methods: Totl 100 mgnetic resonnce imges (MRI) of brin were nlyzed using RdiAnt DiCom viewer. Sttisticl methods used descriptive nlysis, Person correltion, significnt two-tiled test, student t-test, nd nlysis of vrince. Results: Notch length is typed into three, mximum notch width into three. By combintion, the tentoril incisur is typed into nine types. Correltion between prmeters nd sttisticl significnce is interpreted. Conclusion: Morphometry clssifiction nd reltive smller dimensions of ntomicl structures nd reltionships in Indin popultion hve been elucidted. Vrious mnifesttions of hernition syndromes explined. Pre-opertive MRI morphometric nlysis hs been highlighted. Key words: Mgnetic resonnce imges, Morphometric nlysis, Tentoril incisur INTRODUCTION The tentoril incisur is n ntomicl structure tht crries with it tremendous clinicl nd pthologicl importnce in the field of neurosurgery. The incisur is surrounded by myrid of vitl structures tht mndtes exercising utmost cution during the course of the performnce of vrious complicted neurosurgicl procedures in tht region. The phenomenon of trnstentoril hernition tht ws first described by Meyer 1 in the yer 1920 is terminl pthophysiologicl occurrence in vrious neurosurgicl conditions rnging from trumtic brin injury to brin tumor progression. 2 However, for wnt of dvncement in modern neurordiologicl imging techniques, there Access this rticle online Month of Submission : Month of Peer Review : Month of Acceptnce : Month of Publishing : remined lcun in our understnding of Hernition syndromes. 3 With the dvent of modern imging methods, this void is being grdully filled by our ever-growing understnding of the neurontomicl spects of the tentoril incisur. 4 The tentoril incisur hs numerous ntomicl vritions which contribute to nd influence the rpidity of onset nd progression of hernition irrespective of the underlying cuse. Numerous morphometric studies hve been conducted on vrious spects of the brin, however, studies regrding the ntomicl vritions of the tentoril incisur re very limited, nd the vilble studies hve been conducted in cdvers in the sixties. 5,6 In this study, norml ntomicl vritions in the dimensions of the tentoril notch nd position of the brinstem in reltion to the tentoril hitus re mesured nd nlyzed using currently vilble mgnetic resonnce imging (MRI) techniques. These fctors re likely to hve immense bering on the progression nd outcome of trumtic brin injury nd other neurosurgicl cuses of hernition syndromes. These lso crry implictions during Corresponding Author: Dr. R Prgdhees, Deprtment of Neurosurgery, Government Rjji Hospitl, Mduri, Tmil Ndu, Indi. Phone: E-mil: prgdhees_r@yhoo.com Interntionl Journl of Scientific Study October 2017 Vol 5 Issue 7 98

2 micro neurosurgicl pproches while ttempting to del with lesions in the vicinity of the hitus. The tentoril hitus is complex void tht vries gretly in size nd shpe mong individuls. Although it cn be simply described s the free edge of the tentorium cerebelli, it is much more complex thn wht meets the eye. The reson behind this complexity is primrily its three-dimensionl ntomy with lck of blood vessels in its edges nd occurrence of occsionl clcifiction. Hence, visuliztion nd quntifiction of this structure remined chllenge for neurosurgeons nd neurontomists for decdes. With the dvent of modern imging modlities, this elusive process hs become more within rech nd thus enhncing our knowledge of this structure. In-depth understnding nd chrcteriztion of the hitus nd induction of prcticl nd simple clssifiction of it my help explin ptterns of hernitions, susceptibility of the oculomotor nerve to compression nd pthomechnics of concussion nd inertil injuries of the brin. With the entry of powerful operting microscopes into the field of neurosurgery, new er hs been ushered into this field which hs mde erlier impossible nd untouchble lesions of the brin within the rech of the neurosurgeon with miniml retrction of the norml brin nd t times with negtion of the very need for touching the norml brin prenchym. By doing so, the risk nd complictions ssocited with crnil surgery cn be gretly minimized nd ltogether voided t times. or non-centrl nervous system pthology, either s n inptient or s n out-ptient. Hence, ny ptient who during the process of imging ws found to hrbor n intrcrnil pthology such s n intrcrnil spce-occupying lesion ws excluded from the study. Method Used MRI in xil, sgittl nd coronl sections were selected nd nlyzed using RdiAnt DiCom Viewer which is verstile open source softwre vilble for common usge. Prmeters mesurement (Figures 1-4) in millimeters. 1. Anterior notch width (ANW): The width of the tentoril hitus in the xil plne mesured through the posterior spect of dorsum selle 2. Mximum notch width (MNW): Mximum width of the notch in the xil plne 3. Notch length (NL): Distnce between superoposterior edge of Dorsum Selle in medin plne to the pex of the notch 4. Posterior tentoril length (PTL): Shortest distnce between the pex of the notch nd the confluence of sinuses 5. Apico tectl distnce (AT): Distnce from the tectum in the medin plne to perpendiculr line dropped from the pex of the notch to the cerebellum 6. Inter-pedunculoclivl distnce (IC): Distnce between Morphometric dt llows for precise nd foolproof preopertive plnning of loction of the lesion nd trjectory towrd the lesion which provides the lest trnsgression of norml tissue. This is of prmount importnce in reducing opertive morbidity nd much dreded but frught mortlity ssocited with neurosurgery since time immemoril. Aim of the Study 1. To nlyze the ntomicl vritions of the tentoril incisur 7 2. To clssify the vrious types of tentoril incisur 3. To elucidte the clinicl relevnce of these vritions 4. To estblish n ntomicl bsis for interprettion of the tentoril hitus on rdiologicl imging. Figure 1: ( nd b) Tentoril incisur b MATERIALS AND METHODS Study Group Our study group consisted of 100 ptients ged between 18 nd 60 yers undergoing MRI of the brin per se in the bsence of orgnic lesions of the brin or s prt of the screening of the brin in cses of spinl pthology Figure 2: Tentoril incisur mesurements 99 Interntionl Journl of Scientific Study October 2017 Vol 5 Issue 7

3 the interpedunculr foss to the superoposterior edge of the Dorsum Selle 7. Cephlic index (CI): (Clvril bredth/nteroposterior clvril length) 100. Sttisticl Methods In this study, the following sttisticl methods were utilized. They re: 1. Descriptive nlysis 2. Person correltion 3. Significnt two-tiled test 4. Student t-test 5. Anlysis of vrince. OBSERVATIONS AND RESULTS In our study, totl of 100 ptients were nlyzed tking mesurements t vrious pre-defined levels. The rw dt were tbulted. Descriptive Anlysis (Tble 1) Correltion (Tble 2) To scertin the correltion between the vrious dt sets we used the Person Correltion technique (r vlue) nd obtined the corresponding P-vlue using significnt twotiled test. The following sttisticlly significnt correltions were observed. There ws significnt (P < 0.05) positive correltion between ANW nd MNW, MNW nd NL, AT nd IC, AT nd AP, AT nd BR, PTL nd BR. There ws significnt negtive correltion (P = <0.05) between ANW nd AT. There ws highly significnt correltion (P < 0.01) between MNW nd IC, NL nd AT, NL nd IC, NL nd AP, NL nd BR, NL nd AT, PTL nd Anteroposterior length of skull. Age ws not sttisticlly correlted with ny of the Dimensions mesured. Student t-test (Tbles 3 nd 4) ANOVA Anlysis of vrince with ge s dependent vrible showed tht ANW (P = 0.003) nd MNW (P = 0.002). None of the fctors hd sttisticlly significnt dependence on ge. Tking into considertion ll the bove sttisticl methods, the dimensions of the tentoril hitus re clssified s follows. NL is short <48.7 mm (n = 24), midrnge mm (n = 51), nd long >55.1 mm (n = 25). MNW is nrrow <27.6 mm (n = 22), midrnge mm (n = 54), nd wide >31.2 mm (n = 24). Mtrix distribution ws done to clssify the Tentoril Hitus (Tble 5 nd Figure 5). Clssifiction of Tentoril Notch (Tble 6) In our study, totl of 100 ptients were nlyzed tking mesurements t vrious pre-defined levels. The rw dt c b Figure 3: Mesurements in MRI Tble 1: Descriptive nlysis Method Age ANW MNW NL AT IC PTL AP BR CI Vlid Missing Men Stndrd error of men Medin Mode Stndrd devition Vrince Rnge Minimum Mximum Percentiles Percentiles Percentiles Multiple modes exist. The smllest vlue is shown, MNW: Mximum notch width, NL: Notch length, PTL: Posterior tentoril length, ANW: Anterior notch width, AT: Apico tectl, CI: Cephlic index Interntionl Journl of Scientific Study October 2017 Vol 5 Issue 7 100

4 Tble 2: Person correltion nd significnt two-tiled test ANW MNW PC 0.239* Sig MNW NL PC * Sig NL AT PC 0.207* ** Sig AT IC PC ** 0.392** 0.237* Sig IC PTL PC Sig PTL AP PC ** 0.241* ** Sig AP BR PC ** 0.234* * 0.299** Sig BR CI PC ** 0.390** Sig CI AGE PC * Sig PC: Person correltion, *Correltion is significnt t the 0.05 level (two tiled), **Correltion is significnt t the 0.01 level (two tiled), Sig: Significnt two tiled test, MNW: Mximum notch width, NL: Notch length, PTL: Posterior tentoril length, ANW: Anterior notch width, AT: Apico tectl, CI: Cephlic index Tble 3: 95% confidence intervl of the difference Prmeter Lower Upper ANW MNW NL AT IC PTL AP BR CI MNW: Mximum notch width, NL: Notch length, PTL: Posterior tentoril length, ANW: Anterior notch width, AT: Apico tectl, CI: Cephlic index d b e Figure 4: Tentoril incisur. () mid mximum notch width (MNW) nd long notch length (NL), (b) mid MNW nd mid NL, (c) mid MNW nd short NL, (d) wide MNW nd mid NL, (e) mid MNW nd long NL c Tble 4: ANOVA Prmeter Sum of squre df Men squre F Significnt ANW B/G W/G Totl MNW B/G W/G Totl NL B/G W/G Totl AT B/G W/G Totl IC B/G W/G Totl PTL B/G W/G Totl AP B/G W/G Totl BR B/G W/G Totl CI B/G W/G Totl MNW: Mximum notch width, NL: Notch length, PTL: Posterior tentoril length, ANW: Anterior notch width, AT: Apico tectl, CI: Cephlic index 101 Interntionl Journl of Scientific Study October 2017 Vol 5 Issue 7

5 Tble 5: Clssifiction of tentoril notch Clssifiction NL n=100 Short Midrnge Long MNW Nrrow Smll (9) Nrrow (10) Mixed (3) Midrnge Short (11) Typicl (29) Long (14) Wide Mixed (4) Wide (12) Lrge (8) MNW: Mximum notch width, NL: Notch length Tble 6: Clssifiction of tentoril notch Clssifiction Wide notch MNW (wide) NL (mid) Nrrow notch MNW (nrrow) NL (mid) Long notch MNW (mid) NL (long) Short notch MNW (mid) NL (short) Typicl notch MNW (mid) NL (mid) Lrge notch MNW (wide) NL (long) Smll notch MNW (nrrow) NL (short) Mixed notch 1 MNW (wide) NL (short) Mixed notch 2 MNW (nrrow) NL (long) MNW: Mximum notch width, NL: Notch length reptiles, nd mphibious nimls. In nother subset, the tent is incomplete in the sense tht it does not rech the midline t ll, such s morphology is seen in guine pigs nd rodents. Only in higher mmmls such s humns nd primtes, the tent forms thick membrne prtitioning the superiorly locted cerebrl hemispheres nd the inferiorly locted cerebellr hemispheres. The opening of the tentorium, nmely, the tentoril Hitus or notch or incisur, surrounds the midbrin structures. When studies on the phylogeny nd development of the tent were conducted, it ws inferred tht this is structure tht emerged lter during eons of evolution. It ws first found s symmetricl durl folds on either side of the midbrin in the cerebro-cerebellr fissure. As time went by, the flx cerebri descended down to meet the tentorium t more nd more points, crrying with it the formtion of stright sinus. As species evolved, the length of the stright sinus incresed nd so did the dimensions of the hitus. Similr studies in Indin popultion re few nd fr between. Even western studies of the sme hve been conducted in cdveric smples. Live in vivo studies re limited if not lmost non-existent. It is generlly ccepted fct tht the morphologicl fetures of the popultion of the west correlte poorly with tht of the Asin popultion. Western individuls hve much lrger hed with greter CI with lrger structurl fetures compred to people of the Est, especilly the Indin nd other Asin popultion. were tbulted. Tentoril incisur cn be brodly clssified into nine ntomicl vritions. DISCUSSION Figure 5: Types of tentoril incisur As erly s the yer 1958, before the dvncement of mgnetic resonnce nd other imging technology, Sunderlnd nd collegues ctegorized the tentoril notch into two types - brod nd nrrow. 6 In the sme line, Adler nd Milhort clssified it into eight types bsed on cdveric studies. 8 Klintworth et l. put forth the concept tht the tentorium nd its opening re highly vrible in respect to their size, shpe, dimensions, nd orienttion in vrious niml species. 9 There re even few nimls in the world in which such structure is clssiclly bsent. These include fishes, During the process of brin hernition due to vrious cuses, there occurs gross ntomicl distortion of tissue s they come down through the tentoril perture. This produces highly loclizing signs nd clinicl fetures in the ptient. The fetures found in pthologicl specimen include. 1. Medil displcement of the temporl lobe or the prt in question 2. Medil displcement of the brinstem structures 3. Grooving of the brinstem 4. Descent of the hippocmpl gyrus 5. Compression of the ipsilterl oculomotor nerve 6. Chrcteristic Duret hemorrhges into the brinstem. Although the bove-enlisted fetures re generliztion of the incidence occurring during hernition, these re not ll found in the sme ptient or mong different ptients undergoing this moribund potentilly ftl pthologicl process. The reson for this difference in mnifesttions of the sme process in different individuls is uncler. Interntionl Journl of Scientific Study October 2017 Vol 5 Issue 7 102

6 This lso fils to explin the incidentl occurrence of the neurosurgiclly fmed flse loclizing signs. All the bove prdoxes cn be explined due to the ntomicl vritions in the tentoril notch in individuls of the sme species, in our cse humn beings. It hs been proven tht longer nd wider incisur hve greter mount of cerebellr tissue exposed when compred to those tht re nrrow nd shorter. Smll pertures logiclly expose lesser mount of brin tissue. This exposure vribility in reltion to the dimensions of the notch hs vible implictions in regrd to the propensity of occurrence of hernition syndromes, be it descending or scending hernitions. During the postmortem exmintion of the humn brin, it is customry to obtin the specimen by the division of the flx cerebri nd the tentorium, so s to enble mobiliztion nd delivery of the brin. 10 This invribly cuses unvoidble distortion of the norml ntomy. This compounds the lredy present chnges inherent to ded brin specimen. This ntomicl distortion cn be circumvented by studying the brin in its nturl live stte in humns using the now freely vilble MRI techniques. It is much esier to see the ntomicl lndmrks nd to mke ccurte in situ mesurements of the vrious dimensions of interest without cusing undue morbidity to the ptient. However, the only limiting fctor in country like ours is the vilbility of MRI equipment, the running costs involved, the time consumption for imge cquisition nd the ptient-borne cost fctor. All the prmeters looked for by the uthors of vrious cdveric studies cn be sought nd esily quntified. Bsed on these, the position of the brinstem nd type of incisur cn be identified. This mesurement cn lso be used to clculte nd pln the trjectory during neurosurgicl opertions in the brin especilly in lesions in nd round the tentoril hitus. Such proper plnning cn void unnecessry morbidity nd even mortlity during performing complicted microneurosurgicl procedures. 11,12 CONCLUSION The following conclusions cn be drwn from this study. A morphometry bsed clssifiction of the tentoril hitus hs been formulted. Vrious dimensions of the region of the tent hve been mesured in representtive subset of South Indin popultion. Antomicl mke up of our popultion with tht of the popultion represented in Western studies re compred. Reltively smller dimensions of ntomic structures nd reltions in Indin popultion hve been elucidted. The reson for vrible mnifesttions of hernition syndromes cn be explined. In this study, ANW correltes positively with MNW. MNW correltes positively with NL. AT distnce, NL nd interpedunculr-clivl distnce re significntly correlted. There is no significnt correltion between ge, CI nd the hitus dimensions. The vlue of rdiology bsed morphometric nlysis in pre-opertive neurosurgicl plnning hs been highlighted. ACKNOWLEDGMENT We thnk with grtitude Professor Dr. S. Revwthy Kilirjn. M.D., D.G.O.DNB, Former Den nd Professor Dr. M.R. Virmuthurj. M.D, Former Den, Government Rjji Hospitl nd Mduri Medicl College, Mduri, for permitting us to utilize the clinicl mterils of this hospitl. We re grtefully indebted to Professor Dr. N. Muthukumr. M.Ch, Deprtment of Neurosurgery, for the invluble guidnce nd dvice rendered in the study. We lso sincerely cknowledge the guidnce nd support given by Professor Dr. R. Veerpndin. M.S., M.Ch nd Professor Dr. J. Srisrvnn. M.S., M.Ch in enbling us to go through nd complete this study. We sincerely cknowledge Professor Dr. Sumthi. M.D., DMRD, Hed of the Deprtment of Rdiology, for permitting us to utilize the resources of her deprtment. We lso immensely thnkful to ll the Assistnt Professors of the Deprtment of Neurosurgery, for their guidnce in completion of the study. We lso express our hertfelt grtitude to the technicl stff of the Deprtment of Rdiology, for their support nd helping hnd in the conduct of the study. We lso express our grtitude to Mr. S. Pndi. M.Sc., Assistnt Professor of Sttistics, Mduri Medicl College, for his invluble help towrd completion of the study. REFERENCES 1. Meyer A. Hernition of the brin. Arch Neurol Psychitry 1920;4: Munro D, Sisson WR Jr. The recognition nd tretment of incisures hernition cused by crniocerebrl injuries. Trns Am Neurol Assoc 1950;75: Ardeshiri A, Ardeshiri A, Wenger E, Holtmnnspötter M, Winkler PA. Surgery of the nterior prt of the frontl lobe ndofthe centrl region: Normtive orphometric dt bsed on mgnetic resonnce imging. Neurosurg Rev 2006;29: Bky L, Lee JC, Lee GC, Peng JR. Experimentl cerebrl concussion. Prt 1: An electron microscopic study. J Neurosurg 1977;47: Corsellis JA. Individul vrition in the size of the tentoril opening. J Neurol Neurosurg Psychitry 1958;21: Sunderlnd S. The tentoril notch nd complictions produced by hernitions of the brin through tht perture. Br J Surg 1958;45: Windle WF, Grot RA, Fox CA. Experimentl structurl ltertions in the brin during nd fter concussion. Surg Gynecol Obstet 1944;79: Interntionl Journl of Scientific Study October 2017 Vol 5 Issue 7

7 8. Adler DE, Milhort T. The tentoril notch: Antomicl vrition, morphometric nlysis, nd clssifiction in 100 humn utopsy. J Neurosurg 2002;96: Klintworth GK. The ontogeny nd growth of the humn tentorium cerebelli. Ant Rec 1968;160: Bull JW. Tentorium cerebelli. Proc R Soc Med 1969;62: Nguyen JP, Djindjin M, Brugières P, Bdine S, Melon E, Poirier J. Antomy-computerized tomogrphy correltions in trnstentoril brin hernition. J Neurordiol 1989;16: Reich JB, Sierr J, Cmp W. Mgnetic resonnce imging mesurements nd clinicl chnges ccompnying trns tentoril nd formen mgnum brin hernition. Ann Neurol 1993; How to cite this rticle: Rjrjn K, Prgdhees R, Prbu SSS, Prdeep S. Morphometric Anlysis of Tentoril Incisur nd its Clinicl Implictions. Int J Sci Stud 2017;5(7): Source of Support: Nil, Conflict of Interest: None declred. Interntionl Journl of Scientific Study October 2017 Vol 5 Issue 7 104