AJR 2002; 178:1281-1284
© American Roentgen Ray Society
MR Imaging of Popliteal Pterygium Syndrome in Pediatric Patients
Lane F. Donnelly1,
Kathleen H. Emery1 and
Twee T. Do2
1 Department of Radiology, Children's Hospital Medical Center, 3333 Burnet Ave.
Cincinnati, OH 45229-3039.
2 Division of Orthopedic Surgery, Children's Hospital Medical Center,
Cincinnati, OH 45229-3039.
Received August 8, 2001;
accepted after revision November 12, 2001.
Address correspondence to L. F. Donnelly.
Abstract
OBJECTIVE. Our purpose was to describe the use of MR imaging in the
evaluation of the positions of the popliteal artery and peroneal nerve in
children with popliteal pterygium syndrome for preoperative planning and to
describe the typical appearance of popliteal pterygium on MR imaging.
CONCLUSION. By depicting the popliteal artery and peroneal nerve
either in normal positions or abnormally located immediately adjacent to the
pterygium, MR imaging provides useful information for preoperative planning in
children with popliteal pterygium syndrome. The MR appearance of a popliteal
pterygium is that of a band of abnormal tissue extending from the ischium to
the os calcis that has signal characteristics of fibrous tissue often attached
to a belly of anomalous muscle.
Introduction
Popliteal pterygium syndrome is the association of genitourinary and
craniofacial anomalies with a webcausing connective tissue band extending from
the ischium to the os calcis
[1,2,3,4].
Surgical resection of the popliteal pterygium may be performed to relieve the
resulting flexion deformity of the lower extremity
[1,2,3,4].
With popliteal pterygium, the positions of the popliteal artery and peroneal
nerve are variable [1,
2]. The artery and nerve may be
in normal positions, remotely positioned in relationship to the pterygium, or
abnormally positioned posteriorly, in close proximity to the pterygium
[1]. Presurgical delineation of
these structures would be valuable in minimizing the chance that the artery
and nerve will be inadvertently transected during the procedure. We describe
two cases in which MR imaging (including MR arteriography) was used to
evaluate these anatomic variations.
Materials and Methods
The MR imaging studies from two children with popliteal pterygium syndrome
were reviewed before surgical resection of the popliteal pterygium and
correction of their flexion deformities. The first patient was a 1-month-old
male infant; the second was a 3-year-old girl. Both patients had complex
facial anomalies, genitourinary abnormalities, and popliteal pterygium. The
male infant had bilateral popliteal pterygia, which was worse on the left
side. The girl had a unilateral right popliteal pterygium and choanal
atresia.
MR imaging was performed with the patients sedated. The lower extremities
were placed in the head or torso phased array coil with the field of view
including pelvis to foot. Multiple sequences were obtained of the bilateral
lower extremities, including axial and sagittal T1-weighted images (TR/TE,
450/8; slice thickness, 3; gap, 1) and sagittal fast spin-echo inversion
recovery images (4,500/16; inversion time, 155 msec; slice thickness, 4; gap,
1). MR arteriography was performed using a two-dimensional time-of-flight
technique (46/6.1; flip angle, 60°) and was displayed as axial and
maximum-intensity-projection MR images.
The extent and signal characteristics of the pterygium were noted. MR
signal characteristics were compared with histologic examination of the
pathologic specimens after surgical excision.
The anatomic position of the popliteal artery, either normal or abnormal
posterior with proximity to the popliteal pterygium, was noted on both
T1-weighted and MR arteriographic images. The position of the peroneal nerve,
either normal or abnormal posterior with proximity to the popliteal pterygium,
was determined by following its course from its origin at the sciatic nerve on
the axial T1-weighted images. When it was normally positioned adjacent to the
pterygium, the anatomic relationship between either the popliteal artery or
the peroneal nerve and the pterygium was described.
At the request of one of the referring physicians, we obtained a
conventional arteriogram of the 1-month-old male infant to confirm the
vascular findings seen on the MR arteriogram. The findings on MR arteriography
and conventional arteriography were compared. In both patients, imaging and
surgical findings were correlated.
Results
In all three extremities with pterygia, popliteal pterygia were depicted on
MR imaging as abnormal posterior structures arising from the ischium,
traversing inferiorly in the posterior aspect of the popliteal fossa, and
terminating on the posterior aspect of the os calcis. Each of the three
pterygia was resected from the upper thigh to the lower calf to document the
anatomic distribution of the pterygia. In both patients, MR imaging revealed
that portions of the pterygium had parts that were narrow in diameter and low
in signal (Figs.
1A,1B,1C,1D,1E,1F
and
2A,2B,2C,2D,2E).
Pathology confirmed these portions to be fibrous tissue. In the boy with
bilateral involvement, the pterygia had a wider diameter in the mid
(superior-to-inferior) portion, whereas in the patient with unilateral
involvement, the opposite was true. In the girl, the mid portion was narrow
and low in signal, and the superior and inferior portions had wider bellies.
In these regions, the pterygia showed signal intensity on MR imaging that was
isointense to muscle on all pulse sequences, suggesting a muscular
"belly" (Fig.
1A,1B,1C,1D,1E,1F).
These parts of the pterygia were confirmed to be striated muscle on pathologic
examination, indicating that the pterygia are anomalous muscles with long
tendonlike connective tissues. Other musculature in the posterior thigh and
calf was normal both on MR imaging and at surgical exploration.
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Fig. 1A. —Bilateral popliteal pterygium (left side > right side) in
1-month-old male infant. Photograph of lower extremities shows left pterygium
as posterior web (arrows). Note deformed feet with syndactyly and
cleft scrotum with right hemiscrotum. Right pterygium is not well visualized
because of leg positioning. Right was much less severe than left
pterygium.
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Fig. 1B. —Bilateral popliteal pterygium (left side > right side) in
1-month-old male infant. Sagittal T1-weighted MR image of left leg shows
pterygium as structure (arrows) posterior to knee. Pterygium extends
from ischium to calcaneus. Pterygium is low-signal narrow cord at superior and
inferior portions and has wider belly of tissue in mid portion
(arrowheads) that is isointense to muscle in signal intensity.
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Fig. 1C. —Bilateral popliteal pterygium (left side > right side) in
1-month-old male infant. Sagittal T1-weighted MR image of right leg shows
pterygium as structure (arrows) posterior to knee. As on B,
pterygium contains cordlike low-attenuation areas as well as wider belly
(arrowheads) that is isointense to muscle in signal intensity.
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Fig. 1D. —Bilateral popliteal pterygium (left side > right side) in
1-month-old male infant. Axial T1-weighted MR image obtained at level of
distal femurs shows pterygium located posteriorly (white arrows).
Left pterygium is larger in diameter, with signal intensity that is isointense
to muscle. Right pterygium is small and low in signal intensity. Peroneal
nerves are seen as small low-signal structures (arrowheads)
immediately anterolateral to pterygium at 10-o'clock position on right and
2-o'clock position on left. Popliteal artery (black arrows) is
normally positioned, away from pterygium.
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Fig. 1E. —Bilateral popliteal pterygium (left side > right side) in
1-month-old male infant. Two-dimensional time-of-flight MR arteriogram
obtained in lateral projection with anterior on left and posterior on right
shows popliteal arteries to be normally positioned. Note that no arteries are
coursing in posterior aspect of leg.
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Fig. 1F. —Bilateral popliteal pterygium (left side > right side) in
1-month-old male infant. Conventional arteriogram of left lower extremity
reveals popliteal artery (arrowheads) to be normally positioned and
remotely located in relation to popliteal pterygium (arrows).
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Fig. 2B. —Right popliteal pterygium in 3-year-old girl. Sagittal
T1-weighted MR image of right leg shows pterygium as structure
(arrows) posterior to knee. Pterygium is low-signal narrow cord with
wider "belly" of tissue (arrowheads) at its superior
portion that is isointense to muscle in signal intensity. Similar belly of
tissue was seen inferiorly (not shown).
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Fig. 2C. —Right popliteal pterygium in 3-year-old girl. Axial
T1-weighted MR image obtained at level of distal femur shows posterior
position of pterygium (white arrow). Peroneal nerve is seen as small
low-signal structure (arrowhead) immediately anterolateral to
pterygium in 10-o'clock position. Popliteal artery (black arrow) is
normally positioned, adjacent to popliteal vein.
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Fig. 2D. —Right popliteal pterygium in 3-year-old girl. Two-dimensional
time-of-flight MR arteriograms obtained in oblique (D) and lateral
(E) projections show popliteal arteries to be normally positioned. Note
that no arteries are coursing in posterior aspect of legs.
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Fig. 2E. —Right popliteal pterygium in 3-year-old girl. Two-dimensional
time-of-flight MR arteriograms obtained in oblique (D) and lateral
(E) projections show popliteal arteries to be normally positioned. Note
that no arteries are coursing in posterior aspect of legs.
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In both patients (all three pterygia), the popliteal artery and posterior
tibial nerve were normally positioned (not adjacent to the pterygia) (Figs.
1A,1B,1C,1D,1E,1F
and
2A,2B,2C,2D,2E).
These findings were shown on both the axial T1-weighted images and MR
arteriograms. In the 1-month-old male infant, conventional arteriography (Fig.
1A,1B,1C,1D,1E,1F)
confirmed the normal position of the popliteal artery. In both patients, the
normal positions of the popliteal artery and posterior tibial nerve were
confirmed at surgery.
In both patients (all three pterygia), the peroneal nerve was shown to be
located in an abnormally posterior position, immediately adjacent to the
pterygium (Figs.
1A,1B,1C,1D,1E,1F
and
2A,2B,2C,2D,2E).
In all cases, the peroneal nerve was located anterolateral to the pterygium,
in the 10-o'clock position on the right and the 2-o'clock position on the
left. Location of the peroneal nerves was confirmed at surgery.
Discussion
The term "pterygium" is derived from the Greek word for wing,
pterygion, and refers to a winglike structure or abnormal triangular
fold of tissue. Pterygia can occur in various portions of the body including
the neck (webbed neck), eyelids, knee, elbow, and digits
[2]. Pterygia are associated
with a number of syndromes. Neck pterygia are associated with trisomy 21,
trisomy 13, and Turner's syndrome
[2]. Other syndromes
specifically associated with pterygia include popliteal pterygium syndrome and
Escobar syndrome (multiple pterygium syndrome)
[2]. Popliteal pterygium
syndrome is a rare, usually autosomal dominant disorder that represents the
association of a popliteal web with a combination of facial, genitourinary,
and skeletal abnormalities
[1,2,3,4].
Facial abnormalities include lower lip pits, cleft palate, micrognathia, and
choanal atresia. Genitourinary abnormalities include absent or cleft scrotum,
cryptorchidism, and ambiguous genitalia. Skeletal abnormalities include
syndactyly, other hand or feet deformities, scoliosis, and rib abnormalities
[2].
Popliteal pterygia are typically attached to the ischium and os calcis of
the foot [1]. Popliteal
pterygia may be incomplete in their superior-to-inferior extent. Pterygia may
be unilateral or bilateral and, when bilateral, may be asymmetric in their
anatomic extent, thickness, and tissue. Because pterygia result in an
activity-limiting flexion deformity of the knee, surgical resection of the
pterygium is often performed
[1]. The popliteal artery and
peroneal branch of the sciatic nerve are often abnormally positioned
immediately adjacent to or in the pterygium
[1,2,3,4].
It is helpful to know the exact position of these structures before attempting
surgical resection of the pterygium or correction of the contracture so that
these structures are not inadvertently transected during the surgery. Both
transection of the peroneal nerve and excessive stretching can cause
neurologic damage to the lower extremity
[1,
4].
MR imaging offers a means of screening the anatomic location of the
popliteal artery and peroneal nerves in patients with popliteal pterygium
syndrome who are being considered for surgery. MR arteriography is helpful in
depicting the relationship of the popliteal artery to the pterygium. To our
knowledge, this use of MR imaging has not been previously described. In all
three pterygia evaluated, MR imaging correctly showed the position of the
popliteal artery and peroneal nerve in relation to the pterygium. In addition,
the peroneal nerve typically lies in or at the posterior margin of the
pterygium [1,
4]. In all three pterygia in
our series, the peroneal nerve was located immediately adjacent and
anterolateral to the pterygium. With aids such as MR imaging, it may become
apparent that anterolateral is the more typical position of the peroneal nerve
in patients with pterygia.
In the literature, pterygia have been consistently described as being of a
fibrous-cord nature
[1,2,3,4].
On MR imaging, portions of each of the pterygia showed a low-signal cordlike
appearance, consistent with this description. In these parts of the pterygia,
fibrous tissue was confirmed histologically. However, in all three of our
pterygia, a belly of anomalous muscles was shown in portions of the pterygia
both on MR imaging and at histologic examination. The anomalous muscle may be
located at the mid portion of the limb or directly over the popliteal fossa.
This appearance should not be considered atypical.
In conclusion, MR imaging is most likely the imaging test of choice when
evaluating children who are being considered for surgical resection of a
popliteal pterygium or correction of contractures. The MR appearance of a
popliteal pterygium is that of a band of abnormal tissue extending from the
ischium to the os calcis that has signal characteristics of fibrous tissue
often attached to a belly of anomalous muscle along portions of the fibrous
bands. By depicting the popliteal artery and posterior tibial and peroneal
nerves either in the normal position or abnormally located immediately
adjacent to the pterygium, MR imaging provides useful information for
preoperative planning in children with popliteal pterygium syndrome.
References
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Oppenheim WL, Larson KR, McNabb MBB, Smith CF, Setoguchi Y.
Popliteal pterygium syndrome: an orthopaedic perspective. J Pediatr
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Taybi H, Lachman RS. Radiology of syndromes, metabolic
disorders, and skeletal dysplasias, 4th ed. St. Louis: Mosby,
1996; 411-413
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Froster-Iskenius UG. Popliteal pterygium syndrome. J Med
Genet 1990;27:320
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Maral T, Tuncali D, Ozgur F, Safak T, Gursu KG. A case of popliteal
pterygium treated along with nerve expansion. Plast Reconstr
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Abstract
Introduction
