Cervicomedullary decompression for foramen magnum stenosis in achondroplasia

J Neurosurg (3 Suppl Pediatrics) 104:166172, 2006
Cervicomedullary decompression for foramen magnum
stenosis in achondroplasia
CARLOS A. BAGLEY, M.D., JONATHAN A. PINDRIK, B.S., MARKUS J. BOOKLAND, B.S.,
JOAQUIN Q. CAMARA-QUINTANA, AND BENJAMIN S. CARSON, M.D.
Department of Pediatric Neurosurgery, The Johns Hopkins University, Baltimore, Maryland
Object. Achondroplasia is the most common hereditary form of dwarfism, and is characterized by short stature,
macrocephaly, and a myriad of skeletal abnormalities. In the pediatric population, stenosis and compression at the
level of the cervicomedullary junction commonly occurs. The goal in this study was to assess the outcomes in chil-
dren with achondroplasia who underwent cervicomedullary decompression.
Methods. Forty-three pediatric patients with heterozygous achondroplasia and foramen magnum stenosis under-
went 45 cervicomedullary decompressions at the authors’ institution over an 11-year period. After surgical decom-
pression, complete resolution or partial improvement in the preoperative symptoms was observed in all patients.
There were no deaths in the treated patients. The surgical morbidity rate was low and usually consisted of a cere-
brospinal fluid (CSF) leak in patients in whom the dura mater had been opened (either intentionally or accidental-
ly). This problem was successfully managed in all cases with local measures (wound oversewing) or CSF diversion.
Conclusions. In this review the authors demonstrate that decompression of the cervicomedullary junction in the
setting of achondroplasia may be accomplished safely with significant clinical benefit and minimal morbidity.
KEY WORDS • achondroplasia • cervicomedullary compression • foramen magnum •
decompression surgery • pediatric neurosurgery
CHONDROPLASIA is an autosomal-dominant, inherited
milestones at a slightly slower pace than do unaffected indi-
dwarfism syndrome characterized by short stature,
viduals.10 In addition, nonskeletal abnormalities may mask
Amacrocephaly, shortening of the extremities, and a or confound the clinical picture. For example, patients with
cluster of other skeletal abnormalities. This disorder is due
achondroplasia may often suffer from concurrent central
to a point mutation in the gene for the fibroblast growth fac-
and obstructive apnea attributable to neurological compres-
tor receptor on chromosome 4 and affects one in 26,000
sion (central apnea) and upper airway causes such as micro-
live births annually.3,8,19 Although the gene is inherited in an
gnathia and tonsillitis (obstructive apnea).
autosomal-dominant manner, approximately 75% of cases
In this paper we review our clinical experience with the
are due to a new, sporadic mutation.3 When sporadic muta-
surgical treatment of symptomatic cervicomedullary com-
tions occur, they are almost always associated with the pa-
pression over an 11-year period (1993–2003) in pediatric
ternal allele, which is consistent with the association of this
patients with achondroplasia. We identified 43 patients from
disorder with advanced paternal age.
our database who were treated during this period, and our
Patients with achondroplasia are susceptible to neurolog-
clinical experience with these individuals is presented here.
ical compression at a number of levels along the neuraxis.
In the pediatric population, one region commonly affected is
Clinical Material and Methods
the craniocervical junction. Neurological dysfunction may
result from compression on the brainstem or upper cervical
The records of all pediatric patients with heterozygous
spinal cord in this setting.
achondroplasia who underwent neurosurgical treatment at
The manifestations of neurological dysfunction in this
our institution between 1993 and 2003 were reviewed ret-
patient population may be subtle and difficult to detect clin-
rospectively. Forty-three patients who underwent cervico-
ically. Patients with achondroplasia are well known to be
medullary decompression during that 11-year period were
hypotonic during early infancy, and they achieve motor
identified. The charts of these patients were reviewed for
all demographic data and presenting symptoms.
Abbreviations used in this paper: CSF = cerebrospinal fluid;
EVD = extraventricular drain; ICP = intracranial pressure; MR =
Patient Population
magnetic resonance; SSEP = somatosensory evoked potential; VP =
ventriculoperitoneal.
Of the 43 patients identified from our database of children
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Cervicomedullary decompression for foramen magnum stenosis
with achondroplasia who underwent a cervicomedullary
the surgical procedure. The SSEP modality was used rou-
decompression, 16 were girls and 27 were boys. The mean
tinely throughout the positioning and the surgical proce-
age at the time of operation at our institution was 70 months
dure. A midline suboccipital incision and a subperiosteal
(range 2–199 months), and the mean duration of symptoms
dissection were made to expose the occiput and the arch of
was just longer than 7 months (range 1–12 months). One pa-
C-1. Care was exerted to avoid removing the muscle attach-
tient was clinically asymptomatic, yet had evidence of se-
ments to the C-2 spinous process whenever possible.
vere cervicomedullary compression on MR imaging.
The occiput and the midline posterior arch of C-1 were
removed using a high-speed drill and small curettes. The
Clinical Evaluation
bone removed was limited to approximately 3 cm in width
to avoid the complications of cerebellar sagging or cranio-
The clinical evaluation in all patients was performed by
cervical instability. Invariably the posterior rim of the fora-
a multidisciplinary team that included pediatric neurosur-
men magnum was thickened, and its orientation was more
geons, pediatric neurologists, neuroradiologists, pediatri-
horizontal than usual. Once the bone removal was com-
cians, and pulmonologists. All patients underwent a thorough
pleted, the thickened reactive fibrous tissue band was care-
neurological examination preoperatively, with particular at-
fully separated from the underlying dura mater. Care was
tention to signs and symptoms of brainstem or spinal cord
taken to avoid entering the dura at this stage of the opera-
compression. In addition, all patients underwent an MR im-
tion. Frequently, once this band was removed, the dura ma-
aging study of the craniocervical junction to assess the de-
ter was able to expand significantly from its previous posi-
gree of compression on the neural elements. Many of the
tion. Ultrasonography was then used to assess the adequacy
patients with suspected sleep apnea underwent overnight
of CSF pulsations around the brainstem.
polysomnography to help define central compared with
Adequate decompression was believed to have been ac-
obstructive origins.
complished when there was clear CSF space both ventral
and dorsal to the brainstem and upper cervical spinal cord as
Diagnostic Criteria
well as free pulsation of the neural structures. If compres-
The diagnosis of cervicomedullary compression was
sion remained at this stage of the operation, a duraplasty was
made based on neuroimaging criteria. The presence of this
performed by first making a midline incision in the dura
disorder on imaging studies may not necessarily imply clin-
mater. Copious venous bleeding was sometimes encoun-
ically relevant compression. Nonetheless, the clinical diag-
tered after incising the dura in this region because of the
nosis was made based on the combination of neuroimaging
well-developed circular sinus in young patients. This bleed-
findings and clinical symptoms. All patients included in this
ing was controlled using bipolar cautery or packing with a
review underwent MR imaging of the craniocervical junc-
hemostatic agent. Once adequate CSF pulsations were ob-
tion. The criteria used to make the diagnosis of cervicomed-
served, a paraspinous fascia graft was sewn in place. The
ullary compression included the following: 1) the presence
wound was then closed in multiple layers. Once awakened
of signs or symptoms of chronic brainstem compression
from general anesthesia and when movement in all four ex-
(such as apnea, lower cranial nerve dysfunction, swallow-
tremities was confirmed, the patient was taken to the inten-
ing difficulties, hyperreflexia or hypertonia, paresis, or clo-
sive care unit.
nus); and 2) neuroimaging evidence of foramen magnum
stenosis with or without neurological manifestations.
Postoperative Evaluation
Postoperatively, the patients were observed carefully for
Surgical Procedure
improvement or resolution of their preoperative neurologi-
All patients with a diagnosis of clinically significant cer-
cal symptoms. Serial neurological examinations were per-
vicomedullary compression underwent a foramen magnum
formed prior to discharge. Patients were discharged when
decompression and upper cervical laminectomy, with or
they were stable medically and when all wounds appeared
without a duraplasty. The surgical procedure has been de-
to be healing well. Periodic follow-up data were obtained
scribed previously by the senior author (B.S.C.).1 Because
for all patients, either by return clinic visits or communica-
of the high incidence of CSF leaks and hydrocephalus in
tion with the referring primary care physician. Resolution
this patient population, individuals with neuroimaging or
or persistence of presenting signs and symptoms was deter-
clinical evidence of hydrocephalus underwent placement of
mined, and the patient’s neurological status was assessed.
a shunt or EVD prior to or at the time of cervicomedullary
decompression. When an EVD was placed, it was opened
to drain immediately postoperatively, and the drainage pop-
Results
off pressure was gradually increased over a 2- to 3-day pe-
riod. The drain was removed in patients who remained clin-
Clinical Findings
ically asymptomatic and without evidence of a CSF leak,
The most common presenting symptom in our patient
whereas those in whom symptoms of intracranial hyperten-
population was respiratory difficulty. Twenty patients
sion or CSF leakage developed underwent placement of a
(46.5%) presented with respiratory symptoms in the form
permanent shunt.
of excessive snoring or apneic breathing spells. As a routine
During the cervicomedullary decompression, the patients
part of the multidisciplinary workup for these patients, a
were placed prone after the induction of general anesthesia.
sleep study is often performed. Information regarding pre-
The head was carefully supported in a slightly flexed posi-
operative sleep assessments was available for 23 of our 43
tion on a well-padded pediatric horseshoe. Care was taken
patients. Findings consistent with obstructive sleep apnea
to ensure that no pressure was present on the eyes during
(15 patients) were much more common than those of cen-
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C. A. Bagley, et al.
tral apnea (seven patients). Four of the seven patients with
patient recovered without incident and did not require re-
central sleep apnea had concurrent evidence of obstructive
placement of the shunt. In three other patients, clinically
apnea.
symptomatic hydrocephalus developed after decompres-
The next most common clinical findings were hyperre-
sion of the foramen magnum. One of these patients had pre-
flexia and clonus; these were present in 21 of 43 patients
viously passed a trial of EVD clamping. Nevertheless, this
preoperatively. Hypotonia was another common finding (12
patient continued to experience progressive ventricular en-
of 43 patients). Although hypotonia is a common finding in
largement, and a shunt was implanted without incident on
infants with achondroplasia, these 12 individuals were be-
postoperative Day 9. Another patient in whom the ventri-
lieved to have hypotonia that was not within the normal dis-
cles were enlarged preoperatively experienced a persistent
ease-specific range. Frank motor weakness was demonstrat-
CSF leak postoperatively that was refractory to local mea-
ed in 10 patients on their preoperative assessments.
sures (that is, wound oversewing and revision), and this pa-
Our patients’ parents often noted that these infants pre-
tient therefore underwent shunt implantation with complete
ferred to sleep with their heads extended (10 patients). Ad-
resolution of the leak.
ditionally, eight patients were noted preoperatively to have
The overall infection rate in our group of patients was 9%
delayed attainment of developmental milestones, as is com-
(four patients). In one of those in whom an infection devel-
mon for children with achondroplasia.
oped, a VP shunt was placed before the cervicomedullary
decompression. All patients who experienced this compli-
Surgical Results and Complications
cation had evidence of a CSF leak postoperatively. The pa-
tient who had previously undergone shunt placement expe-
No surgery-related death was noted among the patients in
rienced leakage from the suboccipital incision line. In one
this study. The mean length of stay postoperatively was ap-
other patient, leakage occurred from the suboccipital inci-
proximately 14 days (range 3–48 days). The most common
sion site, and in the other two there was a CSF leak from the
surgical complication encountered was a CSF leak; this oc-
exit site of the EVD that had been placed at the time of sur-
curred in seven patients. In three cases, the leak occurred
gery.
from the exit site after removal of the EVD. In the other
In one patient a pseudomeningocele developed in the
four patients who experienced this complication, the leak-
suboccipital region that required a repeated surgical explo-
age arose from the suboccipital incision. Two infections oc-
ration. The source of the CSF egress was located and sealed
curred in patients in whom a CSF leak from the EVD exit
using suture closure and fibrin glue. This patient had no
site had developed, and two occurred in those with leakage
further complications and was discharged with no other in-
from the suboccipital incisions. All infections responded to
cidents.
a culture-specific course of intravenous antibiotic drugs.
We encountered no clinical cases of postoperative cran-
No patient experienced a clinical deterioration immedi-
iovertebral instability among our group of patients. As a
ately after surgery, but symptoms returned in five after a
matter of course, we do not typically evaluate our patients
period of improvement. In these patients, repeated neuro-
for instability in the absence of symptoms after cervico-
imaging and surgical exploration demonstrated recurrent
medullary decompression.
stenosis of the foramen magnum. This residual compres-
sion was caused by both osseous and soft-tissue structures.
Clinical Follow-Up Duration
All five patients responded well to a repeated operation and
had complete resolution of their symptoms. One patient ex-
The mean duration of follow up was 62.5 months (range
perienced a transient seventh cranial nerve palsy and anoth-
1–123 months). Two patients were lost to clinical follow-
er had a transient fifth cranial nerve palsy of unclear origin.
up review after the initial postoperative visit and were
Both patients attained complete resolution of these cranial
therefore excluded from analysis. At the time of the last fol-
nerve deficits before discharge.
low-up evaluation, no patient had experienced a clinical re-
Twenty patients exhibited neuroimaging and/or clinical
turn of symptoms.
signs or symptoms of hydrocephalus. Nine of them exhibit-
ed clinical symptoms from hydrocephalus before cervico-
Discussion
medullary stenosis, and therefore had undergone VP shunt
placement prior to foramen magnum decompression. Eight
Patients with heterozygous achondroplasia have a high-
patients had neuroimaging evidence of hydrocephalus at the
er mortality rate for all age groups when compared with un-
time of foramen magnum decompression, and therefore an
affected individuals.10 In patients 4 years of age and young-
EVD was placed at surgery. After a period of ICP monitor-
er, there is a disproportionately high incidence of sudden
ing postoperatively, only two of these eight ultimately re-
infant death syndrome, which is believed to be caused at
quired placement of a VP shunt. In one of these two patients
least in part by neurological compression at the level of the
a shunt infection subsequently developed, which required
cervicomedullary junction.3,10,12 Furthermore, in the 5- to
removal of the device, placement of an EVD, and intraven-
24-year-old age group, central nervous system and respira-
ously administered antibiotic drugs. Surprisingly, this pa-
tory causes of death account for approximately one half of
tient tolerated prolonged periods of EVD clamping without
all cases.3,10
clinical deterioration or significant ICP spikes, thus result-
Determining which patients are most at risk for neuro-
ing in removal of the EVD and shunt independence.
logical problems is difficult in some cases. Some authors
An infection developed 2 weeks postoperatively in a pa-
have used the absolute dimensions of the foramen magnum
tient in whom a shunt had been implanted before decom-
as a guideline, whereas others have not found this to be
pression; this complication required readmission, intraven-
helpful in many cases.5,10 Only one of our patients had no
ous antibiotic medications, and removal of the shunt. The
clinically detectable signs, despite significant neural com-
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Cervicomedullary decompression for foramen magnum stenosis
pression seen on MR images obtained in this individual. We
radiographic evidence of significant neural compression.
believed that “prophylactic” surgery was warranted in this
Early detection and treatment of these patients may prevent
case, given the impressive imaging findings. This patient
unnecessary deaths or permanent neurological injury.2 As
experienced no adverse effects from the operation and was
with our group of patients, surgical decompression can of-
developing normally 18 months postsurgery. Other authors
ten completely alleviate many respiratory symptoms and
likewise believe that prophylactic surgery is warranted in
thus reduce the risk of sudden death.
cases of severe compression, given the high incidence of
sudden infant death in this patient population.6,18
Neurological Manifestations
Neurological manifestations are identified in as many as
Cervicomedullary Stenosis
50% of patients with achondroplasia.12 Symptoms may be
Stenosis at the level of the foramen magnum begins early
subtle and nonspecific even in the face of severe compres-
in infancy. Studies have demonstrated that the foramen
sion in some children. Infants may experience hypotonia,
magnum is comparatively small at birth in patients with
feeding problems, and poor head control. Because hypoto-
achondroplasia.4,16 Furthermore, severely impaired growth
nia and motor delay are characteristic, determining when
of the foramen magnum is seen in these patients during the
these signs may indicate cervicomedullary compression
1st year of life. This is due not only to the defect in endo-
may be difficult. Hyperreflexia and clonus, when present,
chondral bone formation that is pathognomonic of achon-
have been found to correlate directly with significant cervi-
droplasia, but also to the abnormal placement and prema-
comedullary stenosis and the need for decompression of the
ture fusion of the synchondroses.4,7,15 Displacement of the
foramen magnum.10 After thorough neurological examina-
two posterior synchondroses and their premature fusion is
tions we found evidence of hyperreflexia and/or clonus in
believed to account, at least in part, for the thickened poste-
21 (49%) of our patients. Relative hypotonia, when present,
rior rim of the foramen magnum that is so commonly found
has also been shown to correlate with the need for surgical
at the time of surgery.
decompression of the foramen magnum. This decreased
tone may be difficult to detect at times. Frank motor weak-
Respiratory Dysfunction
ness is a less frequent finding; it was seen in 10 of our 43
Respiratory complications are reported in 10 to 85% of
patients, but when present it may be a harbinger of perma-
individuals with achondroplasia.9,11 Manifestations include
nent neurological sequelae. This is often due to the older
apnea, tachypnea, excessive snoring, cor pulmonale, recur-
age of patients with this finding and the more protracted
rent pneumonia, and sudden infant death syndrome.2 These
clinical course.
symptoms may result from primary pulmonary problems
Determining, based on neuroimaging criteria, which pa-
such as a small thoracic cage or airway obstruction, neuro-
tients are most at risk for symptomatic foramen magnum
logical compression, or a combination of factors. Compres-
stenosis remains difficult at best. Although the growth rate
sion of the brainstem’s respiratory centers may interfere
of the foramen magnum in patients with achondroplasia has
with central respiratory drive and cause central sleep apnea.
been shown to be different in symptomatic and asympto-
Additionally, compression of the lower motor neurons in-
matic individuals, this difference did not reach statistical
nervating the diaphragm and other respiratory muscles may
significance.4 In a prospective study of a cohort of patients
cause weak and ineffective respiratory efforts.1,11
with achondroplasia, it was found that longitudinal and
Sleep apnea was the most common presenting symptom
transverse measurements of the foramen magnum that were
among this group of surgically treated patients (53%). Cen-
below the diagnosis-specific mean on computerized tom-
tral sleep apnea was demonstrated in seven (30%) of 23 cas-
ography scans were an independent risk factor for the ulti-
es, and obstructive apnea findings were present in 15 cases
mate need for a cervicomedullary decompression.10 In-
(65%) on overnight polysomnography. This discrepancy be-
trinsic medullary or cervical signal changes on T -weighted
2
tween the percentage of patients presenting with subjective
MR images is a sign of severe pathological conditions and
respiratory symptoms and objective findings is not uncom-
possible irreversible damage. Untreated, these cases of se-
mon, and does not correlate with the eventual resolution of
vere pathological conditions of the spine may result in irre-
these complaints after surgical decompression.9 This is a
versible changes in the spinal cord and lower medulla. Fur-
higher incidence than has been found in other studies and is
thermore, histological changes are observed that are similar
undoubtedly due to the fact that this group was composed
to those seen with traumatic central cord syndrome. These
purely of patients requiring surgery. As observed in our pa-
changes are believed to be a result of arterial insufficiency
tients, there is often dramatic improvement in respiratory
rather than direct impact.20
symptoms soon after the surgical decompression is com-
Surgical Decompression
pleted.17 Nonetheless, some respiratory symptoms may per-
sist after adequate surgical decompression. This undoubt-
Familiarity with the altered anatomy of the cervicomed-
edly happens because of the multifactorial nature of this
ullary region in this patient population is essential. As dis-
problem in patients with achondroplasia. Other possible
cussed earlier, the posterior rim of the foramen magnum
contributing factors must therefore be considered and ad-
often has a much more horizontal orientation than one is
dressed before surgical intervention when respiratory symp-
accustomed to find (Fig. 1). In addition, the posterior lip of
toms are the primary presenting complaint.
the foramen magnum is often quite thickened. The use of
As discussed earlier, respiratory failure in the pediatric
the high-speed drill to perform the suboccipital craniecto-
population is responsible for more than one half of all
my makes this portion of the procedure much safer. Fur-
deaths among patients with achondroplasia. Given this fact,
thermore, the bone decompression should extend bilateral-
we believe that prophylactic surgery is warranted if there is
ly to the medial aspects of the occipital condyles to ensure
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C. A. Bagley, et al.
an adequate bone decompression. The total width of the
pressions in a smaller group of patients. In this previous
bone decompression is typically less than 3 cm. In addition,
study, a CSF leak developed in four (27%) of 15 treated pa-
meticulous care must be taken to define the plane between
tients and required permanent CSF diversion with a VP
the bone of the occiput and the posterior rim of the first cer-
shunt. It is for these reasons that we have stopped routine-
vical vertebra, and the underlying fibrous band and dura
ly performing a duraplasty as part of the surgical decom-
mater. Accidental injury to the dura mater with the high-
pression. Given the altered CSF dynamics and the relative
speed drill may add significantly to the morbidity of the
morbidity associated with a CSF leak, we have found that
procedure by creating a postoperative CSF leak.
this step entails a high risk. In addition, we have found this
Care must also be taken to avoid passing any instrument
step to be unnecessary to decompress the suboccipital re-
beneath the intact bone in attempting to define the underly-
gion adequately. Furthermore, the use of intraoperative ul-
ing plane. The degree of compression present and the small
trasonography to assess for residual compression at the
amount of space available for the neural structures at this
time of surgery aids in the decision whether to open the du-
level make such a maneuver particularly dangerous (Fig.
ra mater. Visualization of adequate CSF spaces on axial and
2). Our preferred approach is to use the high-speed drill to
sagittal ultrasound images can eliminate the need to open
thin the bone as much as possible, and then use the small
the dura and perform a duraplasty. In this group of 43 pa-
curette to flick gently the remaining rim of bone away from
tients, a duraplasty was believed to be warranted in only
the dura mater and underlying tissues.
two. Both patients went on to experience CSF leaks that
The need to take down the thickened, fibrous band pre-
were manageable by local maneuvers (wound oversewing).
sent between the bone and the dura mater cannot be over-
emphasized. This layer often causes significant constriction
Causes of Hydrocephalus
of the cervicomedullary junction. In our experience, once
Macrocranium has long been associated with achondro-
this band is removed, the dura mater significantly expands
plasia. With the development of neuroimaging techniques
and becomes much more pulsatile. This step may help avert
such as computerized tomography and MR imaging, it has
the need to perform a duraplasty, which increases the risk
become apparent that this head enlargement is due at least
of a postoperative CSF leak.
in part to the ventriculomegaly that is commonly seen in pa-
tients with achondroplasia. The altered CSF dynamics in
Risks Related to Duraplasty
patients with achondroplasia is believed to be a result of
The most common complication related to the surgical
venous outflow obstruction at the cranial base.14 This theo-
procedure was a CSF leak. It has been well described that
ry has been supported by studies reporting angiographic
patients with achondroplasia often have altered CSF flow
evidence of venous outflow obstruction at the level of the
dynamics. This is believed to be due, at least in part, to ob-
skull base. Additionally, obstructions at the levels of the for-
struction of venous outflow secondary to foraminal nar-
amen magnum and the fourth ventricular outlets have also
rowing at the skull base. The senior author has previously
been postulated to play a role.14,17
published his experience with cervicomedullary decom-
In our study we found radiographic evidence of ventric-
FIG. 1. Artist’s illustrations showing normal findings (left) compared with the findings in the cervicomedullary junc-
tion in patients with achondroplasia (right). Note the horizontal orientation of the posterior rim of the foramen magnum
in achondroplasia, causing kinking of the cervicomedullary junction. Also note the obstruction of the CSF space at the
level of the foramen magnum, which causes obstructive hydrocephalus. The area of bone removed during the cervico-
medullary decompression is depicted in green in the illustration of achondroplasia.
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Cervicomedullary decompression for foramen magnum stenosis
FIG. 2. Preoperative T -weighted (left) and T -weighted (right) MR images demonstrating the typical findings in the
1
2
craniocervical junction in patients with achondroplasia. Note the horizontal orientation of the posterior rim of the fora-
men magnum, causing kinking of the cervicomedullary junction. Also note the lack of CSF space at the level of the fora-
men magnum caused by the bone compression.
ulomegaly in 20 patients. Nine had undergone placement of
leakage was 15.5% in this group of patients (seven of 45
VP shunts before surgery for symptomatic hydrocephalus,
procedures). Two of the patients in whom duraplasties were
and one of these nine remained clinically asymptomatic
performed experienced leakage from the suboccipital wound.
after the shunt became infected and was removed. In eight
Additionally, the other patients in whom a leak developed
patients an EVD was placed at the time of surgery; howev-
had a dural fenestration at the time of surgery (two patients),
er, only two were found to have significantly elevated ICP
and in three there was leakage from the exit site where the
that would warrant CSF shunting. One of these two patients
EVD had been removed. This underscores the high leak po-
was subsequently able to have his shunt removed without
tential and the need to achieve watertight dural and wound
clinical symptoms after it became infected, leaving only
closures.
nine (21%) of the 43 patients shunt dependent at last fol-
low-up review. These findings are consistent with other au-
Intraoperative Ultrasonography
thors’ reports of a higher incidence of radiographically con-
We believe that the use of intraoperative ultrasonography
firmed ventriculomegaly than clinical hydrocephalus.12,14
is of tremendous benefit for surgical decompression in the
Many patients with achondroplasia will experience arrest-
setting of achondroplasia. Other authors have also report-
ed hydrocephalus and will remain asymptomatic clinically.
ed on the benefits of this intraoperative technique.13 After
Therefore, careful screening for signs and symptoms attrib-
completion of the bone and fibrous tissue decompressions,
utable to hydrocephalus should be performed before com-
ultrasonography allows real-time assessment of CSF spaces
mitting the patient to shunt implantation. Also, placement
around the brainstem and upper cervical spinal cord. Pul-
of an EVD at the time of surgery can allow direct ICP mon-
satility of the upper cervical spine and brainstem generally
itoring to determine which patients are likely to benefit
suggests a satisfactory decompression. If any indication of
from CSF shunting.
continued compression remains, the dura mater may be
The alteration in CSF flow dynamics increases the risk of
opened and a duraplasty performed to provide adequate
a CSF leak developing postoperatively. Our rate of CSF
space.
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C. A. Bagley, et al.
Intraoperative SSEPs
6. Keiper GL Jr, Koch B, Crone KR: Achondroplasia and cervi-
comedullary compression: prospective evaluation and surgical
In cases of severe compression of the cervicomedullary
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junction, SSEPs may increase the safety of this procedure.
7. Morgan DF, Young RF: Spinal neurological complications of
Intraoperative SSEPs were used in 29 of our 45 cases; in all
achondroplasia. Results of surgical treatment. J Neurosurg 52:
but two of these, the authors believed that the use of SSEPs
463–472, 1980
provided critical feedback throughout the positioning and
8. Moskowitz N, Carson B, Kopits S, Levitt R, Hart G: Foramen
surgical procedure. In two cases, however, the signals were
magnum decompression in an infant with homozygous achon-
difficult to establish and SSEP testing was therefore aban-
droplasia. Case report. J Neurosurg 70:126–128, 1989
doned. Both of these patients were profoundly myelopath-
9. Nelson FW, Hecht JT, Horton WA, Butler IJ, Goldie WD,
ic at the time of surgery, and one had tremendous intrinsic
Miner M: Neurological basis of respiratory complications in
achondroplasia. Ann Neurol 24:89–93, 1988
spinal cord changes at the cervicomedullary junction on T -
2
10. Pauli RM, Horton VK, Glinski LP, Reiser CA: Prospective
weighted MR images. There were no cases in which intra-
assessment of risks for cervicomedullary-junction compression
operative SSEPs were lost during the surgical procedure.
in infants with achondroplasia. Am J Hum Genet 56:732–744,
Based on our experience with other spinal procedures,
1995
however, this real-time feedback allows earlier intervention
11. Reid CS, Pyeritz RE, Kopits SE, Maria BL, Wang H, McPher-
(that is, blood pressure elevation or administration of ster-
son RW, et al: Cervicomedullary compression in young pa-
oid drugs) in the event of a problem.
tients with achondroplasia: value of comprehensive neurologic
and respiratory evaluation. J Pediatr 110:522–530, 1987
12. Ruiz-Garcia M, Tovar-Baudin A, Del Castillo-Ruiz V, Rodri-
Conclusions
guez HP, Collado MA, Mora TM, et al: Early detection of neu-
rological manifestations in achondroplasia. Childs Nerv Syst
Cervicomedullary compression is both a common and
13:208–213, 1997
potentially devastating occurrence in achondroplasia. In this
13. Ryken TC, Menezes AH: Cervicomedullary compression in
retrospective review we demonstrate that this complex
achondroplasia. J Neurosurg 81:43–48, 1994
problem can be treated safely, with minimal patient morbid-
14. Steinbok P, Hall J, Flodmark O: Hydrocephalus in achondro-
ity and tremendous clinical benefit. The need for a multidis-
plasia: the possible role of intracranial venous hypertension. J
ciplinary team approach involving pediatric neurosurgeons,
Neurosurg 71:42–48, 1989
pediatric neurologists, pediatricians, pulmonologists, gen-
15. Thomas IT, Frias JL, Williams JL, Friedman WA: Magnetic
eticists, and neuroradiologists cannot be overemphasized.
resonance imaging in the assessment of medullary compression
in achondroplasia. Am J Dis Child 142:989–992, 1988
Acknowledgment
16. Wang H, Rosenbaum AE, Reid CS, Zinreich SJ, Pyeritz RE:
Pediatric patients with achondroplasia: CT evaluation of the
We thank Ian Suk for his beautiful artwork in Fig. 1.
craniocervical junction. Radiology 164:515–519, 1987
17. Yamada H, Nakamura S, Tajima M, Kageyama N: Neurologi-
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