S. E. Anderson, PhD
Institute of Diagnostic, Interventional and Pediatric Radiology, University Hospital, Inselspital, Freiburgstrasse, 3010 Bern, Switzerland
A. M. Davies, MD
Consultant Radiologist, The MRI Centre, Royal Orthopedic Hospital NHS Trust, Bristol Road, Birmingham, B31 2AP, UK
Pseudotumors in Sports 8
Suzanne E. Anderson and A. Mark Davies
Box 8.1. Plain radiography/CT
Imaging technique of choice for evaluation of:
● (Mature) myositis ossifi cans
● Calcifi cations
● Radiopake foreign bodies
● Evaluation of acute or chronic avulsion fractures
Box 8.2. MR Imaging
● Imaging in three planes required
● Imaging protocol should include at least T1-WI and STIR or fat suppressed T2-WI
● Gradient echo imaging: useful to detect hemo- siderin, metallic foreign bodies and gas
● Should always be correlated with clinical history and plain fi lms/CT
8.1
Introduction
In many instances it will be clear that an apparent clinical mass is directly due to a specifi c sporting injury, such as a thigh hematoma after direct impac- tion during football. Commonly the sports person is fully aware of the injury and relationship with the development of the mass or abnormal region and many sports activities are associated with specifi c injuries and fi ndings. However sports injuries may
C O N T E N T S
8.1 Introduction 103 8.2 Imaging Principles 104
8.3 Keys to Differential Diagnosis and True Tumors 105
8.4 Myositis Ossifi cans 105 8.5 Infl ammatory Myopathies 106 8.6 Nodular Fasciitis or
Pseudosarcomatous Fasciitis 106 8.7 Tears and Overuse of
Ligaments and Muscles 106 8.8 Stress Reactions and Fractures 107 8.9 Muscle Abnormalities, Partial and
Full Thickness Tears and Hematomas 108 8.10 Infection 110
8.11 Normal Variants 111
8.12 Calcium Deposition Disorders 112 8.13 Metabolic Disorders 113
8.14 Foreign Body Reactions 114 8.15 Vascular Pseudoaneurysms 114
8.16 Post Treatment/Intervention and Others 114 8.17 Rheumatological or
Degenerative Joint Disease 114 8.18 AVN and Transient Osteoporosis 114 8.19 Muscle Denervation 116
Things to Remember 117 References 117
be minor and forgotten and not immediately per- ceived as being related to the current clinical prob- lem, or if acute maybe be associated with unusual radiological fi ndings confusing the diagnosis or be related to chronic overuse. This insult may then be complicated by secondary infection. Contributory features include the presence of normal variants with overuse syndromes, body habitus and inap- propriate training and equipment or overwork. In other cases, characteristic locations and patient age may be suggestive of the diagnosis, such as elastofi broma dorsi of the infra-scapular posterior thoracic wall.
Musculoskeletal pseudotumors on MRI are not infrequent and may be due to an increased avail- ability of MRI and expanding clinical referral basis.
A large variety of MRI pseudotumors exist.
There are two types of pseudotumors. First, clini- cal ones, i.e. those patients who present with fi ndings of a mass or swelling suggestive of a tumor. Second, an apparent tumor evident on imaging in which patients present with imaging fi ndings mistaken for a tumor. Pseudotumors are far more common than true tumors. They can be classifi ed either anatomi- cally or by etiology. All anatomical structures may be involved.
8.2
Imaging Principles
All modalities are involved in pseudotumor imaging.
Often the radiologist does not have a choice, as imag- ing has already been performed before the patient presents. When radiology can infl uence the simple imaging choices, remaining with basic principles is always prudent. Radiographs in two planes are help- ful – to review for example any calcifi cation, zoning phenomena, fracture, or for the presence of normal variants or overuse such as advanced degenerative joint disease ill fi tting with age. Computed tomog- raphy can help with clarifying the above and MRI is a main stay with sports pseudotumors given its multiplanar capability, regional anatomical review, and capacity to review all anatomical structures.
Regarding MRI, routine sequences in three planes are important. Ensure T1 and T2-weighting and STIR (Short Tau Inversion Recovery) in at least one plane.
Gradient echo sequences may be useful to enhance a “blooming” artefact associated with hemosiderin
deposition, metallic foreign bodies and gas. Though contrast administration may not necessarily change the diagnosis, it may increase conspicuity of fi nd- ings, differentiate between solid and cystic masses and has been shown to be of use with professional athletes where muscle strains may be negative on T2-weighting.
Improved MRI diagnosis for pseudotumor is pos- sible with increased awareness by the radiologist to the imaging appearances of commoner types of pseudotumors, by correlation with radiographs and by obtaining an appropriate clinical history. Either with the use of a small questionnaire before MRI or quick check by the reporting radiologist with brief review of the patient’s clinical history and clinical appearance, the MRI diagnosis may be quite specifi c.
Often this diagnosis may be a surprise to the refer- ring clinician.
Correlation with conventional radiographs is extremely important as many masses or focal abnor- malities on MRI simulating neoplasms may have characteristic radiographic appearances and be easily diagnosed (Jelinek and Kransdorf 1995;
Kransdorf and Murphey 1997). Examples include the peripheral calcifi c rim of myositis ossifi cans, retained radio-opaque foreign bodies, stress frac- ture of bone and hydroxyapatite deposition within tendons.
Fat necrosis, muscle hematoma and myositis ossi- fi cans of muscle may give rise to MRI pseudotumors.
Fat necrosis after minor trauma may result in a clini- cally palpable mass. Only one quarter of children with an MRI fat necrosis pseudotumor recalled a history of trauma (Tsai et al. 1997). On MRI there was linear signal intensity within the subcutaneous tissues of either the anterior tibia or of the buttock region, an absence of a mass, though there was commonly a volume plus of the subcutaneous region (Tsai et al. 1997).
On MRI if there is an absence of a true mass, and a fi nding associated with a large reactive soft tissue component or hemorrhage, and there has been a history of sports injury, trauma or overuse, then at least an MRI pseudotumor should be included in the differential diagnosis. If after review of the imaging appearances, particularly with MRI and radiographs, attention is paid to the clinical and history details, then sometimes a biopsy may not be needed. It is always prudent to have routine clinical and imag- ing follow-up after suggesting a pseudotumor diag- nosis particularly when early on the learning curve for these abnormalities. It will decrease the surprise element.
8.3
Keys to Differential Diagnosis and True Tumors
Typically true musculoskeletal tumors of either bone or soft tissues present with an increasing mass effect and relatively minor pain compared to the mass size, unless there has been a history of bleeding, biopsy or accident. Radiologically with a true tumor there is commonly a mass lesion, which is displacing or invading local anatomy. Usually with pseudotumors, there is an absence of a genuine mass lesion, with more often a lack of an anatomical structure, making comparison with the contralateral side helpful and also imperative in some circumstances. Pseudotu- mors are very commonly associated with a marked adjacent tissue reaction, as classically seen with myo-
sitis ossifi cans. Adjacent marked reactive soft tissue change or hemorrhage is extremely unusual with a true tumor unless there has been a history of direct trauma, bleeding or biopsy.
8.4
Myositis Ossifi cans
Localized myositis ossifi cans is a common MRI pseu- dotumor (Fig. 8.1) (Boutin et al. 2002). Usually the heterotopic formation of bone occurs within muscle and in approximately one quarter of cases due to an identifi ed trauma. It may rarely occur in asso- ciation with other structures such as tendons and fascia. During the active initial phase the mass-like
Fig. 8.1a–c. Sixty-year-old male with lower limb mass – inter- mediate phase of myositis ossifi cans. a Axial T-1 weighted fat suppressed post contrast enhanced MR image with “tide mark sign” (arrow) representing the beginning of the peripheral rim of calcifi cation. b Adjacent axial image, shows marked soft tissue reaction (thick arrows) and perifascial fl uid (thin black arrow) commonly associated with myositis ossifi cans, which would be most unlikely to be seen with a true tumor unless after trauma or biopsy with hemorrhage. c Hematoxy- lin and eosin stained histology showing peripheral zone ossi- fi cation, typical for myositis ossifi cans. (Pathology courtesy of Edouard Stauffer)
a
c
b
region may be clinically warm, painful and woody in consistency. Biopsy during the early phase of devel- opment may give a false osteosarcoma diagnosis, as there is fl orid osteoblastic activity. Serial radiographs demonstrate the development of a peripheral rim of calcifi cation of the mass at usually six to eight weeks after injury and that the calcifi cation is separate from bone. If the trauma involves deep muscle injury in some cases there may be an associated periosteal reaction of the adjacent bone, referred to as periostitis ossifi cans. The appearances on MRI refl ect the phase of development of the myositis ossifi cans and the zone phenomenon of the histology. In the early phase before ossifi cation the lesion is usually isointense to muscle on T1-weighting with no distinct borders and increased in signal intensity on T2-weighting cen- trally (De Smet et al. 1992), with marked adjacent soft tissue edema. At this stage there may or may not be a subtle peripheral rim, like a tidemark. In sub- acute lesions with early peripheral calcifi cation there is a low signal intensity rim, like a tidemark on the beach when the wave is residing, refl ecting this cal- cifi cation. The center of the lesion may be isointense to muscle or slightly increased in signal intensity on T1-weighting. On T2-weighting the central portion of the lesion is very high in signal intensity and the rim’s decreased signal is more clearly evident (Jelinek and Kransdorf 1995; De Smet et al. 1992). At this sub- acute stage the adjacent edema of soft tissues may be very prominent. A common feature to myositis ossifi cans in the acute and subacute phases is the marked adjacent soft tissue reaction, which is very unusual in primary malignant tumors, which have not been previously biopsied or undergone intratu- moral hemorrhage (Jelinek and Kransdorf 1995).
In the chronic phase, the central portion of the lesion is slowly ossifying, so eventually the signal intensity is similar on T1- and T2-weighting to that of fatty marrow of bone (De Smet et al. 1992). It should be stressed that maturation on radiographs and CT is a good discriminator of this condition from min- eralising real soft tissue sarcomas such as synovial sarcoma and soft tissue osteosarcoma. Though less common, multiple muscles and the regions between muscles may be involved. A variant of myositis ossi- fi cans occurring in the fi ngers and less commonly in the toes is fi bro-osseous pseudotumor of the digits or fl orid reactive periostitis.
8.5
Infl ammatory Myopathies
Infl ammatory myopathies are most usually diffuse in nature, commonly bilateral in the thighs or calves and associated with weakness or tiredness, though quite rare some forms may be focal such as nodular myositis, sarcoid associated myopathy (Fujimoto et al. 2002) and diabetic muscle infarction. They may occur in sporting individuals and are often fi nally diagnosed with histology.
8.6
Nodular Fasciitis or
Pseudosarcomatous Fasciitis
Nodular fasciitis or pseudosarcomatous fasciitis commonly occurs in 20–35 year old athletic patients presenting with a focal clinical mass with pain. There are three forms: subcutaneous the commonest, intra- muscular which may appear as a focal mass and MRI pseudotumor, and fascial which usually spreads along superfi cial fascial planes. Early lesions typically have a high T2 signal intensity refl ecting the myxoid his- tology (Jelinek and Kransdorf 1995; Kransdorf and Murphey 1997) and older lesions may have more decreased signal intensity on T2-weighting refl ecting the more predominantly fi brous histology (Jelinek and Kransdorf 1995). Overall the MRI appearance is non-specifi c.
8.7
Tears and Overuse of Ligaments and Muscles
Tears and overuse of ligaments and muscles, both acute and chronic, may cause MRI pseudotumors. Partial avulsion of the adductor muscles of the thigh from the femoral diaphysis in children due to sports injuries or overuse may cause an MRI pseudotumor, which may simulate a malignant sarcoma ( Anderson et al. 2001).
In fi ve young patients, who presented with a provi- sional clinical and radiological diagnosis of femoral sarcoma, review of MRI from three patients showed a periosteal reaction on the posteromedial aspect of
the femur centered on the muscle-bone interface of the vastus medialis and intermedius and adductor muscle insertions on the femoral shaft (Charkes et al. 1987).
There was widespread intramedullary edema and an absence of bone or soft tissue mass. Stress fractures lines were excluded. This condition has been studied using bone scans in adults, in army training and called
“adductor insertion avulsion syndrome” or “thigh splints”. The cause is thought to be due to excessive adductor contraction with stripping of the femoral periosteum posteromedially. Knowledge, particularly of the MRI fi ndings with an appropriate clinical set- ting can help physicians to make the correct diagnosis and eliminate unnecessary biopsy. Proximal adductor avulsions near the symphysis pubis (Schneider et al.
1976) and intramuscular strains (Yoshioka et al. 1994) have been described in adults. Chronic muscle avulsive injuries in a variety of lower limb sites in children have been described (Donnelly et al. 1999; Anderson et al. 2004a). Overuse with excessive prolonged carrying of large babies may rarely lead to masses of the wrist, found to be due to de Quervains tenosynovitis.
8.8
Stress Reactions and Fractures
Post-traumatic bony abnormalities such as stress reactions and fractures may cause MRI pseudotumors.
Many sporting activities are associated with common sites and patterns (Figs. 8.2 and 8.3) (Pavlov 1995), such as junction of pelvis and ischium in long dis- tance runners, and hook of hamate in golf and tennis players. In the clinical history review for altered or excessive training and changed equipment may be helpful. Excessive training with suboptimal shoes in fi gure ice skaters and professional snow boarders may cause MRI pseudotumors of soft tissues around the ankle associated with the shoe rim (Anderson et al. 2004b). Some sites for stress fractures are prac- tically pathognomonic for specifi c sports such as spinal pars defects of the thoracic and lower lumbar spine in cricketers particularly in fast spin bowlers with unilateral defects often involving the side oppo- site to the bowling arm (Fig. 8.4) (Hardcastle et al.
1992). Fortunately these are now rare due to aware- ness and change of training. Any periosteal reac- tion associated with muscle hypertrophy in a sports person should prompt review of type of training and accurate history of pain, as the MRI fi ndings may be
due to overuse. Radiographic correlation and follow- up are important. Any linear low signal intensity on T1-weighting associated with increased signal inten- sity of T2-weighting (Fig. 8.5), which becomes more obvious with contrast enhancement and fat suppres- sion should prompt a diagnosis of stress fracture.
Radiographic and clinical correlation and follow-up are important.
Stress reactions and fractures is the largest area where stress/trauma-related lesions on imaging are mistaken for sarcomas. Stress fractures in the imma- ture skeleton are frequently mistaken for sarcomas
Fig. 8.2. Young male soccer player with left sided symphyseal stress reaction (arrow) and adductor strain on an axial STIR image
Fig. 8.3. Young female professional snow boarder with distal fi bular stress reaction (arrow) on axial T1-weighted fat sup- pressed MR image after contrast administration, performed as part of a routine tumor work-up MR protocol
on imaging (particularly the proximal tibia and distal femur). If the correct diagnosis is not made on conventional radiographs, and the clinical problem is followed with imaging modalities, notably MRI, a
large number of pseudotumor appearances may be displayed, and compounds the diagnostic error. This may lead to unnecessary biopsies and also to errors in pathology results.
Acute or chronic stress avulsion injuries in the immature skeleton, particularly acute-on-chronic traumatic avulsions (Fig. 8.6), not uncommonly may simulate bone forming surface lesion tumors or intraosseous sarcomas. These are a particular prob- lem around the pelvis and may be compounded by the presence of normal variation in synchondroses Donnelly et al. 1999).
8.9
Muscle Abnormalities, Partial and Full Thickness Tears and Hematomas
Muscle abnormalities and tears (Fig. 8.7) (May et al. 2000), soft tissue hematomas, abscess formation and ischemic-compression syndromes are common MRI pseudotumors. Superfi cial soft tissue hemato- mas may be associated with minimal trauma and the event little thought of at the time of presentation to MRI. Whereas deep muscle hematomas are more commonly associated with more obvious trauma, coagulation disorders such as hemophilia or diffi -
Fig. 8.4.a Fast spin bowler in action after a hat trick, represent- ing Australia against Pakistan. b Sagittal T1-weighted fat sup- pressed MR image depicting L3 and L4 left sided pars inter- articularis stress reaction (arrows). (Case and images courtesy of Anthony Stuart)
a b
Fig. 8.5a,b. Sixty-year-old female with known osteoporosis, and ankle pain after increasing exercise fi tness pro- gramme. a Sagittal T1-weighted MR image with stress fracture evident (arrow). b Coronal T2-weighted fat sup- pressed MR image with stress fracture (arrow)
a b
culties with acute or chronic anticoagulation ther- apy can also cause such hematomas. Often the MRI appearances may be complex as there is repeated hemorrhage within soft tissues and muscle move- ment. The MRI appearances of hematoma depends on the state of the hemoglobin molecule, whether it is intra- or extracellular in nature (Kransdorf and Murphey 1997; Dooms et al. 1985; Gomori et
al. 1985; Rubin et al. 1987). In the hyper acute phase blood is isointense on T1-weighting and decreased on T2-weighting, refl ecting the earliest phase of oxy- genated hemoglobin to deoxyhemoglobin. With cell lysis, in the subacute phase (one week to three months old), the hemoglobin molecule becomes extracellular methemoglobin and is characteristically increased in signal intensity on T1- and T2-weighting. Weeks to
Fig. 8.6a–e. Fifteen-year-old male ice hockey player with pelvic pain and concern for Ewing’s sarcoma of ischium-pseudotu- mor: chronic apophyseal avulsion. a Coronal STIR sequence with increased marrow signal within posterior acetabulum ( ), inferior ischium (arrowhead), and widening of the ischial synchondrosis (white arrow). b AP Radiograph of the pelvis shows widening of the ischium ( ) and associated periosteal reaction medially (arrow) and inferiorly (arrowheads). c CT axial image shows asymmetrically widening ischial synchon- drosis (arrowheads) and periosteal reaction (arrows). d Despite pseudotumor diagnosis, family insisted on biopsy. Hematoxylin and eosin histology, original magnifi cation 2.5u, shows the central cleft ( ) within the distal apophyseal cartilage and chronic granulation tissue within bone (arrows) and depicts the zones of reaction: 1. underlying normal bone, 2. synchondrosis cartilage reactive changes, 3. superfi cial component of the hamstring tendon. e Hematoxylin and eosin histology, original magnifi cation 10×, shows reactive connective tissue with neovascularisation ( ) and surrounding infl ammatory cells (arrows) within normal cartilage tissue. (Case courtesy of Chris Loupatatzis, Klaus A. Siebenrock, and pathology from Edouard Stauffer)
a
c
e b
d
months later the methemoglobin breaks down into hemosiderin (Fig. 8.8) with decreased signal inten- sity on T1- and T2-weighting. Breakdown of blood products in the hematoma is not uniform with accel- erated peripheral breakdown refl ecting a low signal rim and centrally there is more inhomogeneous signal intensity. It may sometimes be diffi cult to dis- tinguish simple hematoma from a large hemorrhage into a malignant mass (Jelinek and Kransdorf 1995). A tumor nodule or rim of irregular tumor, or contrast enhancement within an irregular nodule may be helpful to distinguish the two (Jelinek and Kransdorf 1995). Hematomas may become sec- ondarily infected and present a more complex MRI appearance with more peripheral and surrounding soft tissue reaction.
8.10 Infection
Pyomyositis may occur in healthy sporty individu- als (Fig. 8.9); however the clinical picture prior to MRI strongly suggests infection with reddened skin, anatomy that is extremely painful and often systemic features such as fever. However patients with immu- nosuppression may present to MRI with a mass that
Fig. 8.7a,b. Nineteen-year-old soccer player presenting with a clinical mass. a Coronal T1-weighted MR image with vitamin capsules demarcates the mass. b Further coronal T1-weighted MR image shows focal muscle atrophy (arrow), within vastus lateralis chronic muscle tear
a
b
Fig. 8.8a,b. Twenty-eight-year-old male soccer player with mass. Enquiring after additional history, revealed a sports injury two years ago with “corked thigh”. a Axial T1-weighted MR image shows a focal fl uid collection with rectus femoris muscle with increased central signal intensity and a decreased signal intensity wall (arrow), consistent with hematoma formation and hemo- siderin deposition within the wall. b Corresponding axial T2-weighted MR image with fat suppressed depicts the hematoma
a b
is confusing both clinically and radiologically as the usual signs are not present. MRI features (Soler et al. 1996, 2000; Ogilvie et al. 2001; Abdelwahab et al. 2003) suggesting an abscess include a thickened peripheral rim on T1- and T2-weighting, which may be increased in signal intensity on T1-weighting and demonstrates marked contrast enhancement. Immu- nosuppressed patients commonly have an absence of marked adjacent soft tissue and subcutaneous edema. Fortunately atypical organisms may rarely cause abscess formation with a mass like appearance on MRI such as cysticercosis, Echinococcus granulo- sus in hydatid disease and Coccidioides immitius in Coccidioidomycosis (Jelinek and Kransdorf 1995).
In human immunosuffi ciency patients, Bartonella henselae, a Gram-negative bacillus, may rarely cause bacillary angiomatosis-focal infection in soft tissues, which is highly vascularized, and may erode and involve adjacent bone, mimicking a sarcoma (Biviji et al. 2002). This organism may also be involved in
‘cat scratch disease’ (Dong et al. 1995), as the carrier is usually a cat and is usually associated with single lymph node enlargement.
8.11
Normal Variants
Normal variants and their overuse may present as MRI pseudotumors. Normal bone marrow may occa- sionally cause concern for tumors; however use of T1-, and T2-weighting and STIR sequences usually excludes real pathology (Fig. 8.10). Supernumerary bones (styloid bone, accessory ossifi cation centers for scaphoid tuberosity) (Capelastegui et al. 1999), tarsal coalition, accessory soleus muscle, and exten- sor digitorum manu brevis muscle ( Capelastegui et al. 1999) are some targets. Occasionally tarsal coali-
Fig. 8.9a–d. Fifty-year-old female skier with forearm mass. Further his- tory obtained suggested mass occurred at site of minor trauma with ski poles. a Oblique coronal T1-weighted MR image with abscess wall sign: increased signal intensity on T1-weighting (arrow). b Axial T2- weighted MR image shows focal high signal intensity region, consis- tent with a fl uid collection. A vitamin capsule demarcating the clinical mass region is evident. c Axial T1-weighted fat suppressed MR image after administration of contrast agent shows contrast within thickened abscess wall and in adjacent soft tissues (arrow). Presumably there was secondary infection of a hematoma. d Hematoxylin and eosin histol- ogy shows a thickened irregular abscess wall. (Pathology courtesy of Edouard Stauffer)
a b c
d
tion and calcaneal spurs associated with peroneal tendon infl ammation and partial tear may be associ- ated with a marked synovial reaction and tenosynovi- tis, prompting a pseudotumor (Fig. 8.11). Awareness of these syndromes and review of the radiographs usually allows correct diagnosis, such as with the distal femoral avulsive cortical irregularity/peri- osteal desmoid, which is a normal variant around the medial aspect of the knee, frequently mistaken for a sarcoma. Schmorl’s nodes may rarely present as giant cystic-like lesions of the vertebral bodies in young patients (Hauger et al. 2001). Additional computer tomography may confi rm these diagnoses.
Ruptured Baker’s cysts with perifascial fl uid medial
to the medial calf muscles, may appear as a mass on MRI, however extension to the posteromedial knee joint should allow for the correct diagnosis.
8.12
Calcium Deposition Disorders
Hydroxyapatite, gout and calcium pyrophosphate dehydrate crystal deposition disorders with cal- cium deposition in tendons, ligaments and bursae may create MRI pseudotumors. Patients with a
c
Fig. 8.10a–c. Twenty-six-year-old female with sports related shoulder overuse, presents to MRI for clinical review and with STIR sequences only. a Axial STIR image shows red marrow signal intensity (arrow), in error diagnosed as a bone sarcoma of the proximal humerus. b Coronal STIR sequence again shows the falsely interpreted normal red marrow (arrow). c Coronal T-weighted MR image shows the normal red marrow signal intensity (arrow) can be diagnosed as a normal variant of marrow
a b
provisional clinical diagnosis of tumor associated with ligament calcifi cation may be referred for MRI (Anderson et al. 2003a). Focal thickening of the lateral collateral ligament associated with adjacent marked soft tissue reaction with intravenous gado- linium contrast enhancement, which on review of the radiographs correlated to soft tissue calcifi ca- tions. With its acute clinical onset and dissipation on follow-up radiographs, this entity is presumed to be due to hydroxyapatite deposition. Review of radiographs at the time of MRI reporting and aware- ness of this entity and others like it, is critical for correct MRI diagnosis of pseudotumor. It is more characteristic within the rotator cuff tendons of the shoulder.
8.13
Metabolic Disorders
Metabolic disorders may be associated with MRI pseudotumors such as amyloid deposition and hyper- parathyroidism, though are most unusual in sporting individuals. Secondary amyloidosis is the common- est of this unusual group, usually seen in association with chronic renal failure. It is due to the deposition of beta-2 microglobulins within joint capsules and tendon sheaths and may rarely be associated with pseudotumors near joints. Characteristically there is a decreased signal intensity on T2-weighting, which appears to refl ect the collagen-like nature of the amy-
Fig. 8.11a–d. Young female weekend athlete tries to increase her fi tness, with increasing ankle swelling. Outside MRI initially interpreted as synovial sarcoma for staging. a Oblique short axis T1-weighted MR image shows medial soft tissue swelling (arrow). b Corresponding T2-weighted MR image shows some evidence of tenosynovitis. c Corresponding T1-weighted fat suppressed MR image after intravenous contrast enhancement (arrow) shows active synovitis. d Review of lateral radiograph shows evidence of tarsal coalition (arrow) with reversed “c” sign
a
c
b
d
loid (Kransdorf and Murphey 1997). Primary, or now more commonly, secondary hyperparathyroid- ism may be associated with brown tumors of bone which are non-specifi c on MRI. The most common clinical setting is chronic renal failure and laboratory results are diagnostic with high serum calcium, low serum phosphorus and a high parathormone level.
Idiopathic tumoral calcinosis may present as an MRI pseudotumor with large septated regions of variable signal intensity in periarticular regions on both T1- and T2-weighting (Steinbach et al 1995), however review of the radiographs allows for this diagnosis.
8.14
Foreign Body Reactions
Foreign body reactions due to trauma or as a con- sequence of trauma such as retained surgical swabs (“cottonballoma”) (Fig. 8.12) (Kalbermatten et al.
2001) are fortunately less common, though should be considered in the appropriate clinical setting.
Close inspection for traces of intramedullary screws, subtle metallic artifacts or direct evidence of retained foreign bodies, such as glass (Fig. 8.13), should be sought.
8.15
Vascular Pseudoaneurysms
Less common MRI pseudotumors include hand pseu- doaneurysms (Anderson et al. 2003b). Of 25 cases, 10 presented clinically as soft tissue masses without other symptoms. These are usually caused by acute trauma with direct arterial injury; however they may be due to chronic repetitive trauma and the hypo- thenar hammer syndrome (Conn et al. 1970; McCue 1986). This syndrome describes signs and symptoms associated with ischemia of the hand and fi ngers sec- ondary to blunt repetitive injury of the ulnar artery and superfi cial volar arch against the hook of hamate.
Arterial wall damage may lead to pseudoaneurysm formation and or vessel thrombosis, micro emboli formation (Glichenstein et al. 1988) and com- pression of the sensory branch of the ulnar nerve ( Glichenstein et al. 1988). Usually described in men of working age with industrial occupations involving
repetitive blunt trauma to the hands (Newmeyer 1993; Little and Ferguson 1972) it has also been described in sports-related injuries in handball play- ers and baseball catchers (Glichenstein et al. 1988;
Newmeyer 1993; Little and Ferguson 1972). The thenar hammer syndrome (Janevski in Green et al.
1979) involves acute or chronic compression of the radial artery between the fi rst and second metacarpal where the artery is more superfi cial in location and covered only by the muscle of fl exor pollicis brevis and subcutaneous fat. The commonest pseudoaneu- rysms involve the popliteal artery, and if due to arte- riosclerosis they will be bilateral in up to 75% of cases (Kransdorf and Murphey 1997). Adding an MR angiography sequence may give the diagnosis here.
8.16
Post Treatment/Intervention and Others
Though rare in sporting individuals, post therapy including post radiation MRI appearances may be associated with an MRI pseudotumor. Radiotherapy MRI fi ndings of altered soft tissue and bone marrow signal intensities may be suspicious, however on close review there is usually no real mass and review of the radiotherapy details and port positioning usually allow a correct diagnosis (Richardson et al. 1996).
Usually the history is apparent.
8.17
Rheumatological or
Degenerative Joint Disease
Young sports people may also fi rst present with mono-articular joint disease or due to overuse with advanced degenerative joint disease. Laboratory screens are helpful here.
8.18
AVN and Transient Osteoporosis
Avascular necrosis may occasionally mimic a carti- lage lesion on radiographs, but the presence of the
Fig. 8.12a–e. Male patient with increasing mass after femur fracture and internal fi xation 25 years previously. a Axial T1- weighted MR image shows large surface/cortical inhomo- geneous lesion (arrow). b Corresponding axial T2 weighted image shows variable signal (arrow) within the mass. c Para- sagittal T2-weighted MR image with osteosynthesis screw holes (arrow), consistent with previous surgery. d Gross pathological specimen with retained surgical swab (arrow).
e Interference microscopy image shows calcifi c deposition within cotton swab. (Pathology and interference microscopy courtesy of Edouard Stauffer)
a
c
e b
d
classical double geographic line sign should make this diagnosis obvious on MRI. Transient osteoporo- sis of bone may rarely mimic a tumor, with altered bone marrow signal intensity initially described within the proximal femur and also knee joint region, however there is a lack of a real mass and the pain and marrow signal subside.
8.19
Muscle Denervation
Post-surgical denervation muscle fi nding at MRI may mimic a tumor, particularly in the acute phase where this swelling and edema within muscle, how- ever there is an absence of a mass. This may occur around the knee after minor sports related trauma, with common peroneal nerve injury (Fig. 8.14).
Fig. 8.14. Young male jogger presents with lower limb subtle swelling after minor trauma. Axial STIR shows subtle anterior compartment altered muscle signal intensity (arrow) consis- tent with peroneal nerve acute denervation atrophy. Further images excluded a mass around the knee joint
Fig. 8.13a–c. Eighteen-year-old jogger with swelling after minor trauma. a Coronal STIR shows subtle muscle altered signal intensity (arrow). b Axial T1-weighted MR image shows a small retained foreign body (arrow). c Corresponding axial T2-weighted MR image with fat suppressed shows the glass fragment
a
c b
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Things to Remember
1. Check for history of trauma – think myositis ossifi cans.
2. Review history for specifi c sport and repeti- tive activity – think overuse/tears of liga- ments, muscles and stress reactions or fractures.
3. Ascertain whether a true focal mass is present.
4. Always correlate MRI with radiographs and/
CT.
5. In case of superfi cial lesion – think hema- toma/fat necrosis
6. In case of intra-muscular lesion – think hematoma / infection / myositis ossifi cans (tide mark sign).
7. Remember age specifi c lesions.
8. Aging population – more osteoporosis and insuffi ciency fractures.
9. Check risk factors for AVN.
10. Adolescents – stress reactions and fractures chronic avulsion fractures may mimic neo- plastic lesion.
11. Joint lesions – remember systemic disorders may fi rst present in one joint.
12. Marked irregular synovitis – think rheuma- tological disorder or infection.
13. Abscess wall sign – increased signal on T1- weighting within thickened wall.
14. Ensure T1-weighting to review for normal marrow signal.
15. Exclude normal variants with overuse – check radiographs.
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