SARELGAURMD
Interventional Radiologist
MR Forefoot R/O Osteomyelitis
Goal of study is to r/o osteo, usually in a diabetic patient with foot abnormality
Study is preferably done noncon, usually has to be done noncon as pt. has low GFR and can't take gad
it will be multiplanar T1W and FST2W set of images.
How to interpret:
1. FIND THE SOFT TISSUE ULCER. Can use coronal (looking on short axis of toes / MTs) and also use sagittal to trace out the soft tissue defect or ulcer. Look for loss of normal subQ fat. COMMON PLACES: 1st MT, Heel (Calcaneus), and 5th MT. THESE ARE 90% OF SOFT TISSUE ULCER LOCATIONS.
2. EVALUATE THE UNDERLYING MARROW SIGNAL ABNORMALITY: Remember, osteoMYELITIS is abnormality centered in the marrow, not cortex. Look for cortical erosion / osteitis but focus more on the underlying marrow abnormality. What is definitive osteo?- Blacked out / well defined homogenous T1W LOW signal, corresponding area should be high signal on T2WFS. If just see high signal on T2WFS without corresponding T1 low (well defined and homogenous / "blacked out" appearance), the finding likely reflects "reactive marrow edema". Acc. to YE, can give likelihood for osteo, such as low prob for osteo, high suspicion for osteo.
3. Look for coexistant cellulitis by looking at skin and subq tissue for high fluid signal, this should enhance if post con is done (enhancing edema)
4. Other findings often seen in a diabetic with osteo: fatty infiltration of the muscles with high T2W signal corresponding to chronic neuropathy or disuse.
5. De novo diagnosis of suspected osteo: MR is good. If doing a FOLLOW UP MR (after tx with IV abx) to see if osteo is resolving / resolved, then MR is not so good. Acc to YE, marrow signal abnormalities can persist for 1 yr following diagnosis of osteo. therefore, if you see abnormality, could be healed, and vice versa, if see no abnormality, could still be osteo.
YE finding following article helpful:
MR Ankle Search Pattern (YE Method)
Evaluate Tendons:
Post Tib and Ant Tib most likely to tear
Need to know the insertions, PTT tears at malleolus, ATT tears at the INSERTION (almost missed ATT insertional tear)
Eval all tendon groups, use AXIAL images for this
Flexor, Extensor and Peroneal groups
Then eval the ligament structures:
Syndesmotic ligaments on Axials
ATFL and PTFL on Axials
Use Coronal for deltoid
Can use coronal for CFL and PTFL if not well seen on axials
Check achilles tendon and plantar fascia on Sagittal, plantar fascia can have significant findings so don't forget
Check joints:
First ankle joint aka tib-talar joint, look for cartilage disease, OCD
Then move to subtalar joint, 3 facets, need to review this anatomy, can find coalitions at this point
Do midfoot joints and intertarsal joints, looking for cartilage abnormality
Eventually finish with muscles, nerve regions, and subq tissue
Remember to check Tarsal tunnel and sinus tarsi for ?? not sure yet
**WORK IN PROGRESS**
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MR Knee Search Pattern
Re. MR sequences to use:
-acc. to prominent book, can see all meniscal tears on sagittals only
-may not need coronal T1 or PD weighted images
-use T2W coronals to eval meniscocapsular seperation by seeing fluid between two structures
What to use for what:
-Sag PD and T2W for eval of menisci
-Coronal for eval of medial and lateral supporting structures
-Axials to eval patellar and trochlear cartilage
Basic overview of search pattern:
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Check menisci on sagittal PD and FST2W
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Check ACL and PCL on Sagittal PD and FST2W or dedicated ACL sequence
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Check MCL on Coronal
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Check LCL on Coronal: This includes true LCL, biceps femoris tendon, and ITB (check ITB for ITB friction syndrome)
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Posterolateral corner (only semi emergency finding in Knee MR): arcuate ligament and popliteofibular ligament:
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Basically check the fibular head, posterolateral corner injury: LCL injury in assoc. with popliteus tendon, arcuate ligament, popliteofibular ligament, and ACL or PCL
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Extensor mech (patellar tendon, patella, quad tendon): on sagittal and axials. R/o possible patellar dislocation, check medial and lateral retinanculum
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Check for joint effusion and Baker's Cyst (semimemb, medial gastroc), and Pes bursa (goose foot, S-G-T)
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Cartilage: Check medial, lateral compartments on Coronal or sagittal or both. Check patella-trochlear compartment on Axials
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Bones: Check for marrow edema/contusion or cortical disruption
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Muscles: Check for atrophy or edema.
Menisci:
-look for abnormal signal (dark normal, bright / fluid is abn) extending to articular surface
-intrasubstance signal is often seen, related to degeneration
-acc to books, 10% error rate for meniscal tears
-if acl is torn, meniscal tear associated
-how to describe tear: location, extent, which surface, assoc cyst, displacement or fragmentation
-2 or more body segments, think discoid meniscus, this can be well eval on coronal images
-acc to YE, remember to look for truncation of the meniscus to suggest prior surgery, can also look to see if arthroscopic ports and secondary fibrosis see in the intraarticular fat pads
-severe intrasubstance degeneration can turn into meniscal cyst which can be missed at arthro, when the cyst is expressed into the parameniscal region during weight bearing, called parameniscal cyst
Cartilage:
-cartilage tears can be extremelly subtle
-don't want to miss delaminating tears ie tears that undercut the cartilage plate, as this can cause the cartilage to break off and become an intraarticular body
-almost missed a tear on the inner lateral femoral condyle, use T2WFS images to look for fluid cutting into the cartilage
Knee MR CAN'T MISS LESIONS:
meniscal tear (a real one)
displaced cartilage defect / delamination (can be extremely subtle so trace T2WFS images with fine tooth comb)
ACL tear
??
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MR Shoulder Search Patterns:
Anatomy:
great anatomy website- Freita's rad
CAN'T MISS LESIONS:
-SST tear displaced
-Labral tear (hard to differentiate from normal)
-Subtle Hill Sachs (look on axial at Post-lat HH)
-??