MRI for Diagnosis of MSK Tumors

Seul Ki Lee

Department of Radiology, St. Vincent’s Hospital, The Catholic University of Korea, South Korea

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Qualitative and Quantitative Analysis for Tissue Composition

Imaging modalities for MSK tumors

Imaging modalities for MSK tumors

• Plain radiographs and CT scans
• Bone involvement

Angiosarcoma of bone

• Mineralization

Synovial sarcoma

Imaging modalities for MSK tumors

• Ultrasound
• Cystic vs. Solid

• Vascularity

Synovial sarcoma

Pseudoaneurysm

Workup of soft tissue mass

Surg Clin N Am 100 (2020) 669–680

Soft tissue mass

Small, slow-growing, mobile

Ultrasound

Solid, rapid growing, fixed, deep

MRI + contrast

Non-lipoma

Lipoma

MRI protocol

MRI + contrast

MRI protocols for MSK tumors

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• Conventional sequences: T1WI, T2WI, T2 fat suppression (fluid sensitive seq), T1 contrast enhancement + fat suppression

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• Axial & longitudinal - coronal (mediolateral) or sagittal (anteroposterior)
• FOV? Small (resolution of tumor ↑) vs. Large (anatomic coverage ↑)

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• Advanced sequences (selective): diffusion-weighted image (DWI), dynamic contrast enhancement (DCE), IVIM, spectroscopy, DTI, etc…

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Tissue composition on MRI scans

MRI – Tissue composition

Lipoma

[Mature fat component] Absolute benign case

MRI – Tissue composition

[Mature fat component] Absolute benign case

Intraosseous lipoma

MRI – Tissue composition

[Pure fluid component] Absolute benign case

Ganglion cyst

MRI – Tissue composition

[Pure fluid component] Absolute benign case

Intraosseous ganglion cyst

Absolute benign cases by Tissue composition

The MRI features are sufficiently specific to allow a histologic diagnosis in a small number of pathologic conditions. Most lesions are lack of sufficient specificity at MRI for enabling a diagnosis. (rec) biopsy

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• Lipoma: T2 high, T1 high, + fat suppression (+)

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• Cyst: T2 high, T1 low (variable) + fat supp (-) + thin rim enhance

MRI – Tissue composition

• Lipoma vs. hematoma?

T1 and T2 both high SI

No enhancement

Fat suppression (using water and fat only)

Atypical lipomatous tumor

Hematoma

Fat suppression (using water and fat only)

T1 hyperintense mimicker, hematoma

• SI characteristics of hematoma on MRI

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• Confirm presence or absence of enhancement by post-contrast subtraction image or non-contrast T1 fat suppression image.

hematoma

MRI – Tissue composition

• When shouldn’t I call it a cyst?

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T2 high SI

Thin wall enhancement

T2 shine through effect

T2 shine through effect

Neurogenic tumor

(myxoid tumor)

MRI – Tissue composition

• When shouldn’t I call it a cyst?

Homogeneously T2 high SI

wall enhancement

T2 shine through effect

T2 shine through effect

Myxoma

MRI – Tissue composition

• When shouldn’t I call it a cyst?

T2 high SI

wall enhancement

T2 shine through effect

T2 shine through effect

Metastatic lymph node with necrotic change

T2 hyperintense mimicker, pseudocystic

• Myxoid tumors:
• T2WI: near-fluid SI
• Thin septal enhancement & heterogeneity on T1 and T2WI
• Ganglion cyst: periarticular area (synovial line, bursa, joint recess, fibrocartilages, periosteal, traumatic, surgical seroma..)

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• Necrotic change of malignant solid tumors:
• T2WI: near-fluid SI
• Thick and nodular enhancement & heterogeneity on T1 and T2WI
• Perilesional edema

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• Synovial sarcoma, vascular tumor, chondroid tumor

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Myxoma, neurogenic tumor, myxoid sarcoma (myxoid liposarcoma, myxoid fibrosarcoma)

Any mass with non-specific MRI features

Any mass with non-specific MRI features

• Iso T1 and heterogeneously high T2: non-specific MRI appearance

🡪 referral to specialized tertiary care center

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• Narrowing the differential diagnosis!
• Specific location: scapular elastofibroma dorsi, plantar fibroma, subungal glomus tumor, intermetatarsal Morton’s neuroma, Achilles xanthoma, abdominal wall desmoid tumor, neurogenic tumor, dermatofibrosarcoma protuberans, etc..
• Many signs: neurogenic tumor (target sign, fascicular sign, entering/exiting nerve sign), myxoma (bright cap sign), myositis ossificans (zonal phenomenon), synovial sarcoma (triple sign, bowl of grapes), myxofibrosarcoma (tail sign), etc..
• Containing T1, T2 low SI foci: tenosynovial giant cell tumor (d/t hemosiderin), fibrous tumor (fibromatosis, elastofibroma, fibrosarcoma), chondroid/osteoid tumor, crystal deposition disease, etc..

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Any mass with non-specific MRI features

• Iso T1 and high T2: non-specific MRI appearance

🡪 referral to specialized tertiary care center

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• Findings with increased risk of malignancy
• Depth: deep to the fascia
• Size: > 5 cm
• Location: proximal lower extremity, retroperitoneum
• T1: signal heterogeneity
• T2: signal heterogeneity
• Post-contrast T1: heterogeneous enhancement or necrotic change
• Margin: ill-defined
• Peritumoral edema: presence
• DWI: diffusion restriction in solid mass (low ADC <1.1x10^-3mm²/sec)
• DCE: malignant perfusion pattern with early arterial enhancement

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Biopsy

• Indications: any mass for which imaging is no definitive
• Equipment depends on target lesion

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Radiol Clin North Am 2008 Gogna

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Bonopty® 14G - AprioMed

Biopsy

• Planning the biopsy
• Biopsy track to be included in surgical specimen
• Biopsy should not violate more than on compartment
• Biopsy the soft tissue component of a bone lesion if present

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• Imaging guided-biopsy
• Avoid vital structures
• Select the most appropriate part of the lesion
• Target location with highest yield
• Select a path that will be excised along with the tumor
• Avoid contaminating compartments
• Beware of bloody lesions: RCC, osteosarcoma, hemangioma

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Advanced role of functional MRI for MSK tumors

Dixon technique (phase-contrast tech.)

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Advantages:

• (3-point) Lesser sensitive to B₁ and B₀ heterogeneity than fat saturation 🡪 homogenous fat suppression (metallic implant, head/neck, or lung apices)
• Higher SNR than STIR
• Added to T1WI (enhanced), T2WI, and PDWI
• A single-image acquisition, w/ and w/o fat suppression
• Fat quantification

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Dixon method Questions and Answers in MRI

Dixon and MSK tumor

• Quantification of fat
• Zajick et al.: a 20% decrease in SI on the opposed-phase images relatively to that on the in-phase imaging
• Spine bone marrow lesion or compression fracture; true marrow-replacing tumor vs. infiltrative process such as edema, red marrow hyperplasia..
• Opposed-phase에서 SI drop이 있는 경우는 fat이 존재하는 것으로 benign에 가깝다.

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• Fat fraction values were calculated with the following formula:
• % signal drop = (SI IP – SI OP ) / 2SI IP × 100

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Marrow lesion

(metastasis vs. felon)

malignant

benign

Mean 679.5 Mean 854.1

T2 FS

T1 in

T1 out

Breast cancer bone metastasis

T2 FS

T1 in

T1 out

Mean 975.5 Mean 135.9

Animal bite OM

Diffusion-weighted image

• Quantification of cellularity
• Signal losses on DWI are proportional to both the free motion of water molecules and the diffusion gradient strength.
• When diffusion is high, the return to phase is incomplete and spins are out of phase.
• In hypercellular lesions, diffusion is restricted, the spins are poorly mobile and return to phase.
• DWI should be assessed visually, comparing between a low b-value image and a high b-value image.
• The difference in signal between these two images is related to water diffusion, often termed the ADC.

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KCR 2020

DWI and MSK lesions

In tumorous conditions, DWI typically shows low ADC values in malignant aggressive tumors, while benign tumors usually exhibit high ADC values.

* DWI has also been shown to be effective in detecting abscesses containing protein-rich, epidermal inclusion cyst containing viscous liquid as restricted diffusion

Diffusion restriction

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DWI: quantification of cellularity + heterogeneity

Dynamic contrast-enhanced MRI

• Malignant lesion:
• incomplete vascular endothelial cells and high vascular permeability 🡪 increase the leakage of contrast agent

• hypervascularity with frequently associated with microscopic necrotic change 🡪 weaken the power of V_e

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• Compounding effect of K^trans and V_e may be the main reason for better correlation between quantitative parameter of K_ep & histology of microvessel density

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• iAUC: combined influence of blood volume, flow, and permeability, but is likely dominated by blood volume

K^trans

V_e

K_ep =

K^trans, volume transfer contast (permeability);

V_e, extracellular space per unit volume of tissue;

K_ep, rate constant (ratio of K^trans and V_e)

SK Lee et al. Oral presentation @ RSNA 2018

Initial

DCE-MRI

Time intensity curve

KCR 2017

DCE: Quantification of perfusion

Conclusion

Conclusion

• MSK tumors are a complex and heterogeneous group of tumors.

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• Narrowing the differential diagnosis by tissue composition

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• Addition of functional sequences to the conventional MRI protocols increases the diagnostic accuracy of interpretations for MSK tumors

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Thank You

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