AJR 2003; 181:1590-1592
© American Roentgen Ray Society
Juxtacortical Glomus Tumor of the Distal Femur Adjacent to the Popliteal Fossa
Fergus J. Perks1,
Ian Beggs1,
Graham M. Lawson2 and
Ron Davie3
1 Department of Radiology, Royal Infirmary of Edinburgh, 51 Little France
Crescent, Edinburgh EH16 4SA, United Kingdom.
2 Department of Surgery, St. John's Hospital, Livingston EH546PP, United
Kingdom.
3 Department of Pathology, St. John's Hospital, Livingston EH546PP, United
Kingdom.
Received February 12, 2003;
accepted after revision April 29, 2003.
Address correspondence to I. Beggs.
Introduction
Glomus tumor is a benign neoplastic proliferation of modified smooth muscle
cells. The lesion characteristically occurs in a digital subungal location and
presents with well-localized pain that is exacerbated by temperature change.
Typical sonographic and MRI features have been documented. Extradigital glomus
tumors have also been described and can be difficult to diagnose
preoperatively. We present a case of histologically proven glomus tumor in a
previously unrecognized site with atypical MRI findings.
Case Report
A 37-year-old woman presented with worsening episodes of lancinating
posterolateral left knee pain. The knee had been painful and stiff for several
years. Symptoms were exacerbated by activity. There was no history of injury.
Physiotherapy and nonsteroidal antiinflammatory medication had no effect.
On examination, the patient had an antalgic gait, block to full knee
extension, and extreme tenderness on palpation at the lateral margin of the
popliteal fossa. There was no distal neurovascular deficit.
The initial MRI showed a well-defined mass isointense relative to muscle on
T1-weighted spin-echo images (Fig.
1A) and hyperintense on proton density–weighted images. The
mass was hyperintense and surrounded by diffuse high signal on fat-saturated
T2-weighted (Fig. 1B) and
gradient-echo images. The adjacent femoral cortex was normal.
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Fig. 1A. —37-year-old woman with popliteal fossa glomus tumor. Axial
T1-weighted image (TR/TE, 750/11) shows mass (arrow) isointense
relative to muscle and ill-defined hypointense perilesional signal extending
to popliteal vessels.
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Fig. 1B. —37-year-old woman with popliteal fossa glomus tumor. Coronal
T2-weighted image (4,000/102) obtained with fat saturation shows high-signal
popliteal fossa mass with surrounding irregular high signal and several
prominent perilesional vessels.
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An MRI obtained 4 months later showed that the mass was unchanged and the
perilesional high signal had largely resolved
(Fig. 1C). The coronal
T2-weighted sequence showed several small vessels running into or adjacent to
the tumor (Fig. 1C). After IV
injection of gadolinium, the mass enhanced homogeneously except for a 2-mm
central region (Fig. 1D).
Findings of radiography were normal. Sonography showed that the mass was solid
and hypoechoic. No color-flow or Doppler signal was present
(Fig. 1E).
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Fig. 1C. —37-year-old woman with popliteal fossa glomus tumor. Coronal
T2-weighted image (4,000/112) obtained with fat saturation 4 months after
initial MRI shows resolution of adjacent abnormal signal. Small vessel runs
into mass superiorly.
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Fig. 1D. —37-year-old woman with popliteal fossa glomus tumor. Axial
gadolinium-enhanced T1-weighted image (750/14) obtained 4 months after initial
MRI shows enhancing mass with focal area of nonenhancement due to fibrosis
(arrow).
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The popliteal fossa was explored under tourniquet control. No abnormality
of the tibial or common peroneal nerves was identified. Dissection under loupe
magnification revealed a 15 x 8 mm bean-shaped lesion that was adherent
to the posterior surface of the lateral femoral condyle and branches of the
superior lateral genicular nerve and that appeared to arise from the wall of a
tributary of the lateral superior genicular vein. The lesion was excised.
Postoperatively, the patient experienced almost instant relief from pain and
was able to extend her knee fully.
Histologic examination revealed a benign circumscribed and thinly
encapsulated mass typical of a solid-type glomus tumor with sheets of glomus
cells containing sparse small blood vessels
(Fig. 1F). The glomus cells
showed positive staining for smooth-muscle actin. Larger thin-walled vessels
were present centrally, similar to those seen in a glomangioma. A central 2-mm
focus of fibrosis was present, with evidence of previous internal hemorrhage
(Fig. 1G).
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Fig. 1G. —37-year-old woman with popliteal fossa glomus tumor.
Photomicrograph of histopathologic specimen shows area of fibrosis (short
arrows), lymphocytes, and hemosiderin deposits (long arrow)
suggesting previous hemorrhage adjacent to vessel. (H and E, x100)
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Discussion
Glomus bodies lie in the stratum reticularis of the dermis and are
particularly numerous in the digits, palms, and soles of the feet. They are
composed of an afferent arteriole, an arteriovenous complex with a
neurovascular reticulum, and efferent venules. The specialized glomus cells
regulate arteriolar flow and temperature. Neoplastic growth produces the
glomus tumor. Histologic examination reveals branching vascular channels
separated by connective tissue stroma containing aggregates, nests, and masses
of specialized glomus cells that have electron microscopic features of
smooth-muscle cells [1]. Glomus
tumors are most often of the solid type, but vascular and myxoid types also
occur.
Up to 35% of glomus tumors are extradigital. Sites around the knee include
the femoral metaphysis, suprapatellar subcutaneous tissue within the joint
capsule, the patellar ligament, and the Hoffa fat pad. Two cases in the
popliteal fossa, both superficial
[2,
3], and a case of periosteal
glomus tumor adjacent to the lateral femoral metaphysis have been described
[4]. The classic clinical
features of well-localized pain and cold sensitivity may not be present in
extradigital sites, as in this case, and the histology may be
uncharacteristic, tending to be of the vascular type. Preoperative diagnosis
can be difficult.
Most descriptions of the imaging findings of a glomus tumor refer to a
subungal location [5], although
extradigital lesions have broadly similar imaging characteristics. Sonography
shows an encapsulated mass with a smooth or lobulated outline
[6,
7]. MRI shows low signal on
T1-weighted images, high signal in T2-weighted images and gradient-echo
images, and homogeneous gadolinium enhancement. To our knowledge proton
density–weighted imaging findings have not been described.
The imaging findings in this case are consistent with previous studies of
digital and extradigital glomus tumor. However, we described two previously
undocumented features, localized perilesional high signal on T2-weighted and
gradient–echo sequences and incomplete enhancement on
gadolinium-enhanced sequences. The perilesional high signal intensity without
a history of trauma may have been caused by spontaneous hemorrhage, given the
vascular nature of glomus tumors and the histologic evidence of previous
hemorrhage within the mass. Increased vascularity surrounding glomus tumors is
not rare [8] and has been seen
on sonography [7]. Soft-tissue
hemorrhage can be associated with other soft-tissue tumors, particularly
malignant fibrous histiocytoma, but this is rarely seen in lesions smaller
than 1.5 cm. The abnormal signal had resolved on the second MRI, consistent
with hemorrhage. To our knowledge, foci of nonenhancement on contrast-enhanced
MRIs have not previously been described in glomus tumors. Histologic
examination in this case showed that the area of nonenhancement was due to
intralesional fibrosis.
The broad differential diagnosis includes neural tumor, in particular a
localized neurofibroma; vascular tumor, including hemangioma, angioma, or
hemangiopericytoma; and leiomyoma or metastasis.
We described a histologically proven juxtacortical glomus tumor of the
distal femur adjacent to the popliteal fossa. Presurgical sonography and MRI
depicted lesion characteristics and location. Glomus tumor should be
considered in the differential diagnosis of any small enhancing soft-tissue
mass. Incomplete enhancement due to internal fibrosis and perilesional high
signal due to hemorrhage may be features.
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Introduction
Case Report
