AJR 2001; 177:1025-1029
© American Roentgen Ray Society
Congenital Pseudarthrosis of the Tibia in Pediatric Patients
MR Imaging
Andreas H. Mahnken1,
Gundula Staatz1,
Benita Hermanns2,
Rolf W. Gunther1 and
Michael Weber3
1
Department of Diagnostic Radiology, University Hospital, University of
Technology Aachen, Pauwelsstr. 30, 52074 Aachen, Germany.
2
Institute of Pathology, University Hospital, University of Technology Aachen,
52074 Aachen, Germany.
3
Department of Orthopedics, University Hospital, University of Technology
Aachen, 52074 Aachen, Germany.
Received March 29, 2001;
accepted after revision May 11, 2001.
Address correspondence to A. H. Mahnken.
Abstract
OBJECTIVE. The purpose of this study was to describe the
characteristics of congenital pseudarthrosis of the tibia on MR images of
infants and children and to assess the value of MR imaging in evaluating this
disease.
CONCLUSION. MR imaging of congenital pseudarthrosis allows
assessment of the type and extension of the disease. It is especially
recommended for the evaluation of periosteal and soft-tissue changes near the
pseudarthrosis.
Introduction
Congenital pseudarthrosis of the tibia is an uncommon entity with a
reported incidence of 1:140,000-1:250,000 neonates
[1]. Usually the disease
becomes evident within a child's first year of life but may be undetected up
to the age of 12 years [2].
Bilateral occurrence is rare
[3]; the fibula is affected in
one third of the patients [4].
Congenital tibial pseudarthrosis is characterized by segmental osseous
weakness, resulting in anterolateral angulation of the bone. The osseous
dysplasia leads to a tibial nonunion and, because of tibial bowing and reduced
growth in the distal tibial epiphysis, shortening of the limb occurs.
Treatment options depend on the type of the disease
[5] and include different
bone-grafting techniques, the Ilizarow method, electric stimulation, or
amputation. In our study, the MR imaging findings in pediatric patients with
untreated congenital pseudarthrosis of the tibia were assessed and correlated
to the type of the disease and the histopathologic findings after surgery.
Materials and Methods
From March 1999 to July 2000, five neonates and children (four boys and one
girl; age range, 1 month — 5 years) with previously untreated congenital
pseudarthrosis of the tibia underwent MR imaging in our hospital. The
diagnosis was established by clinical examination and conventional
radiography. According to the Crawford
[6] classification of
congenital tibial pseudarthrosis, type I, type II, and type III were seen in
one patient each, whereas two patients had pseudarthrosis type IV
(Fig 1). In three patients, the
fibula also was affected. Although Recklinghausen's disease was associated
with the pseudarthrosis in four of our patients, neurofibromas were not
evident at the site of pseudarthrosis.
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Fig. 1. —Drawings illustrate Crawford's
[6] classification of
congenital pseudarthrosis of tibia. Patients with all types present with
anterolateral bowing of tibia. In type I, the medullary canal is preserved.
Cortical thickening might be observed. Type II is defined by presence of
thinned medullary canal, cortical thickening, and tabulation defect. The
dominant finding in type III is a cystic lesion, which may be fractured. In
type IV, pseudarthrosis is present with tibial and possibly fibular
nonunion.
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All MR examinations were performed in a 0.5-T MR scanner (Gyroscan T5 NT;
Philips, Best, The Netherlands) with a surface coil. The examination protocol
included T1-weighted spin-echo sequences (TR/TE, 550/20), T2-weighted
spin-echo sequences (2300/90, in two patients), T2-weighted turbo spin-echo
sequences (3800/120, in three patients), and fat-suppressed MR sequences.
Fat-suppression imaging was performed in four patients with a short tau
inversion recovery (STIR) sequence (1400/30; inversion time, 110) and in one
patient with a T2-weighted selective presaturation inversion recovery (SPIR)
sequence (4100/20). A section thickness of 3 mm, a field of view of 200-250
mm, and a matrix of 192 x 256 were used. In four patients, gadolinium
(0.1 mmol/kg of body weight; Magnevist; Schering, Berlin, Germany) was
administered before a contrast-enhanced T1-weighted spin-echo sequence
(550/20) and an additional fat-suppressed T1-weighted spin-echo sequence
(800/20). The MR images were assessed retrospectively by two radiologists in
consensus. The MR appearance of the anatomy of the tibia and the adjacent soft
tissue as well as the signal-intensity characteristics of the pseudarthrosis
were evaluated. All patients underwent surgery, and the imaging findings were
correlated to the histopathologic findings of the pseudarthrosis specimen.
Results
On MR images, all patients showed an anterolateral bowing of the middle or
distal section of the tibia. The pseudarthrosis covered a length of 6-15 mm.
In two children with pseudarthrosis type I and II, respectively, the medullary
canal was preserved. Histologic specimens of the pseudarthrosis area showed a
thickening of the hypercellular and hypervascular periosteum in all
patients.
In the patient with pseudarthrosis type I, the diameter of the tibial bone
was only slightly reduced. The area of the pseudarthrosis appeared
hyperintense on fat-suppressed (Fig.
2A) and T2-weighted images and slightly hypointense on T1-weighted
images (Fig. 2B) with contrast
enhancement after administration of gadolinium. The soft tissue adjacent to
the pseudarthrosis showed a slightly increased signal intensity on
fat-suppressed and T2-weighted images and a reduced signal intensity on
T1-weighted images with contrast enhancement after administration of
gadolinium.
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Fig. 2A. —7-month-old boy with neurofibromatosis and congenital
pseudarthrosis of the tibia (Crawford
[6] type I). Short tau
inversion recovery image (TR/TE, 1400/30; inversion time, 110) shows
congenital pseudarthrosis of the tibia as hyperintense lesion
(arrowheads). Note diffuse edema (arrows) of soft tissue
ventral to the tibia.
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Fig. 2B. —7-month-old boy with neurofibromatosis and congenital
pseudarthrosis of the tibia (Crawford
[6] type I). T1-weighted
spin-echo MR image (550/20) depicts anterolateral bowing and circumscribed
cortical thickening of the tibia (arrows). Medullary canal is
preserved. Bone marrow in region of anterolateral bowing of tibia shows slight
hypointensity.
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In the patient with pseudarthrosis type II, the medullary canal was
narrowed by thickening of the cortical bone. The pseudarthrosis showed a
hypointense signal intensity on T1-weighted images. The pseudarthrosis area
was hyperintense on fat-suppressed and T2-weighted images, whereas the
surrounding soft tissue showed no pathologic changes on MR images.
In the patient with congenital pseudarthrosis of the tibia type III, the
pseudarthrosis was depicted as a hyperintense intraosseous lesion on
T1-weighted and T2-weighted images (Fig.
3A,3B,3C,3D).
Histologically, this lesion consisted of chondroid tissue with insufficient
ossification. The cortical bone was locally thinned but not disrupted.
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Fig. 3A. —1-month-old male neonate with congenital pseudarthrosis of
tibia (Crawford [6] type III)
without neurofibromatosis. Lateral radiograph of calf depicts characteristic
cystic lesion in distal part of tibia.
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Fig. 3B. —1-month-old male neonate with congenital pseudarthrosis of
tibia (Crawford [6] type III)
without neurofibromatosis. Lesion (arrows) appears isointense on
T1-weighted spin-echo MR image (TR/TE, 550/20).
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Fig. 3C. —1-month-old male neonate with congenital pseudarthrosis of
tibia (Crawford [6] type III)
without neurofibromatosis. On T2-weighted turbo spin-echo image (3800/120),
area of pseudarthrosis (arrow) appears hyperintense with thickened
hyperintense periosteum (arrowheads).
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Fig. 3D. —1-month-old male neonate with congenital pseudarthrosis of
tibia (Crawford [6] type III)
without neurofibromatosis. Similar findings—hyperintense pseudarthrosis
(arrow) with thickened hyperintense periosteum
(arrowheads)—can be seen on contrast-enhanced fat-suppressed
T1-weighted MR image (550/20). Histologic finding was that lesion was
chondroid tissue.
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In both patients with type IV pseudarthrosis, the osseous discontinuity was
clearly depicted on MR images. On T1-weighted images, the adjacent bone was
hypointense, thinned, and tapering. The pseudarthrosis appeared as a
discontinuity of the tibia and was demarcated hypointense on T1-weighted
images with an increased signal intensity after administration of contrast
material and on fat-suppressed images (Fig.
4A,4B,4C,4D).
The severe anterior bowing of the tibia in one of the patients with type IV
pseudarthrosis led to a marked thinning of the adjacent soft tissue in the
anterior part of the tibia. Thus, the bone was covered by only a thin fibrous
tissue layer and the skin. These findings correlated well with the
conventional radiographs and the operative findings.
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Fig. 4A. —5-year-old boy with neurofibromatosis and congenital tibial
pseudarthrosis (Crawford [6]
type IV). Lateral radiograph of right leg depicts congenital tibial
pseudarthrosis type IV with frank pseudarthrosis of distal tibia.
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Fig. 4B. —5-year-old boy with neurofibromatosis and congenital tibial
pseudarthrosis (Crawford [6]
type IV). On T2-weighted fat-suppressed selective presaturation inversion
recovery image (TR/TE, 4100/20), pseudarthrosis is revealed as tibial nonunion
with increased signal intensity (arrowheads) and hyperintense tissue
ventral to nonunion (arrows).
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Fig. 4C. —5-year-old boy with neurofibromatosis and congenital tibial
pseudarthrosis (Crawford [6]
type IV). T1-weighted MR image (550/20) show a hypointense pseudarthrosis area
with hypointense soft tissue ventral to pseudarthrosis (arrows).
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Fig. 4D. —5-year-old boy with neurofibromatosis and congenital tibial
pseudarthrosis (Crawford [6]
type IV). Pseudarthrosis and soft tissue (arrows) show marked
contrast enhancement after administration of gadolinium, corresponding to
hypercellular periosteum found at histologic examination.
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The periosteum in the area of the pseudarthrosis presented as a thickened
soft-tissue layer with hyperintense signal intensity on fat-suppressed and
T1-weighted contrast-enhanced images in all patients. This finding correlated
with the histologically confirmed thickening of the periosteum in the region
of the pseudarthrosis.
In the four patients with additional pseudarthrosis of the fibula, the area
of fibular nonunion was hyperintense on fat-suppressed and T2-weighted images.
The interposed soft tissue showed a hypointense signal and marked contrast
enhancement on T1-weighted images. Histologic specimens of the fibular lesions
were not available. Neurofibromas were not found in any of the patients.
Discussion
The cause of congenital pseudarthrosis of the tibia is unclear. A
coincidence with neurofibromatosis type I is a well-known fact, first
described in 1937 [7].
Neurofibromatosis was reported in 40% to 80% of patients suffering from
congenital pseudarthrosis of the tibia
[4,
7]. Local neurofibromas at the
location of the pseudarthrosis may be found, and Ippolito et al.
[8] discussed congenital
pseudarthrosis of the tibia as a possibly early or incomplete expression of
neurofibromatosis [9]. Fibrous
dysplasia and congenital ring syndrome also have been described in coincidence
with congenital tibial pseudarthrosis. A dominant autosomal trait associated
with hypoplastic fibula and pectus excavatum has been reported in one family
[10]. However, recent data on
genetic changes in patients with congenital tibial pseudarthrosis are missing.
Because this entity represents a complex disorder, different causal factors
seem likely to be responsible for the onset of this disease.
Three classifications of congenital tibial pseudarthrosis are commonly
used. The Andersen [11]
classification differentiates the morphology of the pseudarthrosis as
dysplastic, cystic, or sclerotic types, in addition to a clubfoot type that
arises because of accompanying abnormalities. Crawford
[6] described four types of
congenital tibial pseudarthrosis (Fig.
1). All types have in common an anterolateral bowing of the
affected tibia. In Crawford's type I, a continuous medullary canal and a
cortical thickening at the vertex of the bowing are found. Patients with this
type usually have a good prognosis; some may not even have a fracture. Type II
is defined by a constricted but continuous medullary canal with cortical
sclerosis. In type III, a cystic lesion is seen. Patients with this type of
pseudarthrosis tend to experience early fracture and, therefore, require early
treatment. Patients are classified as having type IV (Fig.
4A,4B,4C,4D)
if a discontinuity of the tibia is present at the initial imaging.
The classification of pseudarthrosis by Boyd
[12] consists of six types and
includes a type V, which is characterized by a complementary dysplastic fibula
and a type VI, in which an intraosseous neurofibroma or schwannoma is
evident.
A limitation of all classifications is the change of the disease morphology
caused by children's growth
[4]. However, determining the
type of the disease at initial imaging is most important for the
prognosis.
In our study, the typical morphologic features of the different types of
congenital pseudarthroses were clearly visible on MR images in each patient.
The MR findings corresponded to the findings seen on conventional radiographs.
The determination of the pseudarthrosis type of each patient was evaluated on
the basis of the Crawford [6]
classifications. MR imaging depicted the morphology of the pseudarthrosis and
the adjacent soft tissue more precisely than unenhanced radiography. In all
patients, the pseudarthrosis appeared hyperintense on fat-suppressed and
T2-weighted MR images. The images of patients with pseudarthroses of type I,
II, and IV showed a hypointense signal on T1-weighted images, whereas on those
of the child with type III, the pseudarthrosis appeared slightly hyperintense.
On contrast-enhanced T1-weighted images, a marked contrast enhancement was
visible. The extent of the lesion was clearly defined by the
contrast-enhancing area on T1-weighted images and the hyperintense areas on
fat-suppressed images. These findings correlated well with the extent of the
pseudarthrosis confirmed at surgery.
One major advantage of MR imaging was the depiction of the soft-tissue
abnormality adjacent to the pseudarthrosis. A typical finding was a local
thickening of the periosteum. The extent of periosteal thickening varied but
was clearly shown on the images of all patients. This finding was also
observed at surgery and confirmed in all histologic specimens. The periosteal
thickening extended further to the distal than to the proximal aspect of the
affected bone. In the patient with type I pseudarthrosis, the soft tissue
ventral to the tibia showed a diffuse edema on the STIR images corresponding
to a contrast enhancement on T1-weighted images. In our opinion, these
soft-tissue changes were caused by edema and cellular reaction attributable to
the physical strain generated by the tibial bowing.
Neurofibromatosis is a common finding in children with congenital
pseudarthrosis. The ability to detect deep soft-tissue neurofibromas is
another advantage of MR imaging in evaluating congenital pseudarthrosis.
Nevertheless, neurofibromas are rarely found at the site of pseudarthrosis.
Although Recklinghausen's disease was associated with the pseudoarthrosis in
four of our patients, neurofibromas were not evident at the site of
pseudarthrosis.
MR imaging of congenital pseudarthrosis provides valuable information on
the extent of the disease. Prognostic factors—such as the type of
pseudarthrosis, union or nonunion of the bone, and length and structure of the
pseudarthrosis area—can be derived from MR imaging. Because the
pseudarthrosis and affected periosteum must be removed completely, MR imaging
is helpful for the preoperative planning in that the borders for resection can
be defined precisely. Moreover, subtle soft-tissue changes can be accurately
evaluated with MR imaging. Thus, MR imaging can be recommended as an
additional imaging technique to be used with unenhanced radiography in the
diagnosis and follow-up of congenital pseudarthrosis of the tibia in pediatric
patients.
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Abstract
Introduction
