(Radiographics. 2001;21:1425-1440.)
© RSNA, 2001
Forefoot Pain Involving the Metatarsal Region: Differential Diagnosis with MR Imaging1
Carol J. Ashman, MD,
Rosemary J. Klecker, MD and
Joseph S. Yu, MD
1 From the Department of Radiology, Ohio State University Medical Center, S209 Rhodes Hall, Columbus, OH 43210. Presented as an education exhibit at the 2000 RSNA scientific assembly. Received March 16, 2001; revision requested April 3 and received June 19; accepted July 10. Address correspondence to C.J.A. (e-mail: cajaas@yahoo.com).
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Abstract
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Many disorders produce discomfort in the metatarsal region of the forefoot. These disorders include traumatic lesions of the soft tissues and bones (eg, turf toe, plantar plate disruption, sesamoiditis, stress fracture, stress response), Freiberg infraction, infection, arthritis, tendon disorders (eg, tendinosis, tenosynovitis, tendon rupture), nonneoplastic soft-tissue masses (eg, ganglia, bursitis, granuloma, Morton neuroma), and, less frequently, soft-tissue and bone neoplasms. Prior to the advent of magnetic resonance (MR) imaging, many of these disorders were not diagnosed noninvasively, and radiologic involvement in the evaluation of affected patients was limited. However, MR imaging has proved useful in detecting the numerous soft-tissue and early bone and joint processes that occur in this portion of the foot but are not depicted or as well characterized with other imaging modalities. Frequently, MR imaging allows a specific diagnosis based on the location, signal intensity characteristics, and morphologic features of the abnormality. Consequently, MR imaging is increasingly being used to evaluate patients with forefoot complaints. Radiologists should be familiar with the differential diagnosis and MR imaging features of disorders that can produce discomfort in this region.
Index Terms: Arthritis, 465.70 • Foot, fractures, 465.415 • Foot, infection, 465.21 • Foot, MR, 465.1214, 465.121413 • Foot, neoplasms, 465.30 Joints, diseases, 465.70 • Joints, MR, 465.1214
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LEARNING OBJECTIVES FOR TEST 3
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After reading this article and taking the test, the reader will be able to:
- Describe the MR imaging features of common bone lesions and joint processes that can produce pain in the metatarsal region of the forefoot.
- List the MR imaging features of soft-tissue disorders that produce forefoot pain proximal to the toes.
- Formulate a differential diagnosis of soft-tissue masses of the metatarsal region.
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Introduction
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Forefoot pain is a common clinical problem. Numerous disease processes produce pain in the region of the metatarsal bones, and the cause may be difficult to establish based solely on clinical findings. Although conventional radiography is useful in detecting bone lesions, it typically does not allow diagnosis of early bone abnormalities or soft-tissue disorders producing forefoot pain. Magnetic resonance (MR) imaging, with its excellent soft-tissue contrast and multiplanar imaging capability, plays an important role in the evaluation of patients with discomfort in this region of the foot. Often, a specific diagnosis is revealed only at MR imaging.
In this article, we review the MR imaging appearances of disorders that are capable of producing pain in the forefoot proximal to the phalanges. These disorders include trauma-related conditions, Freiberg infraction, infection, joint disorders, tendon disorders, nonneoplastic soft-tissue masses, soft-tissue neoplasms, and bone neoplasms.
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Trauma
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Turf Toe
Turf toe most commonly occurs in football players who play on hard, artificial surfaces and wear lightweight, flexible shoes. Hyperextension injury at the first metatarsophalangeal (MTP) joint may result in partial or complete disruption of the fibrocartilaginous plantar plate, a structure that extends from the volar aspect of the metatarsal necks to the proximal phalanges of the toes and reinforces the MTP joint capsule (Fig 1) (1,2). Plantar plate rupture manifests as discontinuity of the structure, along with increased signal intensity in the soft tissues plantar to the sesamoid bones on STIR MR images (3) and increased signal intensity on T2-weighted images (4). Concomitant injury to the articular cartilage and subchondral bone may also occur (1).
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Figure 1a. (a-c) Turf toe in a 24-year-old professional football player who sustained an acute hyperextension injury at the first MTP joint. (a) Sagittal T1-weighted MR image shows a disrupted plantar plate (arrow) between the sesamoid bone and the base of the proximal phalanx of the great toe. (b) Sagittal short-inversion-time inversion recovery (STIR) MR image demonstrates edema in the region of the plantar plate (arrow). (c) Sagittal STIR MR image obtained adjacent to b demonstrates subchondral bone marrow edema (short arrow) and surface irregularity of the first metatarsal head (long arrow). (d) Intact plantar plate in an asymptomatic 30-year-old woman. Sagittal fat-suppressed fast spin-echo proton-density-weighted MR image shows the plantar plate (long arrow) as a low-signal-intensity band dorsal to the flexor tendons (short arrow).
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Figure 1b. (a-c) Turf toe in a 24-year-old professional football player who sustained an acute hyperextension injury at the first MTP joint. (a) Sagittal T1-weighted MR image shows a disrupted plantar plate (arrow) between the sesamoid bone and the base of the proximal phalanx of the great toe. (b) Sagittal short-inversion-time inversion recovery (STIR) MR image demonstrates edema in the region of the plantar plate (arrow). (c) Sagittal STIR MR image obtained adjacent to b demonstrates subchondral bone marrow edema (short arrow) and surface irregularity of the first metatarsal head (long arrow). (d) Intact plantar plate in an asymptomatic 30-year-old woman. Sagittal fat-suppressed fast spin-echo proton-density-weighted MR image shows the plantar plate (long arrow) as a low-signal-intensity band dorsal to the flexor tendons (short arrow).
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Figure 1c. (a-c) Turf toe in a 24-year-old professional football player who sustained an acute hyperextension injury at the first MTP joint. (a) Sagittal T1-weighted MR image shows a disrupted plantar plate (arrow) between the sesamoid bone and the base of the proximal phalanx of the great toe. (b) Sagittal short-inversion-time inversion recovery (STIR) MR image demonstrates edema in the region of the plantar plate (arrow). (c) Sagittal STIR MR image obtained adjacent to b demonstrates subchondral bone marrow edema (short arrow) and surface irregularity of the first metatarsal head (long arrow). (d) Intact plantar plate in an asymptomatic 30-year-old woman. Sagittal fat-suppressed fast spin-echo proton-density-weighted MR image shows the plantar plate (long arrow) as a low-signal-intensity band dorsal to the flexor tendons (short arrow).
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Figure 1d. (a-c) Turf toe in a 24-year-old professional football player who sustained an acute hyperextension injury at the first MTP joint. (a) Sagittal T1-weighted MR image shows a disrupted plantar plate (arrow) between the sesamoid bone and the base of the proximal phalanx of the great toe. (b) Sagittal short-inversion-time inversion recovery (STIR) MR image demonstrates edema in the region of the plantar plate (arrow). (c) Sagittal STIR MR image obtained adjacent to b demonstrates subchondral bone marrow edema (short arrow) and surface irregularity of the first metatarsal head (long arrow). (d) Intact plantar plate in an asymptomatic 30-year-old woman. Sagittal fat-suppressed fast spin-echo proton-density-weighted MR image shows the plantar plate (long arrow) as a low-signal-intensity band dorsal to the flexor tendons (short arrow).
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Plantar Plate Disruption
Plantar plate disruption at the second through fifth MTP joints occurs more frequently in women. The increased weight-bearing load and hyperextension forces placed on the MTP joint by high-heeled, pointed shoes (5) are likely predis-posing factors. The second MTP joint is most commonly affected. MR imaging findings include increased signal intensity in and around the plantar plate on T2-weighted images, discontinuity of the plate, MTP joint synovitis, flexor tendon sheath synovitis, and persistent hyperextension of the proximal phalanx (Fig 2) (2).
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Figure 2a. Disrupted plantar plate at the second MTP joint in a 48-year-old woman who presented with foot pain. The patient had no history of acute trauma. (a) Coronal fat-suppressed fast spin-echo proton-density-weighted MR image shows edema in the region of the plantar plate. The lateral aspect of the plate is not visualized (arrow). (b, c) Sagittal gadolinium-enhanced fat-suppressed T1-weighted MR images obtained at the medial (b) and lateral (c) aspects of the second MTP joint show a thin, irregular, indistinct plantar plate medially (arrows in b). The plate appears to be disrupted laterally (arrow in c). Note the fluid accumulation and contrast material enhancement within the joint and the adjacent flexor tendon sheath, findings that indicate synovitis and tenosynovitis, respectively. The proximal phalanx is hyperextended.
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Figure 2b. Disrupted plantar plate at the second MTP joint in a 48-year-old woman who presented with foot pain. The patient had no history of acute trauma. (a) Coronal fat-suppressed fast spin-echo proton-density-weighted MR image shows edema in the region of the plantar plate. The lateral aspect of the plate is not visualized (arrow). (b, c) Sagittal gadolinium-enhanced fat-suppressed T1-weighted MR images obtained at the medial (b) and lateral (c) aspects of the second MTP joint show a thin, irregular, indistinct plantar plate medially (arrows in b). The plate appears to be disrupted laterally (arrow in c). Note the fluid accumulation and contrast material enhancement within the joint and the adjacent flexor tendon sheath, findings that indicate synovitis and tenosynovitis, respectively. The proximal phalanx is hyperextended.
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Figure 2c. Disrupted plantar plate at the second MTP joint in a 48-year-old woman who presented with foot pain. The patient had no history of acute trauma. (a) Coronal fat-suppressed fast spin-echo proton-density-weighted MR image shows edema in the region of the plantar plate. The lateral aspect of the plate is not visualized (arrow). (b, c) Sagittal gadolinium-enhanced fat-suppressed T1-weighted MR images obtained at the medial (b) and lateral (c) aspects of the second MTP joint show a thin, irregular, indistinct plantar plate medially (arrows in b). The plate appears to be disrupted laterally (arrow in c). Note the fluid accumulation and contrast material enhancement within the joint and the adjacent flexor tendon sheath, findings that indicate synovitis and tenosynovitis, respectively. The proximal phalanx is hyperextended.
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Sesamoiditis
Sesamoiditis is a painful inflammatory condition produced by repetitive injury to the plantar aspect of the forefoot (6). MR imaging findings in the marrow of the sesamoid bones include decreased or normal signal intensity on T1-weighted images and increased signal intensity on STIR images (Fig 3). The bone signal intensity changes are similar to those caused by a stress response, and there may be some overlap between these conditions. If the signal intensity of the sesamoid bones is abnormal on STIR MR images but normal on T1-weighted images, sesamoiditis is a more probable diagnosis than a stress response. Involvement of both sesamoid bones also favors a diagnosis of sesamoiditis. Reactive soft-tissue abnormalities including tendinitis, synovitis, and bursitis are characteristic findings in sesamoiditis and are useful differentiating features (3).
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Figure 3a. Sesamoiditis in a 21-year-old female kickboxer. (a) Coronal T1-weighted MR image shows the tibial and fibular sesamoid bones with low signal intensity (arrows). (b) Corresponding coronal STIR MR image shows the sesamoid bones with increased signal intensity (long arrows). Note the adjacent soft-tissue edema and joint effusion. Involvement of both sesamoid bones, joint effusion, and inflammatory changes in the adjacent soft tissues favor a diagnosis of sesamoiditis rather than stress response. However, the small amount of bone marrow edema within the first metatarsal head (short arrow) probably represents a stress response.
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Figure 3b. Sesamoiditis in a 21-year-old female kickboxer. (a) Coronal T1-weighted MR image shows the tibial and fibular sesamoid bones with low signal intensity (arrows). (b) Corresponding coronal STIR MR image shows the sesamoid bones with increased signal intensity (long arrows). Note the adjacent soft-tissue edema and joint effusion. Involvement of both sesamoid bones, joint effusion, and inflammatory changes in the adjacent soft tissues favor a diagnosis of sesamoiditis rather than stress response. However, the small amount of bone marrow edema within the first metatarsal head (short arrow) probably represents a stress response.
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Stress Fractures
Stress fractures in the metatarsal bones are common in runners, ballet dancers, gymnasts, and military recruits (7). Conditions resulting in altered weight bearing , including a hallux valgus deformity, recent surgery of the hallux, and a low longitudinal arch of the foot, increase the risk of developing a stress fracture. The middle or distal portions of the second, third, or fourth metatarsal shafts are most often involved. Stress injuries may also occur in the sesamoid bones of the hallux and at the synchondrosis between the portions of a bipartite sesamoid bone (6). Subchondral fractures may occur in the metatarsal head in diabetic patients with neuropathic arthropathy; these fractures may appear identical to a stress fracture (8).
Stress Response
A stress response manifests as an amorphous area of decreased signal intensity within the marrow on T1-weighted MR images that increases in signal intensity on corresponding T2-weighted and STIR images. Edema may be present in the adjacent soft tissues, and contrast enhancement may occur following intravenous administration of gadopentetate dimeglumine. These findings are nonspecific, and correlation with clinical findings is essential for making a correct diagnosis. A stress response may progress to a stress fracture, which is characterized by a band of low signal intensity contiguous with the cortex on both T1- and T2-weighted images (Fig 4) (9–11).
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Figure 4a. Stress fracture of the second metatarsal shaft in a 19-year-old male runner. The patient had no history of acute trauma. (a) Axial T1-weighted MR image shows cortical thickening, a low-signal-intensity horizontal band representing a fracture line spanning the width of the bone (arrows), and adjacent low-signal-intensity changes within the marrow. (b) Coronal T2-weighted MR image shows increased signal intensity within the marrow and adjacent soft tissues (arrows). (c) On a gadolinium-enhanced fat-suppressed T1-weighted MR image, the fracture line is more conspicuous (arrows). Note the intense contrast enhancement of the adjacent bone marrow and soft tissues.
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Figure 4b. Stress fracture of the second metatarsal shaft in a 19-year-old male runner. The patient had no history of acute trauma. (a) Axial T1-weighted MR image shows cortical thickening, a low-signal-intensity horizontal band representing a fracture line spanning the width of the bone (arrows), and adjacent low-signal-intensity changes within the marrow. (b) Coronal T2-weighted MR image shows increased signal intensity within the marrow and adjacent soft tissues (arrows). (c) On a gadolinium-enhanced fat-suppressed T1-weighted MR image, the fracture line is more conspicuous (arrows). Note the intense contrast enhancement of the adjacent bone marrow and soft tissues.
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Figure 4c. Stress fracture of the second metatarsal shaft in a 19-year-old male runner. The patient had no history of acute trauma. (a) Axial T1-weighted MR image shows cortical thickening, a low-signal-intensity horizontal band representing a fracture line spanning the width of the bone (arrows), and adjacent low-signal-intensity changes within the marrow. (b) Coronal T2-weighted MR image shows increased signal intensity within the marrow and adjacent soft tissues (arrows). (c) On a gadolinium-enhanced fat-suppressed T1-weighted MR image, the fracture line is more conspicuous (arrows). Note the intense contrast enhancement of the adjacent bone marrow and soft tissues.
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Radiographically Occult Fractures
Radiographically occult fractures can be accurately detected with MR imaging. The fracture line appears as a linear abnormality with low signal intensity on T1-weighted images. Marrow with low signal intensity on T1-weighted images and high signal intensity on corresponding T2-weighted and STIR images surrounds the fracture (4). MR imaging is particularly useful in detecting occult fractures in osteopenic patients.
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Freiberg Infraction
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Freiberg infraction is a disorder affecting the metatarsal head (usually the second or third metatarsal head) and is characterized at pathologic analysis by collapse of the subchondral bone, osteonecrosis, and cartilaginous fissures. The cause of Freiberg infraction is controversial and is probably multifactorial. A traumatic insult in the form of either acute or repetitive injury and vascular compromise are the most popular theories. Freiberg infraction is more common in women and most commonly manifests during adolescence. High-heeled shoes have been implicated as a causative factor (12). Patients may present with pain and limited motion, although symptoms may not begin until degenerative arthrosis has developed.
Early MR imaging findings include low-signal-intensity changes in the metatarsal head on T1-weighted images with increased signal intensity on corresponding T2-weighted and STIR images (4). These changes are nonspecific and may also be seen in a stress response of the metatarsal head. There may in fact be overlap between these conditions (8). With disease progression, flattening of the metatarsal head occurs, and low-signal-intensity changes develop on T2-weighted images as the bone becomes sclerotic.
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Infection
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Osteomyelitis
Osteomyelitis of the foot most often results from transcutaneous spread of infection and most commonly occurs in diabetic patients (13). Cutaneous ulcers may develop at pressure points, especially under the first and fifth metatarsal heads (14). When ulcerations become infected, contiguous spread to the underlying metatarsal head and MTP joint may occur.
MR imaging findings in osteomyelitis include low signal intensity within the infected bone marrow on T1-weighted images, increased signal intensity on T2-weighted and STIR images, and contrast enhancement following intravenous administration of gadopentetate dimeglumine (Fig 5) (13,15). Secondary signs of osteomyelitis may help distinguish between osteomyelitis and acute neuropathic disease, which demonstrates similar imaging findings (13). These secondary signs include a cutaneous ulcer, cellulitis, phlegmon, soft-tissue abscess (Fig 6), sinus tract, and cortical interruption.
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Figure 5a. Osteomyelitis of the first metatarsal head and septic arthritis of the first MTP joint in a 30-year-old woman with systemic lupus erythematosus. (a) Axial T1-weighted MR image shows an area of diffuse low signal intensity within the marrow of the distal first metatarsal bone (arrows). Similar changes were also present within the base of the proximal phalanx of the great toe. (b) Coronal T2-weighted MR image demonstrates a dorsal cutaneous ulcer (arrowheads), dorsal sinus tract (short arrows), high-signal-intensity changes in the soft tissues representing cellulitis, increased signal intensity within the marrow of the metatarsal head (*), and joint effusion (long arrow). (c) Sagittal fat-suppressed T1-weighted MR image reveals intense contrast enhancement of the bone marrow, joint, and soft tissues. Note that the extensor tendon sheath dorsal to the first ray demonstrates both edema and enhancement (arrows), findings that indicate tenosynovitis.
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Figure 5b. Osteomyelitis of the first metatarsal head and septic arthritis of the first MTP joint in a 30-year-old woman with systemic lupus erythematosus. (a) Axial T1-weighted MR image shows an area of diffuse low signal intensity within the marrow of the distal first metatarsal bone (arrows). Similar changes were also present within the base of the proximal phalanx of the great toe. (b) Coronal T2-weighted MR image demonstrates a dorsal cutaneous ulcer (arrowheads), dorsal sinus tract (short arrows), high-signal-intensity changes in the soft tissues representing cellulitis, increased signal intensity within the marrow of the metatarsal head (*), and joint effusion (long arrow). (c) Sagittal fat-suppressed T1-weighted MR image reveals intense contrast enhancement of the bone marrow, joint, and soft tissues. Note that the extensor tendon sheath dorsal to the first ray demonstrates both edema and enhancement (arrows), findings that indicate tenosynovitis.
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Figure 5c. Osteomyelitis of the first metatarsal head and septic arthritis of the first MTP joint in a 30-year-old woman with systemic lupus erythematosus. (a) Axial T1-weighted MR image shows an area of diffuse low signal intensity within the marrow of the distal first metatarsal bone (arrows). Similar changes were also present within the base of the proximal phalanx of the great toe. (b) Coronal T2-weighted MR image demonstrates a dorsal cutaneous ulcer (arrowheads), dorsal sinus tract (short arrows), high-signal-intensity changes in the soft tissues representing cellulitis, increased signal intensity within the marrow of the metatarsal head (*), and joint effusion (long arrow). (c) Sagittal fat-suppressed T1-weighted MR image reveals intense contrast enhancement of the bone marrow, joint, and soft tissues. Note that the extensor tendon sheath dorsal to the first ray demonstrates both edema and enhancement (arrows), findings that indicate tenosynovitis.
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Figure 6. Osteomyelitis in a 25-year-old diabetic man with burning foot pain. Sagittal gadolinium-enhanced fat-suppressed T1-weighted MR image demonstrates a low-signal-intensity fluid collection with peripheral enhancement representing an abscess plantar to the fifth metatarsal head (arrows). Note also the intense enhancement of the adjacent fifth metatarsal bone (*), a finding that indicates osteomyelitis.
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Septic Arthritis
Septic arthritis of the MTP joints is also most commonly seen in diabetic patients and is caused by the spread of infection from an adjacent soft-tissue or bone source (Fig 5) (16). MR imaging findings include increased joint fluid and synovial thickening and enhancement (4,16,17). Marrow signal intensity changes and enhancement in the subarticular bone are similar to those seen in osteomyelitis. These findings are nonspecific and may also be seen in acute neuropathic disease and inflammatory arthritis. Soft-tissue signs of infection support the diagnosis of septic arthritis.
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Joint Disorders
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Neuropathic Osteoarthropathy
Neuropathic osteoarthropathy is a common complication of diabetes mellitus (14,18). The intertarsal and tarsometatarsal joints are most commonly involved, followed by the MTP joints. Impaired pain sensation and proprioception lead to repetitive trauma and joint destabilization. Arteriovenous shunting and sympathetic nerve dysfunction produce increased blood flow and osteolysis. Joint misalignment, disorganization, and destruction and bone fragmentation are characteristic pathologic features. Although patients have impaired sensation, the disease may be painful in its acute stage.
Early MR imaging features include decreased signal intensity in the juxta-articular bone on T1-weighted images and increased signal intensity on T2-weighted and STIR images (Fig 7). Contrast enhancement may occur after intravenous administration of gadopentetate dimeglumine. The adjacent soft tissues are edematous. Acutely, these findings are nonspecific and similar to those produced by osteomyelitis, which may coexist with neuropathic disease (14,18). Skin ulcers, sinus tracts, and abscess formation adjacent to areas of abnormal bone signal intensity support the diagnosis of osteomyelitis. In difficult cases, biopsy may be the only means of excluding infection. Chronic changes in neuropathic osteoarthropathy include periarticular cyst formation, bone fragmentation, joint misalignment, joint effusion, and soft-tissue edema (15,18). Osteosclerosis demonstrates subchondral low signal intensity on T1- and T2-weighted MR images. The signal intensity of juxta-articular bone is variable on T2-weighted images, however, and high-signal-intensity changes may be present (19,20).
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Figure 7a. Early neuropathic osteoarthropathy in a 49-year-old diabetic man who complained of foot pain and swelling. The patient had no history of trauma or unusual activity. (a) Axial T1-weighted MR image shows a serpentine band of low signal intensity in the lateral cuneiform bone representing a subchondral fracture (short arrows). Adjacent low-signal-intensity bone marrow edema is also present within the proximal third metatarsal bone (long arrows). (b) Axial gadolinium-enhanced fat-suppressed T1-weighted MR image shows contrast enhancement of periarticular bone (arrows) and adjacent soft tissues.
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Figure 7b. Early neuropathic osteoarthropathy in a 49-year-old diabetic man who complained of foot pain and swelling. The patient had no history of trauma or unusual activity. (a) Axial T1-weighted MR image shows a serpentine band of low signal intensity in the lateral cuneiform bone representing a subchondral fracture (short arrows). Adjacent low-signal-intensity bone marrow edema is also present within the proximal third metatarsal bone (long arrows). (b) Axial gadolinium-enhanced fat-suppressed T1-weighted MR image shows contrast enhancement of periarticular bone (arrows) and adjacent soft tissues.
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Osteoarthritis
Osteoarthritis is a common finding in the first MTP joint and is most often produced by repetitive loading injury (21). Resultant painful limitation of motion is referred to as hallux rigidus (22). Osteoarthritis of the hallucal sesamoid articulations is also common. A hallux valgus deformity may precipitate degenerative changes in the first ray.
Joint space narrowing, marginal osteophytes, subchondral cyst formation, ossicle formation, subchondral marrow edema (which demonstrates low signal intensity on T1-weighted images and increased signal intensity on T2-weighted and STIR images), and subchondral sclerosis (with decreased signal intensity on both T1- and T2-weighted images) are characteristic MR imaging findings in osteoarthritis (Fig 8) (23).
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Figure 8. Osteoarthritis at the first MTP joint in a 50-year-old man. Axial T1-weighted MR image shows a large marginal osteophyte (long arrow), ossicles at the lateral joint margin (short arrows), medial joint space narrowing, and subchondral low signal intensity within the first metatarsal head and proximal phalanx of the great toe.
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Gout
Gout is caused by the deposition of sodium urate crystals in joints, bones, tendons, bursae, and periarticular tissue. It most commonly affects the first MTP joint, and monoarticular involvement is typical. The MR imaging features of acute gout are nonspecific and include joint effusion and synovial thickening (17). Tophaceous gout represents the chronic form of the disease. Tophi may produce bone erosions and occur at intraarticular or periarticular locations or at a distance from a joint, manifesting as a soft-tissue mass. Tophi have intermediate to low signal intensity on T1-weighted MR images. Their signal intensity is variable on T2-weighted images, but heterogeneous low signal intensity should prompt consideration of this entity (Fig 9). Contrast enhancement often occurs after administration of gadopentetate dimeglumine, particularly in acutely symptomatic patients (24). Tophaceous gout may be confused with rheumatoid arthritis, septic arthritis, or even a neoplastic process at MR imaging; correlation with the clinical presentation and serum urate level is necessary in these situations.
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Figure 9a. Tophaceous gout involving the intermetatarsal and tarsometatarsal region of the foot in a 56-year-old man with hyperuricemia who presented with foot pain and swelling. (a) Axial T1-weighted MR image shows low-signal-intensity tophi (long arrows) and adjacent periarticular erosions with characteristic overhanging edges (short arrows). The joint spaces are preserved, as is typical in gout. (b, c) Coronal proton-density-weighted (b) and T2-weighted (c) MR images obtained at the level of the tarsometatarsal joint reveal erosions (short arrows) and low-signal-intensity tophi (long arrows). (Fig 9b and 9c reprinted, with permission, from reference 24.) (d) Gadolinium-enhanced fat-suppressed T1-weighted MR image shows increased contrast enhancement of the tophi (arrows) and juxta-articular bone.
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Figure 9b. Tophaceous gout involving the intermetatarsal and tarsometatarsal region of the foot in a 56-year-old man with hyperuricemia who presented with foot pain and swelling. (a) Axial T1-weighted MR image shows low-signal-intensity tophi (long arrows) and adjacent periarticular erosions with characteristic overhanging edges (short arrows). The joint spaces are preserved, as is typical in gout. (b, c) Coronal proton-density-weighted (b) and T2-weighted (c) MR images obtained at the level of the tarsometatarsal joint reveal erosions (short arrows) and low-signal-intensity tophi (long arrows). (Fig 9b and 9c reprinted, with permission, from reference 24.) (d) Gadolinium-enhanced fat-suppressed T1-weighted MR image shows increased contrast enhancement of the tophi (arrows) and juxta-articular bone.
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Figure 9c. Tophaceous gout involving the intermetatarsal and tarsometatarsal region of the foot in a 56-year-old man with hyperuricemia who presented with foot pain and swelling. (a) Axial T1-weighted MR image shows low-signal-intensity tophi (long arrows) and adjacent periarticular erosions with characteristic overhanging edges (short arrows). The joint spaces are preserved, as is typical in gout. (b, c) Coronal proton-density-weighted (b) and T2-weighted (c) MR images obtained at the level of the tarsometatarsal joint reveal erosions (short arrows) and low-signal-intensity tophi (long arrows). (Fig 9b and 9c reprinted, with permission, from reference 24.) (d) Gadolinium-enhanced fat-suppressed T1-weighted MR image shows increased contrast enhancement of the tophi (arrows) and juxta-articular bone.
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Figure 9d. Tophaceous gout involving the intermetatarsal and tarsometatarsal region of the foot in a 56-year-old man with hyperuricemia who presented with foot pain and swelling. (a) Axial T1-weighted MR image shows low-signal-intensity tophi (long arrows) and adjacent periarticular erosions with characteristic overhanging edges (short arrows). The joint spaces are preserved, as is typical in gout. (b, c) Coronal proton-density-weighted (b) and T2-weighted (c) MR images obtained at the level of the tarsometatarsal joint reveal erosions (short arrows) and low-signal-intensity tophi (long arrows). (Fig 9b and 9c reprinted, with permission, from reference 24.) (d) Gadolinium-enhanced fat-suppressed T1-weighted MR image shows increased contrast enhancement of the tophi (arrows) and juxta-articular bone.
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Rheumatoid Arthritis
Rheumatoid arthritis commonly affects the feet. The earliest changes occur at the MTP joints (25). Pannus is inflammatory synovial tissue and demonstrates low to intermediate signal intensity on T1-weighted MR images (Fig 10). Signal intensity may vary on T2-weighted images. High signal intensity indicates hypervascular pannus. With disease chronicity, fibrous pannus develops and hemosiderin deposition may occur, demonstrating low signal intensity on T2-weighted images. Additional findings include marginal erosions adjacent to the pannus, cartilage thinning, subchondral cysts and marrow edema, joint effusion, tenosynovitis, and bursitis. Enhancement of pannus can be seen immediately after contrast material administration (26–28).
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Figure 10a. Rheumatoid arthritis in a 71-year-old woman with pain at the first MTP joint. (a) Axial T1-weighted MR image shows marginal erosions at the first metatarsal head (short arrows), low-signal-intensity synovial thickening (long arrows), and joint space narrowing. Note also the erosive changes at the interphalangeal joint of the great toe. (b) Coronal gadolinium-enhanced fat-suppressed T1-weighted MR image shows contrast enhancement of the synovium (long arrow) and subchondral bone (short arrow). The signal intensity changes in both a and b are nonspecific; however, a previously established diagnosis of rheumatoid arthritis in the hands, a lack of clinical indicators of infection, a normal serum urate level, and a positive response to steroids supported the diagnosis of rheumatoid arthritis at the first MTP and interphalangeal joints.
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Figure 10b. Rheumatoid arthritis in a 71-year-old woman with pain at the first MTP joint. (a) Axial T1-weighted MR image shows marginal erosions at the first metatarsal head (short arrows), low-signal-intensity synovial thickening (long arrows), and joint space narrowing. Note also the erosive changes at the interphalangeal joint of the great toe. (b) Coronal gadolinium-enhanced fat-suppressed T1-weighted MR image shows contrast enhancement of the synovium (long arrow) and subchondral bone (short arrow). The signal intensity changes in both a and b are nonspecific; however, a previously established diagnosis of rheumatoid arthritis in the hands, a lack of clinical indicators of infection, a normal serum urate level, and a positive response to steroids supported the diagnosis of rheumatoid arthritis at the first MTP and interphalangeal joints.
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Tendon Disorders
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Tendinosis
Tendinosis is characterized by angiofibroblastic hyperplasia, degeneration, and necrosis of the involved tendon with few or no inflammatory cells (29). On T1- and proton-density–weighted MR images, there is an area of increased signal intensity and either fusiform or diffuse tendon thickening. The areas of increased signal intensity persist on T2-weighted images if significant degeneration is present (30).
Tenosynovitis
Tenosynovitis is inflammation of the tendon sheath and may be due to synovial inflammatory disease, infection (Fig 5), or mechanical irritation.Fluid accumulates in the sheath, and contrast enhancement of the sheath typically occurs following intravenous administration of gadopentetate dimeglumine. Tenosynovitis may affect the flexor hallucis longus tendon between the sesamoid bones, where it is subject to repetitive impact, and under the base of the first metatarsal bone, where the flexor digitorum longus crosses under the flexor hallucis longus (31,32). Stenosing tenosynovitis is caused by chronic inflammation, leading to fibrosis and tendon entrapment. Tendon degeneration and rupture may also result. Reported MR imaging findings in stenosing tenosynovitis include thickening of the tendon or tendon sheath, increased fluid within the tendon sheath, and enhancement of the tendon sheath following intravenous administration of gadopentetate dimeglumine (33–35).
Tendon Ruptures
Tendon ruptures occur in tendons weakened by degeneration, repetitive microtrauma, infection, or systemic disease such as diabetes. Rupture of a normal tendon is caused by laceration or sudden force, creating discontinuity of the tendon fibers and intervening edema on T2-weighted MR images (Fig 11) (36). Partial ruptures demonstrate increased signal intensity within the tendon substance on T1-, proton-density–, and, occasionally, T2-weighted images (Fig 12) (30).
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Figure 11a. Tendon rupture due to laceration of the dorsum of the foot in a 25-year-old woman with inability to dorsiflex the great toe. (a) Sagittal fat-suppressed fast spin-echo proton-density-weighted MR image shows complete rupture of the extensor hallucis longus tendon (arrow). (b) Coronal T2-weighted MR image shows a fluid-filled gap at the expected location of the tendon at the level of the proximal first metatarsal bone (arrows).
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Figure 11b. Tendon rupture due to laceration of the dorsum of the foot in a 25-year-old woman with inability to dorsiflex the great toe. (a) Sagittal fat-suppressed fast spin-echo proton-density-weighted MR image shows complete rupture of the extensor hallucis longus tendon (arrow). (b) Coronal T2-weighted MR image shows a fluid-filled gap at the expected location of the tendon at the level of the proximal first metatarsal bone (arrows).
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Figure 12. Partial tendon rupture in a 45-year-old male softball player. Coronal proton-density-weighted MR image reveals a partial longitudinal tear in the flexor hallucis longus tendon (arrows).
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Nonneoplastic Soft-Tissue Masses
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The vast majority of soft-tissue masses of the foot are nonneoplastic. Inflammatory lesions such as bursitis and foreign body granulomas are usually painful. Noninflammatory masses may cause pain as a result of mass effect or compression of adjacent structures (37,38).
Ganglia
Ganglia are the most common soft-tissue masses of the foot and ankle. In the forefoot, a ganglion is typically located dorsal to the MTP joints and tendons. Ganglia are thought to be a result of repetitive trauma leading to mucoid cystic degeneration (39). A ganglion manifests as a well-defined mass with low to intermediate signal intensity on T1-weighted MR images depending on its protein content. Homogeneous high signal intensity is characteristic on T2-weighted and STIR images (Fig 13). Thin, peripheral rim enhancement may occur following intravenous administration of gadopentetate dimeglumine (40).
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Figure 13a. Dorsal ganglion in a 25-year-old woman who presented with a painful soft-tissue mass. (a, b) Sagittal (a) and coronal (b) T2-weighted MR images reveal a well-defined mass with high signal intensity and a mildly lobulated contour (short arrow) adjacent to the fourth extensor tendon (long arrows in a). (c) On a coronal gadolinium-enhanced fat-suppressed T1-weighted MR image, the mass demonstrates low signal intensity with peripheral enhancement (arrows).
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Figure 13b. Dorsal ganglion in a 25-year-old woman who presented with a painful soft-tissue mass. (a, b) Sagittal (a) and coronal (b) T2-weighted MR images reveal a well-defined mass with high signal intensity and a mildly lobulated contour (short arrow) adjacent to the fourth extensor tendon (long arrows in a). (c) On a coronal gadolinium-enhanced fat-suppressed T1-weighted MR image, the mass demonstrates low signal intensity with peripheral enhancement (arrows).
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Figure 13c. Dorsal ganglion in a 25-year-old woman who presented with a painful soft-tissue mass. (a, b) Sagittal (a) and coronal (b) T2-weighted MR images reveal a well-defined mass with high signal intensity and a mildly lobulated contour (short arrow) adjacent to the fourth extensor tendon (long arrows in a). (c) On a coronal gadolinium-enhanced fat-suppressed T1-weighted MR image, the mass demonstrates low signal intensity with peripheral enhancement (arrows).
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Bursitis
Bursitis can occur in the forefoot and may involve the intermetatarsal bursae or the adventitial bursae beneath the metatarsal heads (41,42). Trauma, infection, rheumatoid arthritis, and gout may all cause bursitis. The most important distinguishing feature of a bursa is its location. A well-defined fluid collection is seen at a pressure point and demonstrates low signal intensity on T1-weighted MR images and high signal intensity on T2-weighted and STIR images (Fig 14). Peripheral enhancement is seen following intravenous administration of gadopentetate dimeglumine. Small fluid collections with a transverse diameter of 3 mm or less in the first three intermetatarsal bursae may be physiologic (43).
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Figure 14a. Submetatarsal bursitis in a 60-year-old woman with pain under the second metatarsal head. (a) Coronal T2-weighted MR image shows a well-defined mass with high signal intensity (arrows). (b) On a coronal gadolinium-enhanced fat-suppressed T1-weighted MR image, the mass demonstrates low signal intensity with peripheral enhancement (arrows).
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Figure 14b. Submetatarsal bursitis in a 60-year-old woman with pain under the second metatarsal head. (a) Coronal T2-weighted MR image shows a well-defined mass with high signal intensity (arrows). (b) On a coronal gadolinium-enhanced fat-suppressed T1-weighted MR image, the mass demonstrates low signal intensity with peripheral enhancement (arrows).
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Foreign Body Granulomas
Foreign body granulomas form in response to foreign objects such as thorns or pieces of wood, glass, or plastic that have penetrated the soft tissues of the foot (44). The lesion is a nonspecific mass with low signal intensity on T1-weighted MR images (Fig 15) and high signal intensity on T2-weighted images. The signal intensity pattern may be heterogeneous, and areas of low signal intensity corresponding to fibrosis may be present on T2-weighted images (45,46). In addition, peripheral contrast enhancement has been reported (47), and surrounding inflammation may be present (44). The foreign body can sometimes be visualized, demonstrating low signal intensity with all pulse sequences.
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Figure 15a. Foreign body granuloma in a 26-year-old man. (a) Coronal proton-density-weighted MR image reveals a low-signal-intensity nodular lesion in the subcutaneous fat at the plantar aspect of the ball of the foot (long arrows). A channel communicating with the skin surface is also seen (short arrows). (b) On a coronal T2-weighted MR image, the lesion demonstrates low signal intensity (arrows). (c) Coronal gadolinium-enhanced fat-suppressed T1-weighted MR image shows the mass with peripheral enhancement (arrows), a finding that indicates inflammation.
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Figure 15b. Foreign body granuloma in a 26-year-old man. (a) Coronal proton-density-weighted MR image reveals a low-signal-intensity nodular lesion in the subcutaneous fat at the plantar aspect of the ball of the foot (long arrows). A channel communicating with the skin surface is also seen (short arrows). (b) On a coronal T2-weighted MR image, the lesion demonstrates low signal intensity (arrows). (c) Coronal gadolinium-enhanced fat-suppressed T1-weighted MR image shows the mass with peripheral enhancement (arrows), a finding that indicates inflammation.
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Figure 15c. Foreign body granuloma in a 26-year-old man. (a) Coronal proton-density-weighted MR image reveals a low-signal-intensity nodular lesion in the subcutaneous fat at the plantar aspect of the ball of the foot (long arrows). A channel communicating with the skin surface is also seen (short arrows). (b) On a coronal T2-weighted MR image, the lesion demonstrates low signal intensity (arrows). (c) Coronal gadolinium-enhanced fat-suppressed T1-weighted MR image shows the mass with peripheral enhancement (arrows), a finding that indicates inflammation.
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Calluses
Calluses may form in the subcutaneous fat adjacent to skin calluses, usually under the metatarsal heads. An area of low signal intensity on both T1- and T2-weighted MR images that enhances following intravenous administration of gadopentetate dimeglumine has been described (48).
Morton Neuromas
Morton neuromas are not true neoplasms; rather, they are masses composed of interdigital perineural fibrosis and nerve degeneration. Morton neuroma occurs between the metatarsal heads, most commonly between the third and fourth rays. The lesion is thought to arise as a result of compression of the interdigital nerve against the intermetatarsal ligament, although ischemia and compression of the nerve by an enlarged intermetatarsal bursa have also been suggested (49). Morton neuroma is more common in women, and high-heeled shoes have been implicated as a causative factor. Pain at the metatarsal head, often radiating to the toes, is characteristic (50). Morton neuroma is isointense to slightly hyperintense relative to muscle on T1-weighted MR images (Fig 16). It is iso- or hypointense relative to fat on T2-weighted images, resulting in poor lesion conspicuity. The use of gadopentetate dimeglumine is helpful because intense enhancement typically occurs on fat-suppressed T1-weighted images, increasing the conspicuity of the lesion (50,51).
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Abstract
LEARNING OBJECTIVES FOR TEST...
