1: : MRI of the whole foot, sagittal (a) T2W FS, (b &c) T1W FSE pre- and (d) ..... Table-1: Helpful MRI features to differentiate osteomyelitis from Charcot's.
Diabetic foot: spectrum of MR imaging findings. Poster No.:
C-1255
Congress:
ECR 2016
Type:
Educational Exhibit
Authors:
M. R. Nouh , M. Zidan , A. F. EID ; Alexandria/EG, El-Ahsa/SA
Keywords:
Infection, Abscess, Complications, Abscess delineation, MR, Musculoskeletal soft tissue, Musculoskeletal bone, Extremities
DOI:
10.1594/ecr2016/C-1255
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Learning objectives To highlight and review the broad spectrum of soft-tissue and osteo-articular changes seen on MR of the diabetic foot. Images for this section:
Fig. 1: : MRI of the whole foot, sagittal (a) T2W FS, (b &c) T1W FSE pre- and (d) post- contrast images; show a big heal ulcer (long open white arrow on a,b & d) with calcaneal bone marrow edema (a). No significant enhancement of the marrow was seen on post-contrast image (d) ruling out osteomyelitis. There is retraction of the frayed Achillis tendon ( thin white arrow on a, b & d) with bulbous high-signal distal end consistent with degenerative attritic tendinopathy. Note the callus (short open arrow on c) developed
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under the head of M5 due to gait imbalance and diabetic myopathy (black dotted oval on a &b). © Radiodiagnosis, Alexandria University, Faculty of Medicine - Alexandria/EG
Fig. 2: MRI of the hindfoot/Ankle region, sequential sagittal (a) pre-contrast T1W FSE, (b) T2W FS and short-axis/coronal (c) T2W FS, (d) post-contrast T1W FS images, show a big heel ulcer (open white arrows on a & c) with tumefactive oedematous soft-tissue replacement of the underlying heel fat pad and remarkable bone marrow oedema of the calcaneous (Black dotted circle in b). There is FHL tenosynovitis under the sustanaculum tali (black arrow in c). Note the enhancing tram-track like sinus tract (short black arrow on d) and multiple linear and rounded signal void air loculi (white stars on d) leaking from the open sinus. © Radiodiagnosis, Alexandria University, Faculty of Medicine - Alexandria/EG
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Background Diabetes mellitus (DM) is a worldwide growing health morbidity and mortality challenge. Diabetic affection of the foot results in neuropathic arthropathy and/or osteomyelitis. Actually, both conditions may coexist resulting in clinical diagnostic challenges. So; the radiologist role is imperative in discretion of these two entities with different management planes for the sake of limb- and life-saving results.
MR of the diabetic foot- procedural considerations:
MR imaging examination of the foot has to be individually tailored to answer the aroused clinical question. For high-yielding diagnostic MR images, it is better to image different foot sub-regions viz. forefoot, midfoot and hindfoot examinations including the ankle joint; separately (1). Sometimes, scanning of the whole foot may be done to evaluate the whole extent of the pathologic process of concern. The combination of non-contrast T1W, fat-suppressed PD and/or T2W as well as postcontrast T1W images is empirical for comprehensive MR evaluation of the foot. Watersensitive images e.g. fat-suppressed PD and/or T2W (or STIR as an alternative) are superior in perceiving marrow and soft-tissue edema. T1W images are invaluable in detection of osteomyelitis. Gadolinium-based contrast helps to delineate the extent of fluid collections and necrotic tissues warranting adequate debridement for successful management. Images for this section:
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Fig. 3: MRI of the fore-foot; short-axis (a) T2 FS, sagittal (b) non-contrast as well as (c) post-contrast T1W FSE, and short-axis (d) T1W FS as well as long-axis (e) T1W FS images; show large dorsal ulcer overlying the 5th MTP articulation (long white arrow on d). There is marked enhancing (black arrow on e) bone marrow edema (black arrow on b) of the M5 indicating presence of osteomyelitis. Note also remarkable dorsal skin and softtissue edema (twin short white arrows on a through d) as well as edema of the deep short foot muscles and its fatty infiltration on (black dotted oval on a & c) due to associated diabetic neuropathy and myopathy; respectively. © Radiodiagnosis, Alexandria University, Faculty of Medicine - Alexandria/EG
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Fig. 4: (a) AP oblique radiograph of the foot showing MTP and intertarsal joints, dislocation, erosions, destruction and disorganization indicating chronic neuroarthropathy. MR images of the fore- and mid-foot regions; sagittal (b) T2W FS, (c) pre-contrast T1W FSE as well as (d) post-contrast T1W FS and serial short-axis (e) T2W FS and (f & g) post-contrast T1W FSE as well as (h) long axis post-contrast T1W FS images; showing planter ulceration (short white arrows in b &c) under the dislocated MTP joints, underlying sinus tract (small black arrows in e) surrounded by enhancing softtissue tumefaction (phlegmon; seen in c & f) as well as tibial sesamoid enhancing (black circle in f) marrow edema (black circle in b &e) indicating sesamoidal osteomyelitis. The synovial sheath of the flexor hallucis longus is empty exhibiting contrast enhancement (thick white arrow in g &h) till tendon re-appears retracted within its sheath (thick white arrow in d) inferring infecting tenosynovitis and FHL tear. © Radiodiagnosis, Alexandria University, Faculty of Medicine - Alexandria/EG
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Fig. 5: MRI of the fore-foot; short axis (a) T2W FS, (b) post-contrast T1W FS as well as sagittal images (c) T2W FS, (d) T1W pre- and (e) T1W post- contrast images where an enhancing well- defined fluid collection is seen in the 1st interphalangeal space (open arrows in a through e) consistent with abscess formation. Enhancing soft-tissues over the dorsum of the fore-foot infers associated cellulitis (short white arrows in c through e). Note there was no altered bone marrow signal observed in this case defeating presence of osteomyelitis. © Radiodiagnosis, Alexandria University, Faculty of Medicine - Alexandria/EG
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Findings and procedure details Soft-tissue changes: Thinning of the plantar fat pads results in thin skin under pressure points, in the diabetic foot [2,3]. Then, abnormal mechanics over these pressure points beget hyperkeratosis with subsequent callus formation [4]. Callus: It commonly develops under the heads of first and fifth metatarsal heads (Figure-1)as well as plantar aspect of the big toe in ambulatory diabetics [4]. In bed-pound patients lying supine with external rotation of their feet these calluses develop over heel and lateral malleolus. Rarely these ulcers develop in the midfoot with the development of "rockerbottom" deformity due to charcot's arthropathy. On It exhibits a localized area of low signal intensity on T1W and low to intermediate signal on T2W images. On enhanced T1W images; it shows diffuse contrast enhancement like soft-tissue infections [5,6]. Skin ulcers and sinus tracts: Autonomic neuropathy; resulting in skin dryness and fissuring; coupled to unrecognized trivial trauma, usually aids breakdown of callus and results into skin ulceration [7]. When skin ulcers commences it is depicted as focal interruption of the skin line. Acute ulcers with granulation tissues emits water-like signal on different MR pulses (Figure-2) with gadolinium enhancement on post-contrast images [6]. Contrarily; chronic ulcers exhibits intermediate to low-signal of its base on T2W images inferring healing with fibrosis. Ulcers penetrating deeply (>2cm) will form sinus tracts (Figure-2) that serve as a route for subsequent spread of infection leading to deep soft-tissue abscesses and/ or osteomyelitic affections [5]. Sinus tracts appear as linear T2 hyper-intense soft-tissue signal with characteristic tram-track appearance on post-contrast T1W fat-suppressed images (Figure-2-d) [6,9].
Cellulitis, phlegmon and abscess formation:
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Cellulitis refers to non-necrotizing inflammation of the skin and subcutaneous tissues while sparing the muscles and deep fascial planes [9]. It presents clinically as localized pain, swelling and tenderness; common clinical findings shared with the soft-tissue edema accompanying diabetic neuropathy and ostearthropathy in this population. On MR; both conditions appear as skin thickening and reticular stranding of the subcutaneous tissues; low signal on T1W and high signal on T2W images. Following intravenous gadolinium administration, enhancement is common in cellulitis (Figure-3) while it may be non-appreciable in diabetic neuropathy and ostearthropathy[5, 6, 9]. Phlegmon is a more advanced stage where suppurative inflammation commences in the subcutaneous connective tissue yet no abscess has ensued [9]. On MR appears as an ill-defined mass in the subcutaneous tissues that exhibits low signal intensity on T1weighted images and intermediate to high (non-fluidal) signal intensity on T2-weighted images with vague variable enhancement on post-contrast images (Figure-4) [6]. When suppuration of the deep tissues gets localized, an abscess befalls. It appears as walled off fluid collection on MR images (Figure-5) i.e. T1W iso- or hypo- intensity and T2W hyper-intensity with rim enhancement on post-gadolinium T1 images [5,6]. Recognition of an abscess declares inevitable surgical debridement. Foreign body: Foreign body penetration is common in diabetic patient due to associated neuropathy. It appears as signal void structure in all pulse sequences with or without peripheral contrast enhancement according to surrounding inflammatory reactions (Figure-6) [10]. Diabetic tendinopathies: Spread of infection into the soft tissue with violation of fascial planes can results in infective tenosynovitis and may progress to tendon tear. It usually targets the flexor, peroneal and Achillis tendons. Variable MR signs denoting infection are seen as increased signal intensity of the tendon, indistinct margins, and fluid collections within its synovial sheath. However, the most specific sign is peritendinous enhancement of a tendon (Figure-2-e-to-i), traversing an area of adjacent soft-tissue infection; especially if ulcer exists [11]. Alternatively; especially in tendons without synovial sheaths e.g the tendon Achillis; degenerative tendinopathies commence and may end up with tendon tear. Diabetic myopathy:
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Diabetic motor neuropathy results in subacute muscle denervation followed by fatty muscle atrophy; especially in poorly controlled insulin-dependent diabetics [12]. The deep muscles of the foot are preferentially affected. In early disease no structural changes are perceived on MR. However; in the subacute stage (more than 2 weeks) muscle edema with effacement of the striated muscle feathery pattern may be seen; evidently seen on T2W and inversion recovery images (Figure-7). Later on, fatty muscle infiltrations commence progressing to muscular fatty atrophy best depicted as high signal on T1W images (Figures-3 & 4) [13].
Osteo-articular Changes: Charcot (neurosteo-) arthropathy: It is a progressive inflammatory mediated pathologic process that can target both softtissues and foot osteoarticular framework [14]. In the acute stage; pain, swelling, hotness and redness are the salient clinical features. With more progression of the disease, soft-tissue changes subside and structural deformities persist. These symptoms are commonly confused with osteomyelitis. Charcot's osteoarthropathy commonly involves the mid-foot joints i.e. Lisfranc's and Chopart's [6,15]. In early disease, MR shows joint effusions, marrow edema; especially in the subchondral zones; and soft-tissue edema (Figure-8) with variable contrast enhancement following intravenous contrast. With more disease progression and inadequate off-loading, further bone resorption occur, articular surface fragmentations commence with subsequent disorganization of the involved joints (Figure-4) and failure of the foot's longitudinal arch ending into rocker-button deformity [6,15-17]. Pedal osteomyelitis: Pedal osteomyelitis is commonly caused by contagious spread from an adjacent skin ulcer and/or cellulitis. Thanks to its excellent soft-tissue contrast and ability to depict bone marrow changes, MR is superior to other imaging modalities in early detection of diabetic foot soft-tissue and osseous changes [5,6,8,15]. MR changes of osteomyelitis are early detected by MR in contrast to delayed diagnosis on X-ray and lower specificity in scintigraphic studies [18]. Bone marrow changes are the most sensitive index of osteomyelitic affection. T1W is the most reliable image to detect osteomyelitis due to marrow edema replacing the normal high-signal of fatty marrow with remarkable marrow enhancement following contrast administration (Figures 2,3 &7) [19].
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Collateral bone marrow edema on water sensitive imaging is confirmatory. However, T2/ STIR marrow edema alone (Figures 1 & 6) is a sign of reactive osteitis that may be seen with charcot's neuroarthropathy, cellulitis and post-surgical interventions [6]. An important MR sign of osteomyelitis is described as the "ghost sign" (Figure-9) where the affected bone is well demarcated on T2W and post-contrast T1W images while the bony details disappear on pre-contrast T1W images [6]. Septic arthritis: Contagious spread of infection from soft-tissue and/or osteomyelitis foci to adjacent joint may occur in the diabetic foot resulting in septic arthritis. The targeted joint may show sub- and peri-articular marrow edema, complex effusion, and thickened synovium as well as enhancement following contrast administration (Figure-10) [5,20] .
Differentiating osteomyelitis from neuroarthropathy: Both pedal diabetic neuroarthropathy and osteomyelitis can show soft-tissue, subarticular and bone marrow edema on MR imaging. This makes clearing of infection a challenging task for the radiologist. However, simple tricks (Table-1) can help in differentiating both entities [5, 6, 16, 22, 23].
Table-1: Helpful MRI features to differentiate osteomyelitis from Charcot's arthropathy.
Difference
Charcot's arthropathy
Deformity
common along with bony Usually none unless there is debris an underlying neuropathic joint
Disease topography
Targets multiple bones and Localized to the affected joints bone and adjacent softtissues
Bone marrow
Peri- and sub- articular Involves a single bone distribution. Acute form: and exhibits high signal on mimics osteomyelitis. water-sensitive sequences and low on T1images with Chronic: normal marrow enhancement following IV signal or low on T1and T2 gadolinium.
changes
Osteomyelitis
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Soft-tissue changes
Intact overlying skin +/- Often present with overlying edema early ulcer, abscess or sinus tract
Infected versus non-infected neurosteoarthropathy: A triage of infected from non-infected neuropathic arthropathy is a continuous challenging task; both clinically and imaging wise. Overall, in a diabetic foot with neuropathic arthropathy; soft tissue fat replacement, fluid collections, and sinus tracts passing to a weight-bearing point with underlying area of extensive marrow edema are MRI features that obviously infer superimposed infection [16]. Skin ulcerations, post-contrast enhancement of the soft-tissues and fluid collections are not a guarantee for presence of superimposed infections [22]. Images for this section:
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Fig. 6: MRI of the hindfoot/Ankle region, sequential short-axis/coronal (a) pre-contrast T1W FSE, (b) PD FS; long-axis/axial (c) pre-contrast FS T1W, (d) post-contrast FS T1W; and (e) sagittal post-contrast FS T1W, showing a palm splinter impacted through a long sinus tract within the sustanaculum tali. The splinter appears as linear low signal on coronal and sagittal planes (black arrows in a & e), while it is rounded axial signal void on (open arrows in c &d). There is marked soft-tissue and bone marrow edema (black circle in b) with enhancement following contrast. No other soft-tissue changes are detected. Splinter extraction and follow-up confirmed absence of OM. © Radiodiagnosis, Alexandria University, Faculty of Medicine - Alexandria/EG
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Fig. 7: Serial Sagittal MR images of the big toe (a) T2W FS, (b) non-contrast T1W and (c) contrast-enhanced T1W showing plantar ulcer (small white arrow in a through c) underneath the big toe. There is stranding of the adjacent soft-tissue with enhancement indicating cellulitis, enhancing edema of the proximal phalanx of the big toe inferring osteomyelitis. Note the enhancing fluid collection (open arrows in a through c) on the dorsal aspect of the big toe due to abscess formation. © Radiodiagnosis, Alexandria University, Faculty of Medicine - Alexandria/EG
Fig. 8: MRI of the whole foot, sagittal (a) non-contrast T1W FSE and (b) T2W FS images; show marked edema of the subcutaneous tissues (small white arrows) of the foot dorsum with extensive marrow edema involving all tarsal bones as well as ankle and subtalar joint effusions (white dotted oval) with subluxation consistent with Charcot's arthropathy. Note downward descent of the cuboid "rocker-bottom deformity" (open arrow in a) that shows subarticular cystic changes (thin black arrow) ; a feature that rule out superimposed infection. © Radiodiagnosis, Alexandria University, Faculty of Medicine - Alexandria/EG
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Fig. 9: MR of the fore-foot; long axis (a) STIR, (b) T1W FSE pre- and (c) T1W FS postcontrast as well as short-axis (d) T2 FSE and (e) T1W FSE contrast enhanced images; show bone marrow edema of the little toe proximal phalanges as well as proximal M5 on T2W images (a) with their apparent dissolution on pre-contrast T1 (b) and well definition of their borders following their enhancement (c); what is called "ghost sign" (changes within the double-lined white oval). Note; edema (black arrow on d) and enhancement (black arrow on e) of the subcutaneous tissues' tumefactive thickening under the 5th MTP joint (d ) representing inflammatory phlegmon. © Radiodiagnosis, Alexandria University, Faculty of Medicine - Alexandria/EG
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Conclusion • •
•
Diabetic foot is a complex set of different pathologies; most of which can be confidently diagnosed with MRI. Individually tailored MRI examination; using a combination of watersensitive as well as T1W pre- and post contrast sequences is essential for comprehensive evaluation. Differentiating osteomyelitis from neuroarthropathy is challenging task, however still a lot of MRI features can triage both entities.
Images for this section:
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Fig. 10: MRI of the fore-foot (2nd ray), serial sagittal (a) T2W FS, (b) T1W FSE preand (c) post- contrast T1W FS images; show swollen 2nd toe with marked soft-tissue edema, subluxation of the proximal IP joint (arrow in a) and bone marrow edema of the 2nd ray middle phalanx (arrow in b). There was remarkable enhancement of the marrow, subluxed joint synovium and surrounding soft-tissues following contrast administration (black dotted circle in c). Features infer middle phalanx osteomyelitis, septic arthritis of the PIJ with surrounding soft-tissue phlegmon. © Radiodiagnosis, Alexandria University, Faculty of Medicine - Alexandria/EG
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