1 79
CT Identification of
Postlaminectomy
Pseudomeningocele
J. George Teplick 1
Robert G . Peyster
Steven K . Teplick
Lawrence R. Goodman
Marvin E. Haskin
A postlaminectomy pseudomeningocele is a spherical , fluid-filled space with fibrous
capsule lying dorsal to the thecal canal in the laminectomy opening that occasionally
develops after surgery. Eight cases were found in 400 symptomatic postlaminectomy
patients undergoing computed tomographic examination. The contents are of cerebrospinal fluid density and mayor may not have demonstrable communication with the
subarachnoid space. Whether they are the cause of symptoms is conjectural; none of
these eight patients had surgical removal.
A postlaminectomy pse udomeningocele apparently results from an inadvertent
meningeal te ar [1] during spinal surgery. Although uncommon , it has numerous
names in the literature, inc luding extradural cyst , extrad ural pseudocyst, spurious
meningocele , pseudomeningocele, iatrogenic meningocele, arac hnoid c yst, and
postoperative diverticulum. Postlaminectom y pseudomeningocele is a distinct
entity and should be distinguished from posterior herni ation of the intact the cal
sac through a bilateral laminectomy defect, although the latter is also occasional ly
referred to as a postoperative pseudomeningocele. Eight cases discovered on
computed tomography (CT) in our series of 400 postlaminectomy patients are
presented and the literature reviewed. We were unable to find any description of
postl aminec tomy pseudomeningocele in the CT literatu re.
Materials and Methods
This article appears in the March / April 1983
issue of AJNR and in the June 1983 issue of
In the co urse of spinal CT stu d ies on about 400 s,!mp tomatic postoperativ e pati enl s,
eight cases of postlaminectomy pseudomeningocele were discovered. In seven patients,
bilateral laminectomi es had been performed , two in the cerv ica l spin e and fiv e in th e lower
lumbar spine. A unilateral lumbar lam inec tomy was done in th e eighth patient. Th e pati ent s
were 27-69 years old and there was no gender preponderance. Th e postoperative scans
we re obtained from 1 month to 5 years after lamin ectomy . None of th e patien ts had surgica l
co nfirmation of the lesion.
All CT studies were perform ed on a General El ec tri c CT I T 8800 using a 9.6 sec
scanning speed. In the lumbar area, six 5-mm-thick sec tion s were ob tained at 4 mm
intervals throug h each disk space leve l. In th e ce rvi ca l area, 1.5-mm-thick co ntiguou s
slices we re employed.
Postoperative myelography was perform ed in four of th e eight cases, one ce rvi cal and
three lumbar. Metrizam id e' (Amipaque, Winthrop Labs, New York, NY) was used in three
cases, Pantopaq ue in one.
AJR.
, All authors: Department of Diag nosti c Radiology, Hahnemann University School of Medicine,
230 N. Broad St., Philadelph ia, PA 19102. Address reprint requests to J. G. Teplick.
AJNR 4:179-182, March / April 1983
0 195 - 6108 / 83 / 0402-0179 $00.00
© American Roentgen Ray Society
Results
CT Characteris tics
On CT , the postlaminectomy pseudomeningocele wa s a round ed area of low
density immediately posterior to the th ecal sac at th e site of a previous laminec-
180
TEPLICK ET AL.
AJNR: 4 , Mar ./ Apr . 1983
Fig . 1.-Postlaminec to my pseud o meningocele 5 years aft er laminectomy.
Uniform low-de nsity rounded area ( arrows ) d irectl y behind laminecto my site
in seq uential slices from L4- L5 has thin wall of hig her density and almost
appears to connec t with d ural sac in C . Density of contents is similar to th at
of th eca l sac. Lesion was almost sph eri cal, measuring 4 x 4 '12 cm.
Fig . 2 .-Pseudomeningocele at C5 in 47-yea r-old patient who had bil ateral lam in ec tomies 3 years befo re for herni afed disk at C5 and now has
bilaleral leg sy mpto ms. Pse udomeningocele is c learl y demo nstrated on suc-
cessive scans of C4 as round ed lucenc y ( arrows ) directl y behind theca l sac.
It has dense wall and is spheri cal (about 2 x 2 cm); it did not fill during
myelography , and its presence was unsuspected.
tomy (figs . 1 and 2). In the lumbar region , the contents were
simil ar or slightly lower in density th an that of the thecal sac.
In th e cervi ca l area, th e contents appeared sign ifi cantly
lower in density th an th at of the thecal sac , probably because th e sac contains th e spinal cord at this level. The
lesions appeared to be partly or c ompl etely contained with in
a capsul e, whi c h was denser th an its contents and usually
dense r th an th e surro unding tissu e (figs . 1 and 2), which
often separated th e postl aminectomy pseudomen ingoce le
from th e th eca l sac. Th e ca psul e was better visualized when
it was surrounded by fat (fig . 3) . The postlaminectomy
pseudomeningoceles ranged in size from 1 .5 x 2 cm to 4.5
x 5 .5 c m.
was demonstrated by metrizamide myelography or by CT
after intrathecal metrizamide instillation (fig. 4) . In the second case (fig. 5), rapid communication was noted fluorosc opically , filling the pseudomeningocele with metrizamide.
Th e premyelogram scout films revealed residual Pan topaque g lobules , which moved dependently with gravity
within the pseudomeningocele . In the third case , the pseudomen in goce le filled slowly with metrizamide, which was
seen on ly on delayed films . In the fourth patient, the postoperative cervical Pantopaque myelogram obtained elsewhere failed to show commun ication .
Myelographic Fea tures
Of th e four cases in whi c h postoperative myelography
was performed , three were studied at our institution and
avail abl e for review . In one case, no commun ication betw ee n th e subarachnoid space and th e pseudom eningocele
Clinical Features
In our CT series, the incidence of postlaminectomy pseudomeningocele was eight (2 % ) of the 400 postoperative
patients. The earliest pseudomeningocele was noted 1
month postoperatively . The o ldest was discovered 5 years
after surgery .
All si x patients with a lumbar pseudomeningocele com-
POSTLAMINECTOMY PSEUDOMENINGOCELE
AJNR:4, Mar./ Apr. 1983
Fig. 3. -Cervical postlam inectomy pseud omeningocele. A neurofibrom a
was removed from C1-C2 months before. CT was performed because of
rec urrence of sy mptoms. A round, lOW-de nsity area ( arrow ) is iust beh ind
. bilate ral laminec tomy at C2. A droplet of Pantopaqu e from preoperati ve
myelog ram is w ith in lesion. Dist inct dense capsule is best seen where
surroun ded by fat. Lesion was sph erical, about 3.0 x 2.5 c m.
Fig. 4.-Noncommunicating pseudomeningocele 5 months after lam inectomy . Continued bac k discomfort after disk ectomy led to di scovery of bulg e
overlying lumbar spine. CT shows c harac teri stic low-den sity rounded co ll ection (larg e white arrow) behind laminectomy, extend ing to posterior sk in
bulge ( sma ll white arrow) . Metriz am id e instilled in dural sac (black arrow) did
not enter pse udo meningocele. Lesion was abo ut 3 cm in di ameter and about
4 cm long . Absence of dense wa ll may reflect recent o ri g in of lesion.
plained of low back pain . Three also had radiat ing pain to
one or both legs and one noted focal swelling in the back at
the site of the pseudomen ingoce le. The two patients with
cervical pseudomen ingoceles had radicular symptoms in
the arms (unilaterall y in one case and bil aterally in the
other) .
Discussion
A postlaminectomy pseudomeningoce le results from an
inadvertent surgical dural tear. Some authors [2-5] bel ieve
A
B
Fig. 5. - Comm unica ting lum bar postlaminec tomy pesudomening oce le.
Multiple previous operatio ns we re performed on lumbar spin e, in cluding
attempted repa ir of CSF leak from dural tea r 2 yea rs before these exa mination s. Th e pat ient had low bac k pain radi ating to the ri g ht leg and headaches
induced by bending o r straini ng, wh ich were rel ieved by rec umbency. A,
Lateral view fro m lumbar metri zam ide myelog ram. Large pseudomeningocele
is fill ed with metrizam ide and residu al Pantopaque. B , CT 4 days aiter
mye log raphy . No defini te separatio n of les ion from th eca l sac is delin eated.
Interval since myelog raphy accounts fo r lack of metrizamide in lesion. Lesion
was 4 '12 x 5'12 c m.
th at arachnoid herniates through the te ar and proliferates to
form an arachnoid-lined sac fill ed with ce reb rospi nal fluid
(CSF) . Others [6- 8 ] conjecture that CSF extravasates into
the posterior soft tissue s through a tear th at extend s through
the arachnoid and eventually develops a fibrou s capsu le.
Perh aps both typ es ex ist, depending on the length of the
initi al tear.
A distinction should be made between postl amin ectom y
pseudomeningocele and simpl e posterior bulging of th e
intact th ecal sac through a bilateral lamin ectomy defect.
Th e latt er has also been ca ll ed a postoperative pseudo men-
Fi g. 6. - Postl aminecto my posteri or
hern iatio n of theca l sac. A, M etrizamide
myelog ram, lateral view, shows posterior
ex tensi on of thecal sac at L5 level ( arrow). B , CT at same level shows bu lg ing
of dural sac th rough lam in ectomy defec t.
Note elli psoid sac o n lower ri ght section ,
point of maximal bulging, and absence
of capsu le se parating herni ated part
from rest of sac. C, Met rizamide CT at
L5 in anothe r pati ent shows sim ple bulging of sac through lam inecto my defect
(arrows).
A
18 1
B
c
1 82
TEPLICK ET AL.
. ingocele (fig. 6), an unfortunate source of confusion.
Before th e advent of CT , myelography was the only
method that could identify a pse udomeningocele and then
on ly if th e communication with the subarachnoid space
remained open to permit the myelographic media to enter .
In our four cases with myelography, no commu ni cation
ex isted in two . Kim et al. [6] identified nine pseudomeningoceles in 21 patients 1 month after cervical laminectomy
using air myelography. In th e three cases he reexamined by
the same tec hnique 3 months after surgery, the lesions were
no longer identified, either because of c losure of the communi ca ti on or due to d isappearance of the pseudomeningocele . Swanson and Fincher [9] found an incidence of
0.07 % in 1,700 lamin ectomie s.
Persistence of the co mmunication between the pseudomeningocele and the subarac hnoid space may depend on
th e nature of th e lesion. Pseudomeningoceles that are due
to arac hnoid herni ation might be more likely to maintain this
communication [4], whil e in those with fibrous capsules,
eventual sealing off of th e CSF leak seems more likely.
The c linical significance of postlaminectomy pseudo meningocele is unclear. Many investigators [2,4,7 , 8] consid er
it a symptomatic lesion causing recurrent back pain and
rad icul ar irritation. Others [6, 10] believe that pseudo meningoce le should be suspected if the surgeon is aware of any
injury to th e dura during th e operation in a patient who
develops low back pain with rad iation after initially successful surg ery . In our patients, low back pain and/or radicular
symptom s led to th eir CT studies. The rol e of pseudomeningocele in produc ing th ese symptoms, however, is questionabl e since similar symptoms were present in all of our
400 postoperativ e patients exam ined. Rinaldi and Hodges
[4] reported relief of symptoms in three patients after surgical removal of pseudomeningoceles. None of our patients
AJNR:4,
Mar. l Apr. 1983
have had exc ision of their pseudomeningocele .
Although uncommon, postlaminectomy pseudomeningocele occurs more frequently than was suggested by previous
studies based on postoperative Pantopaque myelography.
CT is certainly the ideal method for demonstrating these
lesions. CT is noninvasive and will demonstrate a pseudomeningocele regardless of an existing commu nication with
th e thecal sac.
REFERENCES
1. Shapiro R, Robinson F. The spine. In : Teplick JG, Haskin ME ,
eds . Surgical radiology. Phil adelphia: Saunders, 1981 : 2699 -
272 4
2. Hyndman OR , Gerber WF. Spinal extradural cysts; congenital
and acq uired. J Neurosurg 1946; 3 : 474-486
3. Rin aldi I, Peach WF. Post-operative lumbar meningocele. J
Neurosurg 1969;30 : 504-507
4 . Rin aldi I, Hodges TO . Iatrogenic lumbar meningocele; report
of three cases. J Neurol Neurosurg Psychiatry 1970;33: 484-
49 2
5. Winkl er H, Powers JA. Meningocele following hemilaminectomy. NC Med J 1950;11 : 292
6. Kim YW, Unger JD, Grinsell PF. Post-operative pseudo-diverticular (spurious meningoceles) of the cervical subarachnoid
space. Ac ta Radiol [Oiagn] (Stock h) 1974;15: 16-20
7. Miller PR , Elder W . Meningeal pseudocysts (m eningocele spuriou s) following laminectomy . J Bone Joint Surg [Am]
1968;50: 276-286
8. Pag ni CA , Cassinari V, Bernasconi V. Meningocele spurious
following hemilaminectomy in case of lumbar discal hernia. J
Neuros urg 1961 ;18 : 709-71 0
9. Swanson HS , Finch er EF. Extradural arachnoidal cyst of traumatic origin. J Neurosurg 1947;4 : 530-538
10. Quencer RM , Tanner M , Rothman L. Th e postoperative myelogram . Radiology 1977;123:667-678