meningoceles' and 'meningomyeloceles' (ectopic spinal · 2008. 11. 5. · j. neurol....

J. Neurol. Neurosurg. Psychiat., 1970, 33, 251-262

'Meningoceles' and 'meningomyeloceles'(ectopic spinal cord)

Clinicopathological basis of a new classification

VASANT C. TALWALKER AND DARAB K. DASTUR

From the Neuropathology Unit, Postgraduate Research Laboratories, J.J Group of Hospitals,Bombay-8, India

While the terms 'meningocele' and meningomyelo-cele', as defined in a dictionary, appear clearlyseparate, these words have been qualified andassigned nuances by a variety of workers, renderingthem somewhat confusing today. Thus for instance,a dictionary (Dorland, 1965) defines a meningomyelo-cele as 'a hernial protrusion of a part of themeninges and substance of the spinal cord througha defect in the vertebral column'. This, however,appears to be an over-simplification, since in mostcases the lesion of the spinal cord is more than asimple herniation into a sac. In fact, as shown byCameron (1956) in his comprehensive investigation,the initial malformation in all cases of 'meningo-myelocele' was an open myelocele which tended tobe covered in time by an epithelialized scar. Theclassification of the congenital lesions of the spineand cord, associated with a spina bifida, proposedby Cameron and endorsed by Willis (1962) andothers (for example, Greenfield, 1963), is as follows:

l. Spina bifida occulta, where the cord remainsinside the canal.

2. Meningocele, where a cystic swelling isformed by dura and arachnoid and the cord re-mains in the canal.

3. Meningomyelocele, where the cord is closelyapplied to the fundus of a cystic swelling.

4. Myelocele, where part of the spinal cord isexposed to the surface. Willis also uses the term'local myeloschisis' for the last category of Cameron,and further includes a fifth category of 'totalmyeloschisis' where almost the whole of the spinalcanal is open. Both Cameron and Willis have thusmade it clear that most if not all meningomyelo-celes are epithelialized myeloceles. McMenemey(1967) uses the term 'rachischisis' in place of myelo-schisis,whileessentially adhering to this classification.

The present communication attempts a newclassification of what have hitherto been describedas 'meningoceles' and 'meningomyeloceles', onthe basis of our clinicopathological observationsof the last four years. It was apparent to us that thepresence or absence of involvement of the cord andthe roots constituted the basis of the anatomicallesion, the neurological deficit, and the nature ofany surgical intervention. The two main lesionsthat impressed us were a tethering of the lower endof the spinal cord in some cases of meningocelesand 'meningomyeloceles', and the gross exposureof the spinal cord, best described as an ectopia,which is the hall-mark of the 'meningomyelocele'.It is also suggested that the latter term be droppedaltogether in favour of the term meningocele withectopic spinal cord. These two varieties of congenitalanomaly of the spinal canal, meninges, and the cord,along with other similar anomalies, will be includedin the proposed new classification of meningoceles.

MATERIAL AND METHODS

Fifty-one consecutive cases of spinal meningocelesof all types operated on by one of us (V.C.T.) constitutethe present material. The neuropathologist (D.K.D.)assisted at many of these operations. Included in thematerial are two post-mortem specimens, which wereavailable for complete dissection, one of a full-termbaby with ectopic and tethered spinal cord, and theother of a 6 month foetus with total ectopia of thespinal cord (total myeloschisis), who alEo had inience-phaly and a completely exposed brain.

SURGICAL METHODS All babies with ectopic spinalcord were operated upon as soon after birth as possible;many babies with meningoceles were also operatedon soon after birth. In the babies with ectopic spinalcord the operation consisted simply of providing a

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Vasant C. Talwalker and Darab K. Dastur

skin cover to the exposed cord under local anaesthesia.No tissue was excised. The thin membrane attached tothe spinal cord was buried along with it. No attemptwas made to close the dura over the spinal cord. Skinand subcutaneous tissue were stitched in two layers,using the thick ridge of subcutaneous tissue which isusually present in these babies at the periphery of thedefect. Whenever the cord was found tethered to thesacral vertebrae, it was released by dividing the tetheringband as far down from the lower end of the cord aspossible.

In the cases of meningocele without ectopic spinalcord, whenever the defect in the bony spines was smallthere was no opportunity to inspect the inner side ofthe spinal canal and the meningocele was excised atits neck flush with the posterior spines. However, whenthe defect in the spine was wide, it permitted inspectionof the spinal canal and the dura was opened to findout the nature of the anomaly of the spinal cord androots. Whenever the spinal cord or roots were foundadherent to the stalk or the base of the mass, the stalkwas divided a little distance above the level of thenervous tissue. The part of the stalk bearing this tissuewas gently pushed back into the canal and the dura materand the skin closed over it in layers.

Further details of the operative findings will bepresented in the description of the different subgroups.

PATHOLOGICAL METHODS The biopsy specimens werefixed in formalin and blocked in paraffin. The sectionswere stained with haematoxylin and eosin for cellulardetails and with the Picro-Mallory method for connectivetissues. Occasionally phosphotungstic-acid haematoxylinstaining for glial elements and Kluver-Barrera's methodfor nerve cells and myelin were employed. When eosino-philic or amphophilic material was found accumulatedin masses or in cells, periodic-acid-Schiff stain, Krajian'smethod for mucin and/or amidoblack for protein, wereused. Similar procedures for fixation, embedding, andstaining were carried out on necropsy material also.The entire foetuses were fixed in formalin in the twoinstances where they were available. The exposed oraffected spinal cord was sectioned at all levels.

OBSERVATIONS

The fifty-one cases could be grouped into twomain categories and into nine sub-categoriesaccording to the anatomical lesion. The two maincategories were based on the absence or presenceof an ectopic spinal cord. The second group wascharacterised by ectopia together with extensiveand wide posterior spina bifida and correspondingdeficiencies of the posterior spinal meninges andskin. Clinically, such cases manifested significantneurological deficit, generally paralysis of thelegs and of the sphincters, soon after birth. Incontrast, the first group was characterized by thespinal cord remaining within the dural sac and

spinal canal, with or without a tethering of thelower end of cord or roots. The clinical presentationhere varied from complete neurological normalityto extensive neurological deficit.We shall now consider the various subgroups of

the two main groups in the following order:IA. Simple meningoceleIB. Meningocele with aberrant neural tissueIC. Meningocele with external fistulaID. Meningocele with haemangiomaIE. Meningocele with tethered rootsIF. Meningocele with tethered cordIIA. Meningocele with ectopic spinal cordIIB. Meningocele with ectopic spinal cord andtetheringIIC. Meningocele with total ectopia of spinal cord

SUBGROUP IA SIMPLE MENINGOCELES (Fig. I a) Thefour cases in this subgroup presented with a cysticswelling which was translucent, and which at operationwas found to have a narrow stalk emerging out of asingle spine. The defect in the spine was so narrowthat clinically it could not be palpated as a spina bifidaand, even after excising the mass and pushing in thestalk, it would not admit the tip of a finger. There wasno neurological deficit pre-operatively or post-operativelyin any of these. Histological examination carried outin three of these cases revealed the structure of a simplemeningocele, without any neural components. Theselesions varied in size and in site, being encountered indorsal, lumbar, or sacral spine. The amount of skincover also varied, being incomplete in two, but this hadno relationship to the histological features.

SUBGROUP IB MENINGOCELE WITH ABERRANT NEURALTISSUE (Fig. la) The four cases in this subgroupalso presented with a cystic swelling which was trans-lucent, and which at operation was found to have anarrow stalk emerging out of a spina bifida in a singlespine which was as narrow as in subgroup IA. Againthere was no neurological deficit either before or afterthe operation. This group also showed the variationin site and size of lesion and in skin cover, as in subgroupIA.The feature which distinguished this subgroup from

subgroup IA was the presence, on histopathologicalexamination, of aberrant nervous tissue, in one form oranother. In one instance there were ependymal canalsand large neurones (Fig. 2), suggesting the presence ofcord tissue. However, as there was no neurologicaldeficit before or after operation and as the cord wasnot even visualized at operation (in the D4 region),this was obviously aberrant central nervous tissue. Intwo other instances, besides abnormal neural or neuroglialtissue, derivatives of the mesodermal layer, such asabnormal smooth muscle masses or hamartomatousvessels (Figs. 3a, b) were observed. The fourth case witha fundal ulcer, showed, besides evidence of acute inflam-mation, one spinal ganglion with rootlets (Fig. 4).

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a SIMPLE MENINGOCELE: Subgroups IA,B

cover completeor incomplete

IN ONE SPINE

c MENINGOCELE WITH TETHERED ROOTS:Subgroup IE

u

° | Dural sac

LI] Line of e:

J% Roots in

t S Skin cover coor ic

() WIDE DEFECT IN ONEL

e ECTOPIC SPINAL CORD: Subgroup IIA

U

b MENINGOCELE WITH EXTERNAL FISTULAS:Subgroup IC

u

XC 0 | ~~NARR(

Li

d MENINGOCELE WITH

u

-Opening leaking CSF

-Skin cover completeor incomplete

IOW DEFECT IN ONE SPINE

TETHERED CORD:Subgroup IF

Kxcision

stalk

)mplete)mplete

E SPINE

FIG. 1. Main operative findings, in diagrammatic sagittalsections, in the various subgroups of meningoceles.U = upper end. L = lower end. The curved lines withinthe mass in (a) and (b) indicate the fibrous septa frequentlyfound.

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FIG. 2. (NP-D-830). Aberrant cord tissue and ependymalined canals in otherwise simple meningocele (H and E, x66).

SUBGROUP IC MENINGOCELE WITH EXTERNAL FISTULA(FIG. iB) Both the cases in this subgroup presentedwith a mass in the lumbar region, continually dischargingcerebrospinal fluid (CSF) through an opening on thesurface. Around the opening one case showed a rawirregular surface and the other had good skin cover. Atoperation the discharging fistula was seen to be the outerend of a track leading down to the neck of the lesionin the dural canal. There was no neurological deficiteither before or after operation, although the one specimenwhich was examined histopathologically revealed someabnormal degenerating root tissue. Both these childrendied of infection.

SUBGROUP ID MENINGOCELE WITH HAEMANGIOMA Thesingle case in this group presented with a cylindricalswelling sticking out like an umbilical cord above theskin surface, through a single (LA) spina bifida.The swell-ing consisted of a bluish vascular mass covered by athin membrane. At operation, the mass was foundattached to the dura by a firm stalk which filled the

FIG. 4. (NP-E-415). Part of an incipient spinal ganglionand some root tissue in a cystic space in the deep subcutisofa meningocele (Hand E, x 65).

defect in the spine. Histologically, it was a cavernoushaemangioma.

SUBGROUP IE MENINGOCELE WITH TETHERED ROOTS(Fig. Ic) Of the five cases in this subgroup informationof the anomaly at the first operation is available onlyin three cases, the other two being included on thebasis of a retrospective analysis. In the former threecases, the swelling was partly cystic, with a centralfirm tender mass, and it was only partially translucent.While clinically the spina bifida did not appear to belarge, at operation the defect was clearly wider than inthe preceding subgroups of cases, though confined toone spine. The defect was wide enough to admit athumb. The characteristic feature on opening thedura was the presence of recognizable nerve rootsclosely adherent to and forming a part of the deeperportion of the stalk. These roots formed a part of thefibrovascular matrix of the stalk. Histopathologicalexamination of the carefully dissected supra-radicularportion of the stalk and of the meningocele revealed

"O4-~~~~~

FIG. 3. (NP-D-973). (a) Nests of smooth muscle fibres and (b) ham2rtomatous vessels in fibrous matrix in the deepsubcutaneous part of meningocele (H and E, x 66).

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'Meningoceles' and 'meningomyeloceles' (ectopic spinal cord)

only fibrous tissue. Specimens from two other casesshowed in one instance an epidermoid cyst which hadformed by a process of invagination (Fig. 5) and inthe other some abnormal collections of striated andsmooth muscle fibres.

FIo. 5. (NP-E-760). Branching epidermoid cyst enteringsubcutaneous tissue ofmeningocele (Hand E, x 66).

The meningocele in two of the cases had completeskin cover, in one there was a small raw area with sur-rounding thin membrane, another had a large areacovered by thin dry membrane and in the fifth no in-formation was available. When the membrane waspresent, it was encircled by a thick ridge of subcutan-eous tissue, much like the ridge seen in ectopic spinal cord(see later).

The two cases which have been included on retro-spective analysis had neurological deficit which wasbelieved to have resulted from the first operation. Thedeficit was in the form of sphincter disturbance andperianal anaesthesia only, suggesting the involvementof a few sacral roots. In one of these cases the spinabifida was noted at the second operation to be wide, butrestricted to one spine.

SUBGROUIP IF MENINGOCELE WITH TETHERED CORD(Fig. ld) The meningocele in all five cases presentedas a large tender swelling in the lumbar or lumbosacralspine. All had a wide spina bifida, clearly palpable as adefect of at least three spines. Four of the five patientswho were between the ages of 1j years and 9 years atthe time of examination manifested neurological signsin the form of paraparesis, wasting, sphincter disturbance,and anaesthesia. Maximal wasting with contracturesand trophic ulceration were seen in the oldest child.By contrast, the fifth case examined at the age of 13 daysshowed no neurological signs.At operation in all the five cases the mass was found

adherent to the dural sac and through it to the spinalcord. This meant that the spinal cord was down at thelevel of the bony defect which was in the lower lumbaror sacral spines. This constituted a form of tetheringdown of the spinal cord. While in four of the cases itwas the lower end of the cord which was seen to expandout to form the deeper part of the stalk of the mass, inone instance the base of the mass was adherent to aslightly higher level of the cord which had been pulledout into the mass (Fig. 6).

HIG. 6. View at operation of the meningocele (L4 to SI) as seen from the right side of the patient.The tethered spinal cord has humped out of the spinal canal and is adherent to the under surface of themass (which is gently hooked to the left); the roots are also stretched and tethered. The cord assumesan inverted 'U' shape as it extends caudally (towards the right) beyond the tether.

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(a) (b)FIG. 7. (a) Anteroposterior and (b) lateral views of myelogram, showing the wide dural sac. (b) shows the spinal rootscoursing horizontally from the spinal cord, which was found adherent to the posterior wall of the dural sac. (a) showsthe lower end of the cord as a filling defect on one side of the midline.

Clinically, two cases showed peripheral cystic compon-ents to the swellings which at operation were confirmedto be meningeal sacs filled with CSF. The central firmand tender part of the swelling was directly adherentto the dural sac underneath and was capped by a lipo-matous mass. In two other cases the swelling was softand non-cystic throughout. At operation, this swellingconsisted mainly of a lipomatous mass with a centralstalk. The fifth case, who had an earlier operation else-where for excision of a 'lipoma', probably belonged tothe second category. The latter thiee cases had a bulkydural sac, although it was accommodated in the widenedspinal canal. This feature was obvious on the plainradiographs of the spine, in the form of widened pedicles.

Myelography done in one of tie cases demonstratedthe enlarged dural sac (Fig. 7a, b).

In two of the three cases where an operated specimenwas available for histological examination, small ir-regular islands of aberrant neurological tissue wereencountered amidst the fibrous tissue of the stalk andof the deeper part of the fatty cap respectively (Fig. 8).In the third case, clear teratomatous tissues were detectedwith abnormal entodermal (intestine-like), mesodermal(cartilaginous), and ectodermal (abnormal CNS tissue)elements (Fig. 9a, b, c). In none of the cases was therea true lipoma. As four of the five cases showed a clearimprovement in the neurological status post-operatively,and the child without any pre-operative deficit showed

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-io. 9b)

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FIG. 9. (NP-E-573). (a) Mucin-laden cells of abnormalepithelium; (b) irregular masses of cartilage; and (c)nervous tissue with attempted lamination of some of thecells: in meningocele with tethered cord. ((a) Krajian'smuci-carmine stain, x 105; (b) same stain, x 40; (c)H and E, x 66).

FIG. 8. (NP-D-860). Irregular islands of neuroglialtissue amid masses of collagen in the deeper part of thefatty cap of the meningocele with tethered cord (Kluver-Barrera, x 66).

1t,.9.i

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no worsening, it became obvious that the neural tissueremoved was aberrant.

SUBGROUP IA MENINGOCELE WITH ECTOPIC SPINALCoRD (MENINGOMYELOCELE) (Fig. le) As expected, thisformed the largest subgroup and consisted of 22cases. As stated at the outset, the essential morbidanatomical feature of these cases was an exposure orectopia of spinal cord of greater or lesser extent. Whenexamined soon after birth, the spinal cord was found tobe without any covering in the midline. A thin membraneextended from the border of the exposed cord to theskin edge. In several cases, the upper skin edge wasdirectly adherent to the underlying spinal cord. Whenexamined some time after birth, the thin membrane aswell as the spinal cord, were seen to be covered bygranulation tissue or even frank slough. The onlycase operated on at the age of 4 months showed an epi-thelialized membrane and spinal cord.The spinal cord generally ended at a level lower than

the usual, even though it was not tethered down by thefilum terminale. In one case the cord ended at thelevel of S4 vertebra-that is, below the level of thelower end of dural sac at S2, and it was adherent to theposterior surface of the bodies of S3 and S4 vertebrae.The margin of the lesion was well defined, being made upof a thickened ridge of subcutaneous tissue, whichappeared to be at the junction of the dura and thedeep fascia. The spina bifida, as assessed both clinicallyand at operation, was very wide in all the cases and ex-tended over more than three spines.As expected, all cases presented with severe neurological

deficit, generally paraplegia, sphincter disturbance, andanaesthesia. That this was noticeable even in childrenexamined six hours after birth pointed to the vulner-ability of the exposed cord.As the surgical procedure was entirely reconstructive,

no material was biopsied for pathological examination,except for a small bit of dura in one case.

SUBGROUP IHB MENINGOCELE WITH ECTOPIC SPINAL

CORD AND TETHERING There were seven cases in thissubgroup, one of which was available for dissectionafter death. They all presented with an exposed spinalcord in a manner identical with that described in theprevious subgroup. The interesting feature in all thesecases was the presence of a prominent filum terminaleof varying thickness. In the necropsied case it was asthick as the lower end of spinal cord (Fig. 10). At op-eration, the filum terminale was attached to the sacrumin a variety of ways. The exact nature of this attachmentwas not clear in two cases, as the lesion was higher upand there was no opportunity to examine the posteriorsurface of the sacrum. In three, the attachment wasthrough a thick fibrous band, while in the other twoit was through a hard nubbin filling the lower end ofthe gap in the bifid sacral spine (Fig. 11).

In four of the cases a biopsy specimen of the tetheringtissue was available for histological examination. Intwo of these specimens cord tissue could be recognized,one containing ependymal cell groups within possiblyill-formed homogeneous cord tissue (Fig. 12), and the

FIG. 10. (NP-E-338). Dissected post-mortem specimenof lumbosacral region of 7-day-old baby, showing thinatrophied spinal cord (in the middle of the upper edgeof the picture) tapering down to a thick filum terminale,which then ends in the oval fibrous mass attached to thesacrum. (On the right of this is another irregular elongatedwhite mass, which is the iliac bone and which separatesthe cauda equina region from the dissected right glutealregion.)

other including mature spinal cord with anterior horncells and both spinal roots (Fig. 13). The cord tissuein the former seemed aberrant both from its appearanceand from the observation that the child did not showobvious clinical worsening after operation. In the thirdcase, the cartilaginous nubbin removed at operationwas confirmed to be cellular cartilage. In the fourthcase, the nubbin was found to consist of posterior rootand ganglionic tissue embedded in dense fibrous matrix.

All the cases in this subgroup were examined andoperated on in the first three days of life. They presentedwith wasting of one or both legs and a talipes deformity.This was not noticed in the cases belonging to theprevious subgroup. As all these cases also showed thetethering of the cord, this was probably responsiblefor the wasting. Five of the seven cases showed a kyphosisof the vertebral column at the site of the lesion.

SUBGROUP IIC MENINGOCELE W" ITH TOTAL ECTOPIA OFSPINAL CORD The only case in this group was a stillbomfoetus, who presented with a frog-like face and a grosslyill-developed and exposed brain, looking like a combina-tion of iniencephaly and anencephaly.

DISCUSSION

As stated at the outset, this study was promptedby the lack of clarity on the true nature of so-called'meningoceles' and 'meningomyeloceles'. Wehave attempted to show how the term 'meningocele'can legitimately include several varieties of con-genital pathological lesions involving the spinalcord, roots, meninges, and vertebrae in dorsal,lumbar, and sacral regions. These lesions include

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Firm nubbin

Attached tosacral spine3 cases

Lipoma

Fibrousattachment tobifid sacralspine

Attached toskin

2 cases

Fusedposteriorspine of S2

Attached tosacral body

1 case

FIG. 1 1. The attachment offilum terminale in ectopic spinal cord with tethering.

FIG. 12. (NP-D-767). Ectopic spinal cord with tethering;biopsy specimen from S2-3 leveL. Core of ependymalcells in what look0like a widened central canal in a ring

of (?) ill-formed cord tissue; the cells in this could be

fibroblasts or altered astrocytes (Hand E, x 25).

all congenital swellings that present through

posterior spina bifida. Lesions that remain strictlywithin the spinal canal, such as diastematomyelia,

are not included here. Where the exposure of the

spinal cord was the main feature of the lesion,with only a thin leptomeningeal membrane covering

it, we have described the condition as a meningocelewith ectopic spinal cord (our group II) to replacethe older inadequate terms 'meningomyelocele'and 'myelocele'. For all practical purposes thisgroup may be referred to as ectopic spinal cord

(ESC) only. The rest of the cases, without the

exposed spinal cord, comprse our group I and this

may be referred to as meningocele.

The essential morphological features of thesubgroups of group I are summarized in the draw-ings (Fig. 1). As detailed earlier, the commonfeature of subgroups IA, IB, IC, and ID was anarrow defect in a single spine. The importantvariable features were the occasional inclusion ofaberrant CNS tissue within the mass and theextent of skin cover. When there was incompleteskin cover and some granulation covered the rawarea, the appearance simulated that of ectopicspinal cord. However, the correct diagnosis couldbe readily established by palpation of the size ofthe bony defect. One of the varieties of 'openspinal meningocele' described by Chapman (1967),is very similar to that described by us as meningocelewith external fistula (subgroup IC). He too hasemphasized the proneness to infection of thesecases.

Considering these four subgroups together,six out of 11 cases showed abnormal inclusionsof tissues of ectodermal, mesodermal, or entodermalorigin, five of these being clearly tissues pertainingto spinal cord or roots (subgroups IB and IC);the sixth was a haemangioma (subgroup ID). Suchan inclusion of neural tissue, though aberrant andproducing no clinical deficit on excision, wouldseem to be inconsistent with the hitherto accepteddefinition of a meningocele as simply 'a hernialprotrusion of the meninges' (Dorland, 1965).

Subgroups IE and IF had the common featureof a wider spina bifida (Fig. 14). It seems noteworthythat, at least in our experience. a wide defect in asingle spine (subgroup IE) has always been in thelower lumbar or sacral regions, with tethering of

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FIG. 13. (NP-E-366b). Ectopic spinal cord with tethering;biopsy specimen from S2 level. Mature cord tissue withcentral canal in the centre and groups of anterior horncells. The haemorrhagic areas are a result of the operativeprocedure ([Hand E, x 25).

roots only; while a still wider defect in severalspines (subgroup IF) was always associated with atethering of the cord itself. Another importantclinical feature was tenderness on palpation of themass, which could be elicited even in the new born,and which disappeared afteroperation. At operation,especially when the mass was tender or when thespinal defect was wide, the dural sac was openedand the stalk of the mass was carefully examinedfor the presence of adherent roots or cord.The tethering of the cord or roots to the under-

surface of the meningocele was probably responsiblefor the neurological deficit in the cases of subgroupsIE and IF. The two cases of subgroup IE, whereparents reported neurological deficit, had probablysuffered inadvertant damage to the roots during thefirst operation. In the subgroup IF, as the neuro-logical deficit was most pronounced in the oldestchild and was non-existent in the new born, itseems reasonable to presume that greater damageto the tethered cord resulted from the increase withgrowth in the length of the spinal column. Walker(1944) suggested the same mechanism for theprogressive neurological deficit in a 23 year oldpatient with intraspinal lipoma adherent to thelower end of cord and roots. Streeter (1919) showedthat when the embryo reaches 30 mm in length,there begins a disproportion in the rate of growthbetween the vertebral column and the spinal cord,the former elongating rapidly.

It is interesting to note that in two of the threecases of subgroups IE and in all three cases ofsubgroup IF, where biopsy specimen was availablefrom the first operation, some abnormal or hamar-tomatous component of one or more of the threegerminal layers was detected. All three cases of

subgroups IF showed aberrant neuroglial tissue,with, in one, evidence of teratomatous tissue aswell. Thus, in a general way, meningoceles ofsubgroups IE and IF compared with those ofsubgroups IA to ID in respect of their content ofaberrant tissues. These histopathological findingsindicate that the defect in development of the spinalneural tube which results in the formation of themeningoceles, arises early in foetal life.Our observations also provide evidence that the

fibro-fatty mass which forms the body of thesemeningoceles (two cases of subgroup IE and allfive of subgroup IF), is not a true 'lipoma'. Invirtue of its content of a variety of hamartomatoustissues, it is at best a hamartoma. This has also beensuggested by Bouton, Martin, and Rickham (1966).The term 'lipoma of cauda equina', as used amongothers by Dubowitz, Lorber, and Zachary (1965),is best dropped. They have reviewed the literaturewell and shown how a fibro-fatty mass adherentto the lower end of the cord has been known forover 100 years. Their cases, as also many of thosedescribed by James and Lassman (1960) under theterm 'spinal dysraphism', are very similar to thoseof our subgroup IF. They could be described betterunder the term 'meningocele with tethered cord',as we have used it. The entity 'meningocele withtethered roots' does not seem to have been describedbefore.A comparison of the drawings of the morpho-

logical defect in subgroup IF with that in subgroupIIA shows the extent of similarity between them.The common features are a wide defect in thespine extending over at least three vertebrae (Fig.14), the presence of the spinal cord in the lesioneven when that is in the lower lumbar or sacralregion, and a consequent horizontal disposition

Subgroups I ABC,D

000

000

IE

000

) (

00

IF IIA,B

00

J \

) (/'0

0 0 0Narrow defect Wide defect Wider defectin one spine in one spine in several spines

FIG. 14. Diagrammatic view as seen from behind atoperation (and also radiologically) of the range of defectsin posterior spines. The wide defect in subgroups IF, IIA,andIIB often extendedover more than three spines.

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of some of the roots of the cauda equina in a wideintraspinal meningeal sac (Fig. 1). The most signifi-cant feature differentiating group II from subgroupIF was the absence of the skin cover and the under-lying mass, with resultant ectopia of the spinal cord.As indicated in the introduction, the term 'meningo-myelocele' appears to us highly unsatisfactory.While Cameron (1956) in his careful study ofnecropsy specimens of the spine and the cord in'spina bifida cystica' demonstrated clearly thatthe basic lesion in all cases of so-called 'meningo-myelocele' was in fact an open 'myelocele',he unfortunately retained the former term in hisfinal classification. Most subsequent medical litera-ture on this subject has tended to perpetuate thisterminology. Gardner (1968) in a recent evaluation,rightly drops the term 'meningomyelocele' infavour of 'myelocele', which he prefers 'becauseneural tissue constitutes the primary componentof the sac, the meningeal portion being entirelysecondary'.The neurological deficit in cases of this subgroup

was noticeable even in infants examined six hoursafter birth. This points to the vulnerability of theexposed cord before birth, during labour, and afterbirth. Sharrard, Zachary, Lorber, and Bruce(1963) clearly demonstrated that children operatedon during the first two days of life showed muchless residual paralysis than those operated on atthe age of 6 months. Considerations of the anatomyof this group of ectopic spinal cord and the practicalimplications of it have been published elsewhere(Talwalker, 1967).The seven cases of subgroup IIB presented a

clinical picture similar to that in cases of sub-group IIA, with the notable exception of the presenceof wasting of the leg muscles and of a talipesdeformity. Many also showed kyphoscoliosis. Whilethe spinal lesion here was again similar to that insubgroup IIA, at operation some form of tetheringof the lower end of the spinal cord was witnessedin all except one. The tethering mechanisms, sum-marized in Fig. 11 were different from those en-countered in subgroup IF, in that the tetheringbands and nubbins were now found attached tothe posterior surface of the body of the sacrum.This was reminiscent of the attachment of thenormal filum terminale which, in fact, appearedto be thickened. Streeter (1919) has shown that the'filum terminale represents that portion of thespinal cord, caudal to the second coccygeal segment,which has undergone dedifferentiation and hasfinally become converted to a fibrous strand'. It isconceivable that there was an arrest or inhibitionof this dedifferentiation in the cases we are describ-ing here, with the result that the filum terminale did

not become completely thinned out and fibrosed,but retained some neural tissue. The latter wasevident in the histological examination of thetethering tissues, as described under 'Observations'.The relation between this anomaly and the wastingof leg muscles is not clear. The wasting may be dueto the tethering and consequent stretching effect onthe cord during intrauterine development. It mustbe pointed out that in one case of subgroup IIB,where tethering was not noticed, it might have beenmasked by granulation tissue or been actuallyabsent.As the number of cases on which our classification

is based is rather small, it is possible that there maybe a few other subgroups which we may not haveeither come across or recognized. To that extentour classification remains open to elaboration.

SUMMARY

A clinicopathological study is presented on 51 casesof various types of 'meningocele' and 'meningo-myelocele'. The 21 cases of 'meningocele' (group I)fell into the categories of (A) simple meningocele(four cases), (B) meningocele with aberrant neuraltissue (four cases), (C) meningocele with externalfistula (two cases), (D) meningocele with haeman-gioma (one case), (E) meningocele with tetheredroots (five cases), and (F) meningocele withtethered cord (five cases).The term ectopic spinal cord is suggested in

place of 'meningomyelocele' (group II), as theformer term describes the main feature of thelesion. Of the 30 cases of ectopic spinal cord, 22were of the usual variety (IIA), seven showed ectopicspinal cord with tethering (IIB), and one case hadtotal ectopia of the cord (IIC).The frequent involvement of spinal cord and root

tissue, often ofan aberrant or hamartomatous nature,in group I, besides their invariable involvementin group II, point to a similarity between the twogroups, which have therefore been included underthe common designation of meningoceles.

We are grateful to the several physicians and surgeonsand the various hospitals in Bombay who referred thesecases to us. Thanks are due to Mr. V. Talwadkar andMiss P. Gomes, of the Neuropathology Unit, for thehistological and secretarial assistance respectively.

REFERENCES

Bouton, J. M., Martin, C. H., and Rickham, P. P. (1966). Hamartomaand spina bifida. J. paed. Surg., 1, 559-565.

Cameron, A. H. (1956). The spinal cord lesion in spina bifida cystica.Lancet,2, 171-174.

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Chapman, D. S. (1967). Open spinal meningocele. J. paed. Surg.,2, 171-179.

Dorland's Medical Dictionary (1965). 24th Asian Edition. Pp. 897and 971. Saunders Igaku-Shoin Ltd: Tokyo.

Dubowitz, V., Lorber, J., and Zachary, R. B. (1965). Lipoma of thecauda equina. Arch. Dis. Childh., 40,207-213.

Gardner, W. J. (1968). Myelocele: rupture of the neural tube. Clin.Neurosurg., 15, 57-79.

Greenfield, J. G. (1963). Syringomyelia and syringobulbia, in Green-field's Neuropathology, pp. 330-335. Edited by W. Blackwood,W. H. McMenemy, A. Meyer, R. M. Norman and Dorothy S.Russell. Edward Arnold: London.

James, C. C. M., and Lassman, L. P. (1960). Spinal dysraphism. Anorthopaedic syndrome in children accompanying occultforms. Arch. Dis. Childh., 35,315-327.

McMenemey, W. H. (1966). Spina bifida. In Systemic Pathology,vol. 2, p. 1234. Edited by G. Payling Wright and W. St. C.Symmers. Longman Green: London.

Sharrard, W. J. W., Zachary, R. B., Lorber, J., and Bruce, A. M.(1963). A controlled trial of immediate and delayed closureofspina bifida cystica. Arch. Dis. Childh., 38, 18-22.

Streeter, G. L. (1919). Factors involved in the formation of thefilum terminale. Amer. J. Anat., 25, 1-12.

Talwalker, V. (1967). Anatomy of meningomyelocele. Pediat. Clin.India, 2,50-53.

Walker, A. E. (1944). Dilatation of the vertebral canal associatedwith congenital anomalies of the spinal cord. Amer. J. Roent-genol., 52,571-582.

Willis, R. A. (1962). The Borderland of Embryology and Pathology,2nd edition, p. 154. Butterworth: London.

The February 1970 IssueTHE FEBRUARY 1970 ISSUE CONTAINS THE FOLLOWING PAPERS

The cerebrospinal fluid homovanillic acid concentrationin patients with Parkinsonism treated with L-dopaG. CURZON, R. B. GODWIN-AUSTEN, E. B. TOMLINSON, andB. D. KANTAMANENI

Relief of intention tremor by thalamic surgery KHAIRYSAMRA, JOSEPH M. WALTZ, MANUEL RIKLAN, MAXIMKOSLOW, and IRVING S. COOPER

Simple and complex finger movement performance ofpatients with Parkinsonism before and after a unilateralstereotaxic thalamotomy E. PERRET, E. EGGENBERGER,and J. SIEGFRIED

Colour imperception in unilateral hemisphere-damagedpatients GIUSEPPE scoTn and HANS SPINNLER

The familial incidence of intracranial aneurysms VIJAYK. KAK, COLIN A. GLEADHILL, and IAN C. BAILEY

A study of a patient who had alexia without agraphiaW. J. K. CUMMING, L. J. HURWITZ, and N. T. PERL

Changes in motor innervation and cholinesterase locali-zation induced by botulinum toxin in skeletal muscleof the mouse: differences between fast and slow musclesL. W. DUCHEN

The incidence of abnormality in control human periph-eral nerves studied by single axon dissection N. ARNOLDand D. G. F. HARRIMAN

Remarkable recovery of a steroid-responsive recurrentpolyneuropathy DARRYL C. DEVIVO and W. KING ENGEL

Changes in the forearm associated with median nervecompression at the wrist in the guinea-pig MARGARETH. ANDERSON, PAMELA M. FULLERTON, R. W. GILLIATT,and J. E. C. HERN

The prediction of recurrence in meningiomas M. RUFUSCROMPTON and PETER C. GAuriER-SMITH

Uric acid and serum lipids in cerebrovascular diseasePart 2: Uric acid-plasma lipid correlations JOHN PEARCEand HASAN AZIZ

Lymphocyte transformation induced in vitro by PHAand PPD in multiple sclerosis W. CENDROWSKI

Subdural haematoma after the treatment of chronichydrocephalus by ventriculocaval shunts R. D. ILLING-WORTH

A comparison of methohexitone and thiopentone inelectrocorticography R. PAUL and RUTH HARRIS

Congenital spinal arachnoid cysts. Report of twocases and review of the literature IFrTKHAR A. RAJAand JOHN HANKINSON

Steroid myopathy complicating McArdle's diseaseF. L. MASTAGLIA, J. P. K. MCCOLLUM, P. F. LARSON, andP. HUDGSON

The role of skin areas adjacent to extensor musclesin motor neurone excitability: evidence bearing onthe physiology of Babinski's response M. MICHAELGASSEL

Book Reviews

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