AJR 2005; 185:394-396
© American Roentgen Ray Society
Resorption of Osteochondroma by Accompanying Pseudoaneurysm
Ja-Young Choi1,
Sung Hwan Hong1,
Han-Soo Kim2,
Chong Bum Chang2,
Young Joon Lee3 and
Heung Sik Kang1
1 Department of Radiology, Seoul National University College of Medicine and
Institute of Radiation Medicine, 28 Yongon-dong, Chongno-gu, Seoul
110–744, Korea.
2 Department of Orthopedics, Seoul National University College of Medicine,
Seoul 110–744, Korea.
3 Department of Radiology, Pusan-Paik Hospital College of Medicine, Inje
University, Pusan, Korea.
Received June 23, 2004;
accepted after revision September 22, 2004.
Address correspondence to S. H. Hong
(hongsh{at}radiol.snu.ac.kr).
Introduction
Osteochondromas are the most common benign tumors of the bone, appearing
during the growth period [1].
Vascular complications associated with osteochondroma include vessel
displacement, stenosis, occlusion, and pseudoaneurysm formation
[2], among which pseudoaneurysm
is the most common. No cases with disappearance of osteochondroma resulting
from accompanying pseudoaneurysm have been reported. We report a case of
pseudoaneurysm associated with osteochondroma and resorption of the original
tumor caused by a progressively enlarged pseudoaneurysm.
Case Report
A 12-year-old boy presented with painful swelling in the left popliteal
fossa. It was a sudden onset without prior trauma. A plain radiograph showed a
broad-based exophytic bone lesion in the distal femur that had continuity with
the medullary cavity, suggesting sessile osteochondroma
(Fig. 1A). The MR image showed
no cartilage cap but a small, dark signal-intensity lesion posterior to the
skeletal stalk was present, accompanied by pulsation artifacts
(Fig. 1B). At first, the boy
was treated only with antiinflammatory drugs and the pain was rapidly
relieved, but the swelling gradually increased. Two months later, a follow-up
plain radiograph showed that the stalk had nearly disappeared, but that a
huge, well-defined soft-tissue mass had developed in the distal thigh
(Fig. 1C). An MRI examination
revealed a large, partially thrombosed pseudoaneurysm with severe pulsation
artifacts (Fig. 1D). This
diagnosis was confirmed by a Doppler sonography examination
(Fig. 1E). CT angiography
showed the objective relationship between the parent artery and aneurysmal
neck (Fig. 1F). Surgery
revealed the presence of a 10 x 13 cm thrombosed pseudoaneurysm
originating from the popliteal artery in the popliteal fossa. However, no
evidence of residual osteochondroma was present. Removal of the pseudoaneurysm
and autologous venous patch angioplasty were then performed.
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Fig. 1B —12-year-old boy with swelling and pain in left popliteal
fossa. Axial fat-suppressed enhanced MR image (TR/TE, 500/16) shows lesion
with dark signal intensity (open arrow) posterior to osteochondroma
(arrow). Dark lesion is accompanied by pulsation artifacts
(arrowheads).
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Fig. 1C —12-year-old boy with swelling and pain in left popliteal
fossa. Two months later, follow-up plain radiograph shows markedly shortened
stalk (arrow). Huge, well-defined soft-tissue mass
(arrowheads) is seen in distal thigh.
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Fig. 1D —12-year-old boy with swelling and pain in left popliteal
fossa. Sagittal T2-weighted MR image (TR/TE, 4,000/85) shows large
pseudoaneurysm with concentric layers (arrows) of alternate high and
low signals, suggestive of mural thrombosis. Signal void area
(asterisk) is from turbulent flow within lumen. Severe pulsation
artifacts (arrowheads) are associated with it.
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Fig. 1E —12-year-old boy with swelling and pain in left popliteal
fossa. Duplex color Doppler sonogram of pseudoaneurysm reveals characteristic
red and blue flow pattern, suggestive of turbulent flow.
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Fig. 1F —12-year-old boy with swelling and pain in left popliteal
fossa. CT angiography with sagittal reformation shows short aneurysmal neck
(arrows) between popliteal artery and pseudoaneurysm. Pseudoaneurysm
partially enhances because of mural thrombus (asterisk).
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Discussion
Pseudoaneurysm formation associated with osteochondroma is by far the most
common vascular complication. It typically occurs near or after skeletal
maturity as the soft cartilage cap becomes hardened by calcification or
ossification, and hence can cause increasing damage to the adjacent vessel
[3]. Osteochondromas lying
adjacent to an artery can chronically abrade and, ultimately, lacerate the
arterial surface with normal movement or repetitive trauma. In our case, the
osteochondroma did not have the cartilage cap on initial MR images. We think
that the soft cartilage cap of the tumor was prematurely ossified, and, as a
result, the hardened tumor caused the pseudoaneurysm. The predominance of
popliteal artery involvement of the pseudoaneurysm is related to the frequency
of osteochondromas in this location and to the fixed position of this vessel
proximally at the adductor aponeurotic hiatus and distally by the geniculate
branches [4]. This lack of
mobility of the popliteal artery prevents the vessel from displacing, but it
instead becomes tethered over the osteochondroma
[2]. Most pseudoaneurysms are
associated with sessile osteochondromas, which are more likely to exert
chronic friction on the vessel than pedunculated osteochondromas that simply
displace the vessel [5].
Pseudoaneurysm can be confirmed by sonography, conventional angiography,
contrast-enhanced CT, or MRI. MRI plays an important role in differentiating
pseudoaneurysms and tumors. In pseudoaneurysms, MRI characteristics include
pulsation artifacts and the low-signal onionlike laminar structures on
T1-weighted and T2-weighted images due to the deposition of hemosiderin
peripherally and thrombus of different degrees
[5]. It can be difficult to
detect a pseudoaneurysm if it is small and asymptomatic. In such a case, an
MRI can be helpful for diagnosis because pulsation artifacts from the arterial
pulsation of the pseudoaneurysm can be easily detected despite its small size,
as in our case.
Interestingly, regression or resorption of an osteochondroma occurring both
spontaneously and after a fracture has been reported
[6–8].
The suggested mechanism of spontaneous regression or resolution of an
osteochondroma is the cessation of growth followed by active resorption and
metaphyseal remodeling [9].
However, we think that the osteochondroma in our case had initially induced
the pseudoaneurysm, which was progressively enlarged and caused pressure
erosion on the original tumor, and consequently, the tumor has nearly
disappeared.
In conclusion, we have described a case of an osteochondroma that has
nearly resorbed as a result of the accompanying pseudoaneurysm.
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Introduction
Case Report
