Imaging Evaluation of Foot and Ankle Pathology: Self-Assessment Module

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1 Imaging Evaluation of Foot and Ankle Pathology: Self-Assessment Module Catherine C. Roberts 1, William B. Morrison 2, and Patrick T. Liu 1 AJR Integrative Imaging LIFELONG LEARNING FOR RADIOLOGY ABSTRACT The educational objectives of this self-assessment module are for the participant to exercise, self-assess, and improve his or her understanding of the imaging evaluation of foot and ankle pathology. INTRODUCTION This self-assessment module on the imaging evaluation of foot and ankle pathology has an educational component and a self-assessment component. The educational component consists of three 30-minute webcasts for the participant to view. The self-assessment component consists of nine multiple-choice questions with solutions. All of these materials are available on the ARRS Web site ( To claim CME and SAM credit, each participant must enter his or her responses to the questions online. EDUCATIONAL OBJECTIVES By completing this educational activity, the participant will: A. Exercise, self-assess, and improve his or her understanding of the imaging evaluation of foot and ankle masses. B. Exercise, self-assess, and improve his or her understanding of the imaging of foot and ankle infections. C. Exercise, self-assess, and improve his or her understanding of optimizing CT of the foot and ankle. REQUIRED ACTIVITIES (available at 1. Roberts CC. MRI of foot and ankle masses. ARRS webcast. Published February 20, Accessed February 20, Morrison WB. Imaging of foot and ankle infection. ARRS webcast. Published February 20, Accessed February 20, Liu PT. MDCT of the foot and ankle: technique and applications. ARRS webcast. liu/. Published February 20, Accessed February 20, 2007 INSTRUCTIONS 1. View the required webcast materials. 2. Visit and select Publications/Journals/ SAM Articles from the left-hand menu bar. 3. Using your member login, order the online SAM as directed. 4. Follow the online instructions for entering your responses to the self-assessment questions and then complete the test by answering the questions online. Keywords: ankle, CT, foot, infection, mass, MRI DOI: /AJR Received June 19, 2007; accepted after revision September 17, Department of Radiology, Mayo Clinic College of Medicine, 5777 E Mayo Blvd., Phoenix, AZ Address correspondence to C. C. Roberts (roberts.catherine@mayo.edu). 2 Department of Radiology, Thomas Jefferson University Hospital, Philadelphia, PA. AJR 2008;190:S18 S X/08/1903 S18 American Roentgen Ray Society S18 AJR:190, March 2008

Foot and Ankle Pathology QUESTION 1 Which soft-tissue mass is MOST common in foot and ankle? A. Morton s neuroma. B. Pigmented villonodular synovitis. C. Ganglion cyst. D. Plantar fibromatosis. E.

2 Foot and Ankle Pathology QUESTION 1 Which soft-tissue mass is MOST common in foot and ankle? A. Morton s neuroma. B. Pigmented villonodular synovitis. C. Ganglion cyst. D. Plantar fibromatosis. E. Hemangioma. QUESTION 2 An MRI appearance of homogeneous low T1- and T2-weighted signal with enhancement is MOST typical of which foot and ankle mass? A. Morton s neuroma. B. Lipoma. C. Ganglion cyst. D. Plantar fibromatosis. E. Hemangioma. QUESTION 3 Which is the most specific examination for characterization of a soft-tissue neoplasm in the foot? A. MRI. B. PET. C. CT. D. Sonography. E. Radiography. QUESTION 4 With respect to the foot of a diabetic patient in Figure 1, which of the following statements is TRUE? A. Enhancement of the soft tissue around the ulcer represents devitalization. B. A rim-enhancing sinus tract extends from the ulcer to the bone, but there is clearly no osteomyelitis. C. Cystic change seen at the midfoot is compatible with osteoarthritis or neuropathic osteoarthropathy. D. There is evidence of osteomyelitis involving the fifth metatarsal bone. E. Findings are compatible with neuropathic disease with no osteomyelitis. Fig. 1 Short-axis T1-weighted fat-suppressed contrast-enhanced image of the foot of 56-year-old diabetic man with plantar ulceration. QUESTION 5 Regarding the MRI protocol for evaluation of diabetic pedal disease, which of the following statements is TRUE? A. The head coil is recommended for imaging both feet at once. B. Field of view should always be large to include the lower calf. C. No fat suppression is needed for T2-weighted imaging. D. A STIR sequence can be useful to provide more homogeneous fat suppression. E. IV gadolinium contrast material provides no benefit. QUESTION 6 Which of the following statements is TRUE? A. After amputation, marrow edema and enhancement of the marrow is considered a normal finding on MRI. B. In the setting of diabetes, soft-tissue edema on T2-weighted MR images is consistent with cellulitis. C. Diabetic pedal infection typically is due to the hematogenous spread of bacteria. D. Neuropathic disease of the feet in diabetes makes a patient more susceptible to infection. E. The most common site for neuropathic osteoarthropathy of the diabetic foot is the metatarsophalangeal region. AJR:190, March 2008 S19

3 QUESTION 7 When performing a CT examination on a patient who has a metal fixation screw placed for posterior subtalar arthrodesis, which of the following is TRUE? A. The scanning plane should be oriented perpendicular to the long axis of the screw to limit metal artifact to the fewest number of slices. B. Multiplanar reformations are made from raw CT data sets. C. The hindfoot should be scanned in both the axial and the coronal planes. D. Detector collimation should be increased to > 1 mm to maximize the signal-to-noise ratio of the images. E. If the subtalar joint has bone fusion across 50% of the length of the joint on a sagittal series, then the fusion is probably stable. QUESTION 8 Which of the following statements about fractures around the ankle is TRUE? A. Pilon fractures are usually due to external rotation injuries. B. Extension of a talar neck fracture through the talar dome articular surface is associated with a high rate of posttraumatic arthritis. C. The risk of talar dome avascular necrosis after a talar neck fracture is high if the fracture extends through the anterior process. D. Fractures of the sustentaculum tali are usually due to avulsion by the deltoid ligament. E. The blood supply to the talar dome enters at the anterior process. QUESTION 9 Concerning fracture healing, which of the following is TRUE? A. A 10-month-old fracture that has not yet healed, but shows slight progression of endosteal bridging and callus formation, can be considered a non union. B. A 6-month-old fracture that has radiolucency of the fracture line and mild callus formation cannot be considered a delayed union. C. A hypertrophic fracture nonunion will have a better chance of healing if a bone graft is used to increase mechanical stability. D. An atrophic fracture nonunion will have an increased chance of healing if an external fixator is used to improve stability. Solution to Question 1 Ganglion cyst is the most common soft-tissue mass of the foot and ankle [1]. Ganglion cysts are focal collections of mucoid material found near a joint or tendon sheath [2]. Option C is the best response. Morton s neuroma is less common than ganglion cyst. Morton s neuromas are a fibrosing degenerative process surrounding a plantar digital nerve, not a true neuroma. Option A is not the best response. Pigmented villonodular synovitis (PVNS) is less common than ganglion cysts. PVNS is a proliferative synovial disorder resulting in a single or multiple intraarticular masses. Giant cell tumor of tendon sheath is the focal form of PVNS affecting a tendon sheath or bursa. These lesions can show intense heterogeneous enhancement. The multiple synovial masses in PVNS contain regions of low T1- and T2-weighted signal, which bloom on gradient-echo sequences because of hemosiderin. Option B is not the best response. Plantar fibromatosis consists of aggregates of fibroblasts in the plantar fascia. The classic location involves the superficial medial aspect of the plantar fascia. Option D is not the best response. Hemangiomas are not the most common mass in the foot, although they are the most common tumor of vascular origin [3]. Option E is not the best response. Solution to Question 2 Masses predominantly composed of fibrous tissue can have homogeneously low T1- and T2-weighted signal with enhancement. This is most commonly seen in fibrous masses containing mature collagen. Fibrosing masses containing immature fibrous tissue or fibroblasts can have intermediate signal intensity. Fibrosing masses include plantar fibromatosis and fibroma of tendon sheath. Option D is the best response. Morton s neuromas typically have intermediate signal that is isointense to muscle on T1-weighted and low signal on T2-weighted sequences with variable enhancement [4]. Option A is not the best response. Lipomas follow fat signal intensity. They typically have high T1- and T2- weighted signal and low signal on fat-suppressed sequences [5]. Option B is not the best response. The typical appearance of a ganglion cyst on MRI is a well-defined mass with low T1- and high T2-weighted signal. Uncomplicated ganglion cysts do not have central enhancement, although a thin rim of enhancement may surround the ganglion. If a suspected ganglion cyst has central enhancement, then malignancy must be excluded. Option C is not the best response. Hemangiomas have mixed signal on T1- and T2- weighted sequences because of the presence of vessels, fat, and fibrous tissue [3]. The vascular portions of hemangiomas homogeneously enhance. Option E is not the best response. Densely calcified masses can have low T1- and T2- weighted signal, but would not be expected to enhance. Solution to Question 3 MRI is the study of choice for the evaluation of soft-tissue neoplastic masses in the foot [6]. MRI signal characteristics combined with the location of the mass can reveal a character- S20 AJR:190, March 2008

4 Foot and Ankle Pathology istic appearance for several entities. Enhancement characteristics can be important when assessing soft-tissue masses in the foot and are most helpful in differentiating benign cysts from solid masses [6]. Malignant masses in the foot can be well defined and have T1- and T2-weighted signal similar to cysts, thus making the presence or absence of enhancement critical for differentiation [7]. Unenhanced MRI is also widely used and, for some foot masses, performs as well as enhanced MRI. Option A is the best response. PET, especially when combined with CT, has great promise for staging musculoskeletal neoplasms but has not been proven to characterize masses more specifically than MRI. Option B is not the best response. CT is not the diagnostic imaging study of choice. CT can be useful for assessing the underlying bone, but does not best characterize soft-tissue masses. However, CT can confirm the presence of fat in a mass. Option C is not the best response. Sonography of soft-tissue masses is relatively nonspecific when compared with enhanced MRI. Option D is not the best response. Radiography poorly characterizes soft-tissue masses, but can assess the underlying bone. Option E is not the best response. Solution to Question 4 Subchondral cysts are a hallmark of degenerative arthritis; osteoarthritis is common at Lisfranc s (tarsometatarsal) joint. In the setting of diabetes, chronic neuropathic osteoarthropathy should also be considered. Acute inflammatory conditions such as septic arthritis do not result in cyst formation. Therefore, the presence of subchondral cysts argues against septic arthritis in patients with marrow abnormality. Osteoarthritis with superimposed infection remains a possibility, but infection rapidly destroys the cartilage and subchondral plate, resulting in the initial disappearance or obscuration of cysts [8]. After infection clears, secondary osteoarthritis results in the reappearance of cysts. Option C is the best response. Although enhancement is present in the medial plantar tissues around the ulcer, no enhancement would be seen with devitalization of the soft tissues [9, 10]. This finding represents cellulitis. Option A is not the best response. In general, in the setting of diabetic foot ulceration when there is communication of the skin surface and bone (via deep ulceration or sinus tract), osteomyelitis is often present [9, 11, 12]. Enhancement of the first cuneiform adjacent to the sinus tract disproportionate to the rest of the Lisfranc joint suggests early osteomyelitis. Option B is not the best response. The fifth metatarsal bone shows normal signal, which is low on this fat-suppressed T1-weighted image [12]. Option D is not the best response. As with option C, cysts are compatible with a neuropathic joint. However, a sinus tract extending from an ulcer to the medial cuneiform with adjacent marrow enhancement should suggest the presence of superimposed osteomyelitis [9, 11, 12]. Option E is not the best response. Solution to Question 5 Heterogeneous fat suppression can result from a variety of factors, including nearby metal or a large field of view. If presaturation of fat resonance frequency results in a heterogeneous signal, an inversion recovery sequence, which provides more homogeneous fat suppression, should be performed [9, 12]. Option D is the best response. The smallest coil available to image the desired field of view should always be used [9]. Imaging both feet with a head coil appears more efficient but results in suboptimal imaging of both sides. Each foot should be imaged separately. Option A is not the best response. The calf should be included if there is clinical concern for proximal spread of infection. However, this is relatively rare [11], and the large field of view renders interpretation of the small bones of the foot limited because they are subject to volume averaging effects. Option B is not the best response. Infection results in edema: marrow edema in osteomyelitis and soft-tissue edema in cellulitis [12]. On T2-weighted spin-echo and especially fast spin-echo imaging, fat in marrow and subcutaneous tissues is hyperintense, which can obscure subtle areas of edema [9]. Fat suppression should be used when available unless there is significant artifact [9, 10, 12]. Option C is not the best response. IV gadolinium contrast material facilitates identification of abscesses, sinus tracts, and devitalized regions; differentiation of cellulitis from diabetic soft-tissue edema; and differentiation of bland fluid from septic arthritis and septic tenosynovitis [9 12]. Option E is not the best response. Solution to Question 6 Neuropathic disease can lead to skin breaks due to minor trauma such as toenail cutting. Also, decreased perception of injury and inflammation can cause propagation of ulcers as well as superinfection [9, 11, 12]. Neuropathic disease with joint deformity and muscle imbalance can also lead to abnormal prominences that result in callus formation. Ischemic calluses subsequently break down, forming ulcers [8]. Option D is the best response. After amputation, marrow signal is generally normal, even shortly after surgery. Therefore, a diabetic patient presenting with wound breakdown after amputation who has marrow edema and enhancement at the amputation site on MRI should be considered highly suspicious for underlying osteomyelitis [9]. Option A is not the best response. Diffuse soft-tissue edema is quite common in the feet of diabetic patients on MR images [9, 10, 12]. This may be related to vascular insufficiency or neuropathy, but it does not necessarily imply the presence of inflammation. IV contrast material can distinguish diabetic edema from inflammation if there is adequate blood flow [10, 12]. Option B is not the best response. In most areas of the body, the hematogenous route is the most common mode for the spread of infection. However, in the diabetic foot, the overwhelming mode ( 90%) is contiguous spread from adjacent soft-tissue ulceration [9, 11, 12]. Option C is not the best response. The most common site for neuropathic osteoarthropathy in feet of diabetic patients is AJR:190, March 2008 S21

5 Roberts et al. Lisfranc s joint. The metatarsal bases subluxate superiorly relative to the midfoot, leading to a rocker-bottom foot deformity. The intertarsal joints, Chopart s joint, ankle, and subtalar joint also are common sites of involvement. Neuropathic osteoarthropathy occurs at the metatarsophalangeal joints but is relatively less common in this location [8]. Option E is not the best response. Solution to Question 7 Bone fusion across more than 50% of the joint space indicates that the arthrodesis is likely stable. Option E is the best response. To limit metal artifact from the screw to the fewest number of slices, the scanning plane should be aligned parallel to metal screws, not perpendicular. This will concentrate all of the artifact on a few slices, leaving the rest of the slices essentially undegraded. This can be useful when assessing an arthrodesis of a small joint, such as the subtalar joint. Orienting the gantry perpendicular to metal screws is another good positioning option. This will spread the artifact over all of the slices, instead of concentrating it in a few. Option A is not the best response. Raw CT data are the digital form of scan data, not viewable in an image format until they are reconstructed with operatorspecified field of view, kernel, slice thickness, and spacing. Multiplanar reformations (MPRs) are made from minimalthickness axial source images, not raw data [13]. Option B is not the best response. The ankle should be scanned in only one plane. Two reconstructions should be made: one set of axial 2- to 3-mm thick axial slices for routine review and a set of thin overlapping source images that will be used to make MPRs in the other desired planes. Option C is not the best response. Because the minimum slice reconstruction width is limited by the detector collimation, increasing the collimation width will result in thicker source images to be used for MPRs. The resulting MPRs will have blurring of small structures such as bone trabeculae. Option D is not the best response. Solution to Question 8 Extension of a fracture into the talar dome is likely to lead to posttraumatic degenerative joint disease, usually affecting both the ankle and the subtalar joints [14]. Option B is the best response. Pilon fractures usually are due to axial loading injuries, such as a fall from a height. Option A is not the best response. The risk of avascular necrosis of the talus is increased with subluxation or dislocation of the subtalar or ankle joint but is unrelated to involvement of the anterior process. Option C is not the best response. Fractures of the sustentaculum tali usually are due to vertical shear forces from axial loading injuries. Option D is not the best response. The blood supply to the talar dome consists of branches of the anterior tibial artery that enter the bone at the talar neck. Option E is not the best response. Solution to Question 9 A hypertrophic nonunion is thought to have hypervascularity and a capacity for biologic activity; however, healing is hindered by a lack of mechanical stability. Option C is the best response. Fracture nonunion is defined as a lack of healing 9 months after the fracture occurred and 3 months without progression of healing [15]. Option A is not the best response. Delayed union of a fracture is defined as failure to unite completely as expected, but with continued biologic activity. Option B is not the best response. An atrophic nonunion is thought to be avascular and lacks the biologic capacity to heal, even with proper stabilization. Debridement or a vascularized bone graft would be needed to stimulate healing. Option D is not the best response. References 1. Kirby EJ, Shereff MJ, Lewis MM. Soft-tissue tumors and tumor-like lesions of the foot. An analysis of eighty-three cases. J Bone Joint Surg Am 1989; 71: Weishaupt D, Schweitzer ME, Morrison WB, Haims AH, Wapner K, Kahn M. MRI of the foot and ankle: prevalence and distribution of occult and palpable ganglia. J Magn Reson Imaging 2001; 14: Woertler K. Soft tissue masses in the foot and ankle: characteristics on MR imaging. Semin Musculoskelet Radiol 2005; 9: Llauger J, Palmer J, Monill JM, Franquet T, Bagué S, Rosón N. MR imaging of benign soft-tissue masses of the foot and ankle. RadioGraphics 1998; 18: Roberts CC, Liu PT, Colby TV. Encapsulated versus nonencapsulated superficial fatty masses: a proposed MR imaging classification. AJR 2003; 180: Maldjian C, Rosenberg ZS. MR imaging features of tumors of the ankle and foot. Magn Reson Imaging Clin N Am 2001; 9: , xii 7. Sundaram M. MR imaging of soft tissue tumors: an overview. Semin Musculoskelet Radiol 1999; 3: Ahmadi ME, Morrison WB, Carrino JA, Schweitzer ME, Raikin SM, Ledermann HP. Neuropathic arthropathy of the foot with and without superimposed osteomyelitis: MR imaging characteristics. Radiology 2006; 238: Ledermann HP, Morrison WB. Differential diagnosis of pedal osteomyelitis and diabetic neuroarthropathy: MR imaging. Semin Musculoskelet Radiol 2005; 9: Ledermann HP, Schweitzer ME, Morrison WB. Nonenhancing tissue on MR imaging of pedal infection: characterization of necrotic tissue and associated limitations for diagnosis of osteomyelitis and abscess. AJR 2002; 178: Ledermann HP, Morrison WB, Schweitzer ME. MR image analysis of pedal osteomyelitis: distribution, patterns of spread, and frequency of associated ulceration and septic arthritis. Radiology 2002; 223: Morrison WB, Schweitzer ME, Batte WG, Radack DP, Russel KM. Osteomyelitis of the foot: relative importance of primary and secondary MR imaging signs. Radiology 1998; 207: Prokop M. General principles of MDCT. Eur J Radiol 2003; 45[suppl 1]:S4 S Lindvall E, Haidukewych G, DiPasquale T, Herscovici D Jr, Sanders R. Open reduction and stable fixation of isolated, displaced talar neck and body fractures. J Bone Joint Surg Am 2004; 86: Delee JC, Drez D. The biology of fracture healing. In: Delee and Drez s Orthopedic Sports Medicine, 2nd ed. Philadelphia, PA: Saunders, 2003 S22 AJR:190, March 2008

MR Imaging of Bone Marrow Changes in the Diabetic Foot

MR Imaging of Bone Marrow Changes in the Diabetic Foot Poster No.: C-1453 Congress: ECR 2011 Type: Educational Exhibit Authors: E. A. Fatone, T. R. Toledano, A. Cotten, A. Weis, J. Beltran ; 1 1 2 2 3