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Turkish Neurosurgery 4: 159 - 163. 1993 Tekkok: OssiBed Posterior Longirudinal Ligement
ossification of The Posterior Longitudinal Ligament As A RareCause of Myelopathy Among Turks: Report of A Cas e
iSMAIL H. TEKKÖK, KEMAL BENLI
Department of Neurosurgery. Hacettepe University School of Mediane, Sihhiye. Ankara 06100. TürkiyeRunning Title: Ossified posterior longitudinalligament
Abstract : The ease of a 63-year-old man who presented withBrown-Sequard syndrome plus posterior column defiats due toextensive ossifieation of the posterior longitudinal ligament isreported. Diagnostie evaluation included magnetie resonance imaging in addition to eonventional teehniques. The patient wassurgieally treated by corpeetomy and fusion using an anterior approaeh and made a complete reeovery. The oecuerenee of ossified
INTRODUCTION
Compressian of the spinal cord by ossification ofthe posterior longitudinal ligament (OPLL) wasoriginaily described by Key as early as 1838 (9).AfterTsukimoto's report of an autopsy case in 1960 (19),it was recognized as a clinical entity and similar caseswere reported thereafter in Japan, at where n42 patients with OPLL were registered between 1960 and1977 (15). Accordingly, it was long regarded as adisease of the Orient, with a prevalence of 2%amongthe Japanese, almost 1% among Koreans and 0.83%among the Chinese (7.10).OPLL is a very rare can dition among Caucasians (2.3.4,5.11,12,22),only 29 caseshad been reported, when Hanna and Watt reviewed the literature in 1979 (4).However, with increased use of computed tomography (CT) and recentlyof magnetic resonance imaging (MR) in the evaluation of cervical myelopathy, this disorder has becomemore frequently recognizable. Starting with Firrozniaet al (3) reporting eleven white patients, series ofCaucasians although rather smail compared to thoseof the Japanese, started appearing in the literature
posterior longitudinalligament and the diagnostie features are briefIy reviewed. With more widespread awareness of this entity andmore frequent use of magnetie resonance imaging. we believe moreeases will be diagnosed.Key words: Magnetie resonanee imaging. Ossincation. PathologicaPosterior longitudinal ligament. Spina eord compression
(2,5,8.12) with the total number stiil not exceedingsixty by 1992. We have recently encountered a caseof extensive OPLL presenting with myelopathywhich is the first case in the 33-year history of ourinstitutian. The purpose of this paper is to presentthe clinical, radiological and surgical findings of thisrelatively uncommon disease.
CASE HISTORY
A 63-year-old man presented with a two-monthhistory of rightsided weakness and difficulty in walking. He reported that a urinary catheter had to be inserted a week prior to adrnission because of difficultyin emptying his bladder. There was no history oftrauma.
Neurological examination on admissian showeda poorly-nourished man who was unable to stand.Global power was 1-2/5 in the right arin and 2/5 inthe right leg. There was marked increase in tane ofthe right leg. The biceps, triceps and styloradialreflexes could not be eliuted on the right. Deep tendon reflexes in the legs were brisk throughout.
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Turkish Neurosurgery 4: 159 . 163. 1993
Plantar response was upgoing bilaterally. Sensationto pin-priek and light touch was diminished belowC5 on the left. Vibration sense was impaired in bothlower extremities. There was gross atrophy of the intrinsic muscles of the right hand. Anal tone and analreflex were diminished.
The clinical diagnosis was lower cervicalmyelopathy and radiculopathy. Plain x-rays of thespine show ed a thiek ossification behind thevertebral bodies extending between C4 and C7 aswell as some spondylotic changes of the vertebralbodies (Fig. 1).An emergency CT-myelography withiohexol demonstrated compression of the spinal cordover several segments. There was massive posteriordisplacement of the cord with an anterioposteriordimension of 3 mm at C4-5 level (Fig. 2). MR imaging was performed on a 0.5T superconductive unit(Gyroscan. Philips Medical Systems. Netherlands),which confirmed the findings deduced from the CTmyelogram. The OPLL appeared as a thiek hypointense band behind the vertebral bodies C4-C7(Fig.3).
Buckling of the yellow ligament at C3-4 and C4-5contributed to spinal cord compression. creating an"hour glass" appearance.
Preoperative evaluation reve ale d obstructivepulmonary disease so surgery had to be postponedfor a few days for bronchodilator therapy and che stphysiotherapy. Meanwhile dexamethasone 4mg qdwas started. A skeletal survey to evaluate possiblelocations of diffuse idiopathic skeletal hyperostosis(DISH) proved negative. The patient subsequentlyunderwent surgery. With a classical anterior approach the anterior surfaces of the vertebral bodiesC4-C7 were exposed. Medial portions of vertebralbodies C4.5.6 and the upper portion of C7 were drilled creating a longitudinal canali 5 mm wide and 55mm long. As the vertebrectomy proceeded posteriorly. using the operating microscope, the dura was initially exposed at the site of relatively less cordcompression. Le. C7. working upwards with angledmicrocurettes. The OPLL was like an ivory-hardosteoma, but could easily be dissected from the duraand was completely removed. There was no spreadof ossification into the intervertebral foramina. An
autogenous graft from the ribs was fitted and securedin the drilled canal. and a rigid cervical collar wasappIied before the patient recovered fromanaesthesia. The postoperative course was un event-
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Tekkok: Ossifjed Postenoi Longimdinal Ligement
ful. There was no morbidity assodated with thedonor site. At 6 months postoperatively the patientis fully continent and able to walk with a cane.
DISCUSSION
The aetiology of OPLL and the reason why thereis a high incidence amongst the Japanese is stillobscure. Degenerative disc disease (13.14), trauma(19). chronic fluorine poisoning (18) , infection (17) ,dietary factors and disturbance of the caldummetabolism (21)have all been proposed but none hasbeen established as the cause. Cases in assodation
with ankylosing spondylitis have also been reported(16).On the other hand, an assodation between DlSHpreviously known as Forestier's Disease and OPLLhas long been recognized (16)which may suggest ahereditary diathesis of spinat1igament ossification.
Whatever the cause, impairment of spinal corddrculation appears to be most important in thepathophysiology of OPLL. The histopathology of thespinal cord in OPLL patients has been reported bya few Japanese authors (13.19). Macroscopically thecord was found to be anteriorly concave and flattened in these autopsy studies. By light microscopysevere infarction of the grey matter. ascendingdemyelination in the posterior columns, descendingdemyelination in the lateral columns and proliferation of hyalinized sm all blood vessels were found(13). These changes are similar to those found withcervical spondylotic myelopathy suggesting that bothresult from ischaemia upon reduction of the bloodsupply in the distal branches of the anterior spinalartery (23).
OPLL occurs predominantly in males with a maleto female ratio ranging between 2:1 and 4:1(5,8.10.13.14.15). When OPLL encroaches upon thespinal canal it may cause myelopathy due to compression or ischaemia and/or radiculopathy due tostretching of the nerve roots. OPLL is more likely tocause myelopathy in a canal aIready compromisedby congenital stenosis, spondylosis or hypertrophyof the yellow ligament (5). Myelopathy occurred in35-57%of cases in various series (5.8.10.14.15)and corresponds to a more than 60% compromise of thespinal canal. The ligament and in some instances theattached dura becomes caldfied and ossmed by enchondral caldfication. Mean age at diagnosis was47-55 in various series (5.8.10,20). In 70-95% of thecases ossmcation occurred in the cervical spine (3,20).
Turkish Neurosurgery 4: 159 - 163. 1993
Fig. 1 : Lateral pIain x-ray oE the cervical spine. SpinaI canaI ismarkedIy narrowed between C4 and Cl.
Tekkok: Ossjfjed Posterior Longitudinal Ligement
Cervical OPLL can be divided to segmental and continuous types. With the continuous type. an averageof three vertebrallevels are involved while in the
segmental type OPLL. the ossification is interruptedat disc levels. Patients with segmental type OPLL aremost often asymptomatic. but recognition of any typeis cruciaL.because even with slight injury. the cordcan easily be damaged.
A high index of suspidon is the best aid in thediagnosis of OPLL. It should be considered particularly in male patients over 40 years of age presentingwith radiculo- and/or myelopathy. The diagnosticc1ue for OPLL lies in careful inspection of the lateralplain x-rays of the spine for a dense ossified stripalong the posterior margin of the vertebral bodies.however OPLL may not be seen readily on plain xrays in every patient. Myelography may demonstratecord compression but fails to differentiate OPLLfromdisc hemiation or spondylosis. CT-myelography withsmall interslice intervals is invaluable for diagnosisand operative planning (5). So far only three reportsdealing with the MR characteristics of OPLLhave appeared in the literature (11.20.22). Though MR is accepted to be poor in detecting bony pathologies.longitudinal extension of the ossification is betterdemonstrated on MR scans than on plain x- ray s orCT scans. espedally in the lower cervical and upperthoradc spine. On Tl-WL. ossification appears as a
Fig. 2 : AxiaI Ct image after intrathecal iohexoI injection. SpinaI cord is compressed and dispIacedby thiek ossjfjcation oE OPLL. SagittaI diameter oE the spinaI cord is 3 mm.
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Turkish Neurosurgery 4: 159 - 163, 1993
Fig. 3: Sagittal T2-weighted MR image of the cervica1 spinedemonstrates the marked compressian of the corvica1spinal cord between levels C4-C6. OssiBed ligamentappears hypointense.
law signal and it is hard to differentiate slight ossification from cerebrospinal fluid. whereas OPLL may berecognized as an impression on high signalcerebrospinal fluid flow on T2-weighted images(11,20,23). Differential diagnosis of law signal intensity on both Tl and T2-Wl include caldfied meningioma and arteriovenous malformation (AVM). Ameningioma hardIyever spans several segments,while spinal AVM's are usually posterior and rarelycause compressian. MR findings of segmental andcontinuous types of OPLLalsa differ. Continuous cervical OPLL is more easily recognized at MR imagingthan segmental cervical OPLL.An average 6mm thickarea of hypointensity is the finding assodated withthe continuous type (20).According to Yamashita etaL.a band of intermediate to high signal intensitywithin areas of ossuication considered to representbone marrow can be observed in half of the cases
with continuous OPLL (20). however we could not
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Tekkok: ossifjed Posterior Longitudinal Ligement
identify such an increased intensity in our patient.In patients with segmental type OPLL, MR shows athin area of hypointensity. therefore the differentialdiagnosis between cervical disc herniation. hypertrophy of the posterior longitudinalligament. spondylosis and segmental OPLL is stili difficult with theuse of MR imaging alone (20).
The choice of surgical procedure for this entity.including laminectomy. laminoplasty and anteriordecompression with fusian. stili remains controversial. For alina st two decades after Tsukimoto's
popularization of OPLL. the preferred treatment wasposterior decompression (14.15). With the standardposterior approach. the dura was not opened narwere the dentate ligaments cut; no attempt wasma de to remove the anterior ossified mass (14). Intime. there appeared various concerns about laminectomy because with posterior decompression the rootsleeves were often seen to be kinked posteriorly bythe ossification making it necessary to remove themedial portion of the facets. The risk of subsequentinstability. delayed neurological deterioration andpersistence of radiculopathy due to remaining stretchof the nerve roots were the main causes of this
dissatisfaction. Laminoplasty appeared as an alternative to overcome the complications arising withlaminectomy (6.10). but it too is an indirect operation aiming at enlarging the canal. Posterior decompressian remained popular until Abe et aL.advocatedthe anterior approach in 19S1 (1).Corpectomy. discectomy and microscopic removal of OPLL followed byinterbody fusian is the currently used and most directapproach to the problem (5.S). Somatosensory evoked potential studies are now the established methodnot only in intraoperative monitaring but alsa inassessing the clinical course foliowing treatment(8.23). In conclusian, in reporting a case of OPLLevaluated by MR and treated with the contemporarysurgical method. our goal was to attract the attentionof our colleagues to the disease which is known tobe rare among Caucasians. With more widespreadawareness of this entity and more frequent use ofthin section CT-myelography and magneticresonance imaging. we believe more cases will bediagnosed.
Correspondence: Dr. 1smail H. Tekkok.Hacettepe UniversitesiTip FakultesiBeyin ve Sinir CerrahisiAna Bilim Dali SihhiyeAnkara 06100 Türkiye
Turkish Neurosurgery 4: 159 - 163, 1993
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