Imaging of Spinal Metastases after Percutaneous AblationTaylor J Greenwood, MD, Adam Wallace, MD, Aseem Sharma, MD, Jack

Jennings, MD, PhD

IntroductionSpine is the most common site of osseous metastatic disease and when symptomatic

presents with debilitating pain

Pain comes from periosteal stretching, inflammation, or tumor-related cytokines; exacerbated by spinal cord or nerve root neural

compression or pathologic fracture

First line for symptomatic metastases

-NSAIDS-Acetomenophen-Opioids

-High doses often required-Drowsiness, altered mental status and limits independence (no driving)

Analgesics

Treatment Options

Treatment Options

Cytotoxic and Targeted Therapy

-Improved survival-Side effects sometimes not tolerated-Pain relief variable, often takes weeks to months

Chemotherapy

Treatment Options

Conventional external beam radiation therapy-Partial (~60%) and complete (23%) palliation rates

Stereotactic body radiation therapy-May have better longer lasting pain and tumor control

Radiation

Treatment Options

Spine Instability Neoplastic Score (SINS)

Considers:-Location-Bone quality-Alignment-Vertebral compression-Posterior involvement -Higher scores = greater instability-Surgical consultation for scores >7 or neural compression

Surgical

Percutaneous Management of Spinal Metastases

Transpedicular approach using

fluoroscopy or CT guidance

Radiofrequency, microwave or

cryoablation is used to cause tumor

necrosis

Vertebral augmentation

stabilizes pathologic fractures

Effective palliation when analgesics are ineffective or

not tolerated

Effective after

radiation has been

exhausted

Systemic chemotherapy does not need to be stopped

Pain relief often

immediate

Imaging for Treatment Planning

CT Cortical integrity

Posterior vertebral wall

Pedicle medial cortex

Tumor may retract,Osseous canal stenosis

will not

When intact: it is a firm backstop during transpedicular acces

Imaging for Treatment Planning

CT Cortical integrity

Posterior vertebral wall

Pedicle medial cortex

Imaging guidance for small or posterior lesions

MRI Shows full extent of

tumor within the vertebral

body Epidural and

foraminal extension

Imaging for Treatment Planning

MRI Shows full extent of

tumor within the vertebral

body Epidural and

foraminal extension Reveals tumor at

adjacent levels

Imaging for Treatment Planning

Pain cannot be localized to a single level when contiguous

levels are involved.MRI changed management to a 2

level procedure ?

Evolving Zone of AblationL1 pathologic compression fracture from metastatic breast cancer treated with radiofrequency ablation (RFA) At 1 week: Vertebral body

has diffuse edema and hyperemia but ablation zone is non-enhancing.

At 3 months: Thin T2 dark, enhancing rim of granulation tissue and hemorrhagic congestion is seen at ablation zone margin. Ablation zone is nonenhancing T2 hyperintense area. Signal void is from vertebral augmentation cement (*).

STIR STIR

T1 FS C+T1 FS C+

**

Before After

1 week 3 months

Margin of EnhancementL3 metastatic renal cell carcinoma treated with stereotactic radiation followed 10 months later by RFA Lytic metastasis has central non-

enhancement consistent with tumor necrosis centrally and viable tumor peripherally

At 2 months after RFA: Paraspinal muscle inflammation is seen, likely from the percutaneous ablation. There is mild residual hyperemia of the vertebral body and signal void from cement. T2 hyperintense smoothy enhancing margin was stable for > 1 year, therefore likely granulation tissue.

Granulation response can be variable in thickness, smooth contour favors fibrosis

T2

T1 FS C+

T2

T1 FS C+

Before After

2 months

Margin of Enhancement

In contrast to the previous example . . .

L1 small cell lung cancer metastasis treated with RFA Zone of ablation is

non enhancing but nodular enhancing soft tissue outside the zone of ablation has increased, indicating residual tumor

Salvage Radiation Therapy resulted in tumor retraction

*

*

T1 FS C+

T2T2

T1 FS C+

Pre-Tx 2 months

Cryoablation

Painful sclerotic hypermetabolic L4 metatastatic non-small cell lung caner treated with cryoablation

CT is useful to see the low attenuation “ice ball” in the paraspinal soft tissues but cannot be seen within the compact cancellous bone of the vertebral body.

CO2 gas in the epidural space injected through the subjacent neuroforamen helped prevent neural injury.

Patient reported complete pain relief

Tumor Recurrence

MRI 10 months after cryoablation showed tumor recurrence Ablation tract and T2

dark rim of hemorrhagic congestion are clearly seen

Nodular enhancement is seen within the ablation zone and in the right psoas muscle

T2 dark enhancing marrow is due to the blastic metastasis

Axial T1 FS C+ T2

Sag T1 FS C+ T2

Imaging Correlation

S4 rectal cancer metastasis treated with cryoablation CT guidance shows the “ice

ball” delineating the ablation zone.

At 4 months: MRI and PET/CT correlate with the original ablation zone

Central T1 hypointense, T2 hyperintense coagulation necrosis with T2 hypointense, T1 hyperintense rim of hemorrhagic congestion is seen just like RFA

PET/CT shows no uptake in the ablation zone, but disease progression was seen at contiguous levels

Cryoablation Sag T2

Axial T1 FS Pre-C PET/CT

*

*

Post contrast images show tumor enhancement at S3 and necrosis from ablation

at S4

Diffusion Weighted Images

DWI can be helpful adjunct tool in evaluating post treatment changes from tumor. Particularly if contrast in

contraindicated and tumor restricted initially

Coagulation necrosis has rapid diffusion (relatively lower high b value signal and increased ADC)

Metastases often have restricted diffusion

DWI

ADC

S3 No Tx S4 s/p cryoablation

T2T1 FS C+

Pitfall: T1 hyperintensity

Sacral rectal cancer metastasis 1 month after RFA. T2 heterogeneous,

T1 hyperintensity within the ablation zone: hemorrhage or tumor?

Subtraction images are helpful in differentiating residual tumor from hemorrhage.

T1 FS C+

T2 FS T1

CTSubtraction

PET/CTOligometastatic Ewing’s sarcoma to L4 treated with RFA Follow up PET/CT 3 weeks after

RFA showed residual hypermetabolic lesion

Despite attempted retreatment tumor progression was seen 2 months later Patients symptoms also

returned

Baseline 3 weeks later

2 months after 2nd RFA

2nd RFA

PET/CT can detect residual hypermetabolic

disease before symptoms return and

helps differentiate tumor from granulation tissue

Tumor or Fibrosis?

L5 = RFA treated lesion with marrow fibrosisL4 = viable metastatic disease

Tumor

Fibrosis

T1 T2 T1 FS C+PET/CT

When to Biopsy

1 month 11 months

3 months

8 months

L4 leiomyosarcoma metastasis treated with RFA. Images show gradually increasing enhancement surrounding the ablation cavity. Patient developed recurrent back pain. PET/CT was performed just prior to biopsy. Final Pathology: Marrow Fibrosis

When clinical and imaging parameters are discordant, percutaneous biopsy should

be considered before re-treatement.

Summary

Post Ablation changes evolve over the first several months due to an inflammatory response

Margin of Enhancement: Thin, smooth = expected treatment change Thick or increasing enhancement does not always

equal tumor When clinical and imaging parameters are

discordant, biopsy should be considered before re-treatment.

PET/CT and DWI are useful in evaluation of residual or recurrent hypermetabolic disease.