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DIAGNOSIS AVASCULAR NECROSIS OF THE FEMORAL HEAD
USING MR IMAGING NUCLEAR MEDICINE AND MEDICAL
RADIOLOGY DEPARTMENT
Farmonova Malika
Bukhara University of Innovative
Education and Medicine
Abstract
: Due to the pattern of its blood supply, the femoral head is
particularly vulnerable to avascular necrosis (AVN). Nontraumatic AVN is a
devastating disorder affecting young patients, and despite treatment it normally
follows a progressive course toward a destructive osteoarthropathy. Magnetic
resonance (MR) imaging is currently used in major classification systems solely
for early detection of femoral head AVN when plain radiographs are normal. More
recent data have shown that MR imaging may improve staging, investigate
radiologically occult collapse, depict other causes of disability and pain, assess
prognosis, and evaluate treatment. This article reviews the established and
evolving knowledge on MR imaging strategies and their role to visualize areas
and staging lesions of the hip joint with AVN of the femoral head.
Keywords: hip, osteonecrosis, avascular necrosis, radiation diagnostics.
Introduction:
The main clinical manifestations in the pathology of hip joints
are pain in the joint, in groin region with irradiation along the femoral nerve to the
knee joint and the gluteal region during physical exertion, sometimes night pains
also bother. Often, the pathology of the hip joint manifests itself in the form of
indistinct reflected pain in the knee joint. The smoothness of the contours of the
hip joint and soreness during palpation are objectively determined. Restriction of
rotational movements in the joint, abduction,reduction and flexion are also
limited, painful.
Magnetic resonance (MR) imaging is highly sensitive in depicting early AVN
and is considered the method of choice for accurate diagnosis and is staging of the
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disease. MR imaging can also assess severity and prognosis, depict the presence
of multiple foci of involvement, and guide and follow up the surgical treatment.
MR imaging is also used for the detection of minimal AVN lesions. This article
reviews the established and evolving knowledge on MR imaging strategies and
their role to visualize areas and staging lesions of the hip joint with AVN of the
femoral head.
Materials and methods:
The presence of a circumscribed subchondral
"bandlike" lesion with low signal intensity (SI) on Tl-weighted sequences is
considered pathognomonic of AVN. We can see "double-line" sign on non-fat-
suppressed T2-weighted SE and TSE images which is virtually diagnostic of
AVN. It occurs at the interface between viable and nonviable tissue and consists of
an outer low SI rim (suggested to represent reactive sclerotic bone) and an inner
high SI rim (considered to represent vascular granulation tissue and/or chondroid
metaplasia). Mitchell et al was first who described and found this sign in 85% of
AVN lesions. According to the SI of the region within the double line and based
on the chronological order of its appearance, Mitchell et al proposed a
classification system ranging from A (early stage, retaining normal fat SI) to D
(advanced stage, low SI due to fibrous tissue and sclerosis). This system has not
been used widely because it does not correlate with radiographic staging and
prognosis[10].
Besides its definite association with histopathological changes, the "double-
line" sign is considered to reflect a chemical shift artifact notified at the frequency
encoding direction axis of the field. Although the double-line sign has the
characteristics of an artifact, this does not alter its diagnostic significance.
Nowadays, there is widespread use of T2-weighted TSE sequences with spectral
fat saturation (to overcome the JJ-coupling effect that leads to bright fat) and thus,
the double-line sign is not seen but rather manifests as a "bright band-like" sign
evident also on contrast-enhanced Tl-weighted sequences. Subchondral fractures
in AVN typically occur as low SI lines on Tl-weighted MR images and can be
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differentiated from subchondral insufficiency fractures in osteoporotic women
based on the shape of the lesion: In AVN, the low SI band is smooth, concave to
articular surface, and circumscribes all of the necrotic segment, whereas in
insufficiency fractures the low SI band is irregular, discontinuous, and convex to
the articular surface. On T2-weighted SE MR images, subchondral fractures may
have a variable SI because the fracture may be filled by gas or fluid. MR imaging
has been found to be less sensitive than computed tomography (CT) in detecting
subchondral fractures in AVN: Extension of the fracture line through the cortex in
CT is seen in 70% of patients who do not show any evidence of fracture with MR.
In our experience (unpublished data), modern MR scanners in the appropriate
protocol setting including unilateral two-dimensional and/or three-dimensional
high-resolution images, are able to demonstrate the subchondral fracture equally
or even better than CT, the latter being limited from the radiation it induces. Joint
effusion, probably secondary to AVN-related synovitis, is seen in 62 to 80% of
patients with AVN regardless of the presence of articular collapse. Joint effusion
is usually found in association with bone marrow edema and is more common
(94%) in advanced disease.
MR imaging has been shown to be more sensitive than CT or scintigraphy
for early detection of AVN in patients with normal radiographs (stage I).The
reported sensitivity of MRI for early diagnosis of AVN ranges between 86% and
100% compared with 83% of radionuchde scintigraphy. In one study, MR imaging
detected AVN in 30% of hips in the preradiological stage (stage 1). In another
study it was found that 90% of asymptomatic and radiographical normal hips had
early stage focal lesions evident on MR imaging. Even limited MR imaging
protocols can effectively diagnose the presence and quantify the size of MR
imaging can also be helpful for the prediction and early detection of AVN in
patients with predisposing factors, such as hip trauma. MR studies can detect
signs suggesting AVN in up to 60% of patients at 3 months following simple hip
dislocation. MR imaging with and without contrast is suggested in the follow-up
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of hip dislocation in patients with worsening of pain upon resumption of normal
activities. Dynamic MRI has been shown to be highly reliable in the evaluation of
femoral head vascularity and progression to AVN after intracapsular femoral neck
fracture. Preliminary studies have shown that proton MR spectroscopy can detect
changes in the lipid/water spectra of patients at risk of AVN before any
morphological changes are evident, thus suggesting a potential role of this
technique in predicting the risk of developing AVN. Increased diffusion of water
protons has been also found in hips with AVN compared with normal hips. Proton
MR spectroscopy and diffusion-weighted imaging (DWI) are not yet in routine
use for musculoskeletal imaging, and thus their role for early detection of AVN
remains to be clarified.
MR is currently an integral part of several staging systems and has been used
as a separate tool for lesion classification and lesion size quantification. There are
various grading and classification systems incorporating a variety of methods for
lesion quantification because there is no agreement yet on a single universal
system. However, the most frequently used systems are those from University of
Pennsylvania (Steinberg's) and the Association Research Circulation Osseous
(ARCO) classification. The first classification system to incorporate MR was that
of the University of Pennsylvania. The stage in this system is determined initially
according to the changes seen on radiography and MR and then based on
measurements of lesion size and articular surface involvement. Later, for
simplification reasons, stages II and IV and stages V and VI were combined to
provide a total of five rather than seven stages (ARCO international classification
system). The most critical point in all the classification systems is the loss of
spherical contour of the femoral head. Although MR is used at the early
precollapse stages, only radiographs are employed routinely for the evaluation of
collapse, and MR is used only in the precollapse stages. It has been shown that
plain radiographs can miss important information in stages II and III, because they
overestimate stage II, underestimate stage III lesions, and are inaccurate in
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estimating the collapse size, which is an important parameter in therapeutic
decisions (Figs. 1 and 2).
Figure 1.
Radiographic understaging of femoral head osteonecrosis. (A)
Frog plain radiograph shows sclerosis and lysis in
a symptomatic patient, with intact femoral head suggesting a stage ARCO II
disease. The contrast-enhanced fat-suppressed
Tl-weighted magnetic resonance images in the (B) sagittal and (C) oblique
axial planes confirm the presence of the
osteonecrotic lesion (thin arrows) and in addition show bone marrow edema
(open arrows). It is only the oblique axial image,
which in addition shows a focal flattening of the femoral head (arrowhead,
C), thus upgrading the stage to IIIA.
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Figure 2.
A 51-year-old male patient with a history of carcinoma of the
larynx and corticosteroid administration. The patient
was referred for magnetic resonance (MR) imaging because of a persistent
pain for the last 3 months over the left hip and joint
movement restriction. (A) Plain radiograph shows osteosclerosis (arrows)
typical for avascular necrosis (AVN) of the femoral
head (stage ARCO II). (B) Coronal Tl-weighted MR image confirms the
presence of AVN (arrow). (C) Oblique axial fatsuppressed
contrast-enhanced high-resolution Tl-weighted MR image shows depression
of the articular surface (open arrows).
This finding upgrades the stage to ARCO NIA. There is also bone marrow
edema secondary to the articular collapse (arrows).
Therefore it has been suggested that the wider use of MR imaging findings in
any classification system could improve the accuracy and prognostic value by
means of discriminating between early and advanced stages. Others found that
MR is less sensitive than CT in detecting subchondral fractures (stage III disease).
This remains to be confirmed by additional studies.
Conclusion:
1. The leading method of diagnosis of AN, in particular, in the early stages of
the disease, is MRI tomography, which allows you to determine the presence of a
pathological process, its size and localization, tactics and scope of surgical
intervention, as well as to evaluate its effectiveness.
2. One of the early MRI signs of AN is edema and necrosis of the bone
cuticle.
3. MR is currently an integral part of several staging systems and has been
used as a separate tool for lesion classification and lesion size quantification.
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