J. Neurol. Neurosurg. Psychiat., 1968, 31, 106-109

Intramedullary cystic lesions of the conus medullarisSAMI I. NASSAR, JAMES W. CORRELL, AND

EDGAR M. HOUSEPIAN

From the Department of Neurosurgery, College ofPhysicians and Surgeons,Columbia University, and the Neurological Institute of theColumbia-Presbyterian Medical Center, New York, U.S.A.

Intramedullary cystic lesions of the conus medullarisare rare. Although an extensive literature describessyringomyelia as being a frequent basis for cysticcervico-thoracic lesions it is apparent that thisdoes not occur frequently in the lumbosacral region(Kirgis and Echols, 1949; Netsky, 1953; Rand andRand, 1960; Love and Olafson, 1966). Poser (1956),in a review of 234 cases of syringomyelia, foundthat the cavity extended into the lumbosacral regionin only 12-6% and in only five cases were thecavities restricted to the lumbosacral segments.Some authors (Thevenard, 1942; Andre, 1951)question the occurrence of syringomyelia in thelower spinal cord. Nevertheless a high incidenceof constitutional defects has been noted amongsyringomyelia patients and members of theirfamilies, the most frequent of which are spina bifidaocculta,pes cavus, syndactylism, andchest deformities(Henneberg and Koch, 1923; Chavany and Thiebaut,1933; Thevenard and Coste, 1935; Jackson, 1949).These defects have been found to occur at times withcystic cavitations of the lumbosacral region, lendingsupport to the developmental aetiology of at leastsome intramedullary cysts.

Localized cysts of the conus and epiconus havealso been reported in association with trauma,tumours, and vascular disease (Kirgis and Echols,1949; Netsky, 1953; Hughes, 1966). Haemorrhageinto the substance of the-cord has been describedas a cause of cavitary disease following severetrauma. Liquefaction of the haemorrhage resultsin the formation of a fluid-filled cavity that mayremain unchanged or slowly enlarge at the expenseoffunctioning neural elements. Sudden haemorrhage,of course, results in a rapid progression of neuro-logical symptoms and the syndrome of haemato-myelia.

Cavitations may also be produced by vascularimpairment to the cord structure from extraneuralinflammatory or compressive pathology. Anotherprocess of cyst formation may be ischaemic necrosisof the cord with resulting liquefaction. Irrespective

of the aetiology, these cysts may simulate the clinicalpicture of syringomyelia.The cases of cysts of the conus medullaris re-

ported here simulated the clinical picture ofsyringomyelia, tumour, or lumbar disc disease.The radiographic findings in each case were inter-preted as indicating the presence ofan intramedullarytumour. The correct diagnosis was made in eachcase only at operation.

CASE REPORTS

CASE 1 (F.T., NO. 179 16 92) A 22-year-old negro malewas admitted complaining of weakness and pain in thelegs for three years. The pain began in the right foot andprogressed in nine months to involve both lower limbs.There was an associated feeling of numbness of both feet.One year before admission he complained of persistent

low backache which radiated to the right thigh and calf.This was followed by difficulty in voiding. The patientalso observed a progressive bilateral deformity of thefeet (pes cavus). His past medical history contributednothing.

General physical examination was normal. On neuro-logical examination this asthenic young man was foundto have bilateral foot drop. There was diffuse weaknessof both lower extremities, most marked in the calfmuscles. There was wasting of the small muscles of bothfeet, more pronounced on the right. The Achilles reflexeswere absent. The appreciation of pain and light touchwas decreased up to the level of L3 bilaterally, but thethird to the fifth sacral dermatomes were spared. Labora-tory studies were normal. The cerebrospinal fluidcontained 17 mg protein 100/ml./cu.mm and 1 W.B.C.Pantopaque myelography showed evidence of an

intramedullary tumour of the conus (Fig. la). At laminec-tomy (Tl1-LI) a 2 x 2 cm intrinsic mass of the conus wasfound ending in the filum (Fig. lb). The nerve roots werestretched over the mass, which was cystic. A number 26needle was inserted into the mass and 4 ml. of colourlessfluid was aspirated. The mass collapsed and the nerveroots became relaxed. A 1 cm linear incision made in thedorsal midline of the conus allowed inspection of thecavity in which there was no gross evidence of tumour,

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Intramedullary cystic lesions of the conus medullaris

FIG. la. Case 1: myelographic demonstration of the FIG. lb. Casel:anintrinsiccysticmassoftheconuswithintramedullary mass defect at the level of T12-LL. the stretched nerve roots overlying it exposed at operation.

FIG. 2a. Case 2: myelographic demonstration of a FiG. 2b. Operative photograph showing a cyst of thefusiform intramedullary tumour at the level of T12-LJ conus which has been opened and its cavity exposed.with a complete block to the flow ofPantopaque above.

and cell block of the cyst fluid was negative for tumourcells. No biopsy of the cyst wall was done. The post-operative course was uneventful. A follow-up of sevenmonths showed an improvement in motor, sensory, andbladder function.

CASE 2 (C. D., NO. 174 92 23) A 51-year-old woman wasadmitted because of episodic low back pain with radiationto the right lower extremity for eight years. In December1963 the patient noted weakness in the right leg. In 1964a 'disc operation' carried out in another hospital was

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Sami l. Nassar, James W. Correll, and Edgar M. Housepian

followed by temporary alleviation of the low back painbut she continued to complain of weakness in the rightleg and began to have numbness of the right foot andtoes. Several months before this admission the patientalso complained of pain in the left leg. Her past medicalhistory contributed nothing.On physical examination there was flattening of the

lumbar lordosis with moderate paraspinous spasm andtendemess in the lumbar region. There was a right footdrop with wasting of the anterior and posterior tibialperonei and extensor hallucis longus muscles on theright. Hypaesthesia was noted in the L5 dermatome inthe right foot. The right Achilles tendon reflex wasabsent. The rest of the neurological examination wasnormal.

Laboratory data were normal. A radiograph of thespine showed slight narrowing of the lumbosacral inter-space. The cerebrospinal fluid protein level was 28 mg/100 ml. W.B.C. 1; R.B.C. O/cu.mm. A Pantopaquemyelogram revealved a large tumour of the conus withcomplete block at T12-L1 (Fig. 2a).At laminectomy (Ti1-LI) a large cyst of the conus

medullaris was found. The cyst was entered through athinned portion of the conus and 15 ml. of clear, colour-less watery fluid was drained. Careful inspection of thecavity failed to reveal evidence of tumour (Fig. 2b).Biopsy of the cyst wall was negative for tumour andshowed only fragments of white matter. In the post-operative period, numbness and pain gradually disap-peared. The strength of the right leg improved withphysiotherapy. The patient is doing well one year afteroperation.

CASE 3 (A. L., NO. 158 74 76) A 16-year-old boy wasnoted to have a mild thoraco-lumbar scoliosis at the ageof 3. He was well and engaged in various sport activitiesuntil he was 14 years old when the scoliosis progressedrapidly. In June of 1962 a spinal fusion from T6 to T11was done. On the second post-operative day the patientwas unable to move his lower limbs: there was diffuseweakness and spasticity of the muscles of the lowerextremities, most marked in the quadriceps, hamstringsand iliopsoas on the left and the plantar and dorsiflexormuscles of the left foot were profoundly weak. Therewere bilateral Babinski signs and unsustained ankleclonus on the right. Position and vibration sense wereasymmetrically reduced in the lower extremities. Thepatient required bladder drainage.The cerebrospinal fluid protein level was 51 rng/

100 ml., and 1 W.B.C. and 5 R.B.C./cu.mm. Radio-graphs of the vertebral column showed marked rightT11-12 scoliosis. A myelogram showed an expandedcervical-thoracic cord with an additional bulbous expan-sion localized at the conus medullaris. The findings wereinterpreted as either a diffuse syrinx or an ependymoma.A Ti1-12 laminectomy revealed a rounded, lobulated

cystic mass adherent to the inferior aspect of the conusmedullaris. It became attenuated inferiorly, beingattached to the filum terminale for a distance of 3-5 cm.The cyst had a thin, transparent wall and contained clearfluid (Fig. 3). Superiorly the cyst was continuous with a

FIG. 3. Case 3: operative exposure ofa rounded lobulatedcystic mass adherent to the inferior aspect of the conusmedullaris.

rounded opening, suggesting a greatly dilated centralcanal, in the conus medullaris. A subtotal excision of thecystic lesion was done and the conus medullaris andcauda equina were decompressed.

Microscopic examination of the cyst removed atoperation showed that the wall of the cyst was formed bya layer of ependymal cells situated along one surface ofnarrow bands of glial tissue and it was concluded,thatthis was a cystic congenital malformation of the filumterminale.The post-operative course was uneventful except for

a urinary tract infection. Post-operatively the boy wasable to walk unassisted for short distances. In Decemberof 1966 the patient was reported to be attending college.Although a leg brace was used he was able to carry outall desired activities.

DISCUSSION

These patients presented with interesting and similarfeatures. All three had lumbar pain and paresisof the lower extremity, thought to be related totumour, intervertebral disc disease, and syringo-myelia respectively. The myelographic findings inthese patients showed intramedullary lesions inter-preted as being consistent with conus ependymoma.The finding at operation of localized cysts of theconus medullaris filled with colourless, cystic fluidin the three cases was unexpected. The protein con-centration and cytological examination of thecystic fluid and biopsy of the cyst wall was notconsistent with tumour as an underlying cause.

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Intramedullary cystic lesions of the conus medullaris

In the first case, a cystic cavity was found entirelylimited to the conus medullaris. A biopsy of thecyst wall unfortunately was not obtained. A neo-plastic process seemed unlikely in view of a normalprotein determination and a negative cytologicalexamination of the cyst fluid. The findings in thesecond case suggested the presence of a syrinx inthe conus medullaris because of the clear fluidfilling the cyst and the biopsy of the cyst wall whichrevealed only fragments of white matter withoutan inner ependymal lining. There was no openingfrom the cavity to suggest continuity with the centralcanal. In the third case the cyst projected from thetip of the conus medullaris in between the roots ofthe cauda equina. The enlarged conus noted atoperation contained a greatly dilated central canalwhich opened inferiorly and its ependymal liningwas continuous with the lining of the wall of thecyst. The fact that diffuse widening of the upperspinal cord was seen by myelography suggests thatthe intramedullary cystic process extended superiorly,and it seems possible that the hydromyelic cavityextended the full length of the spinal cord. Thismight fit into Gardner's theory of a developmentalanomaly of the hind-brain and failure of the foramenof Magendi to open (Gardner, 1965).The relationship of intramedullary cysts to

neoplasms remains unclear. Necrosis within thecore of the tumour, circulatory insufficiency, andoedema of the adjacent cord structure may resultin intrinsic localized cavitation. The surgical andpathological findings in these three cases do notsupport these possibilities.The slow clinical deterioration indicates a pro-

gressive process. Enlargement of the cyst is thoughtto be the basis for the increasing neurologicaldeficits and indicates that the cystic fluid was underpressure causing compression of the roots of thecauda equina. Drainage by incision and permanentcommunication of the cyst cavity with the subarach-

noid space is the treatment of choice (Kirgis andEchols, 1949).

In all three cases post-operative follow-up ofseven months, 18 months, and five years respectivelyhas shown substantial improvement of motor andsphincteric function.

SUMMARY

Non-neoplastic cystic lesions of the conus medullarishave been shown to simulate tumour, syringomyelia,and lumbar disc disease. Although the pathologyhas been localized by myelography, the diagnosishas been made only at operation. Surgical explora-tion, drainage, and decompression has resulted inimprovement and is the recommended treatment.

REFERENCES

Andre, M. J. (1951). ttudessurla syringomy6li6. Acta neurol.Psychiat.Belg., 51, 665-696.

Chavany, J. A., and Thiebaut, F. (1933). Panaris analgesiques dupied droit par syringomyelie lombo-sacree unilaterale chez unenfant de 11 ans. Rev. Neurol., 1, 176-182.

Gardner, W. James (1965). Hydrodynamic mechanism of syringom-yelia its relationship to myelocele. J. Neurol. Neurosurg.Psychiat., 28, 247-259.

Henneberg, R., and Koch, M. (1923). Zur Pathogenese der Syringom-yelie und uber Hamatomyelie bei Syringomyelie. Mschr.Psychiat. Neurol., 54, 117-140.

Hughes, J. Trevor (1966). Pathology of the Spinal Cord, p. 32. Lloyd-Luke, London.

Jackson, M. (1949). Familial lumbo-sacral syringomyelia and thesignificance of developmental errors of the spinal cord andcolumn. Med. J. Aust., 1, 433-439.

Kirgis, H. D., and Echols, D. H. (1949). Syringo-encephalomyelia;discussion of related syndromes and pathologic processes, withreport of a case. J. Neurosurg., 6, 369-375.

Love, J. G., and Olafson, R. A. (1966). Syringomyelia: a look atsurgical therapy. J. Neurosurg., 24, 714-718.

Netsky, M. G. (1953). Syringomyelia: a clinicopathologic study.Arch. Neurol. Psychiat., (Chic.) 70, 741-777.

Poser, C. M., (1956). The Relationship between Syringomyeila andNeoplasm. Thomas, Springfield, Illinois.

Rand, R. W., and Rand, C. W. (1960). Intraspinal Tumnors of Child-hood. Thomas, Springfield, Illinois.

Thevenard, A. (1942). L'acropathie ulcero-mutilante familiale. Rev.neurol., 74, 193-212.and Coste, M. (1935). Syringomy6lie lombo-sacree familialeprobable et spina-bifida occulga sacre. Rev. Neurol., 63, 195-206.

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