Accuracy of magnetic resonance imaging in planning the osseous resection margins of bony tumours in the proximal femur: based on coronal T1-weighted versus STIR images

Accuracy of X-Ray and Magnetic Resonance Imaging in Defining the Tumor Margin in Primary Bone Sarcoma

BACKGROUND

Limb-salvage surgery for primary bone sarcomas are preceded by X-ray and MRI for surgical planning. However, the accuracy of X-ray and MRI predicted margins are not well described. Our study examined these questions: (1) How accurately do X-ray and MRI margin measurements reflect the true margin on pathology reports? (2) Do X-ray or MRI margin measurements have smaller differences compared to pathology reports? (3) How many X-ray or MRI margin measurement differences were greater than 1 cm, 2 cm, and 3 cm from pathology reports? (4) Is there an X-ray or MRI view that consistently results in a smaller difference from pathology reports?

METHODS

This retrospective chart review examined patients with primary bone sarcoma treated with limb-salvage surgery. Reviewers used electronic measurement tools to determine margins from X-ray or MRI based on the resection length of the pathologic specimen. Mean differences of margin measurements to pathology reports were calculated. We determined outliers of imaging margin measurements at 1 cm, 2 cm, and 3 cm differences to pathology reports.

RESULTS

In the total cohort of 39 patients, the mean difference of X-ray and MRI margins compared to pathology reports were 1.09 cm (st dev 0.79 cm) and 0.71 cm (st dev 0.70 cm), respectively. MRI margin measurements had smaller differences compared to pathology reports than X-ray in 32 of 38 cases (84%) with complete imaging. X-ray outliers at 1 cm, 2 cm, and 3 cm differences were 36, 14 and 2 respectively for 70 margin measurements and MRI outliers at 1 cm, 2 cm, and 3 cm differences were 17, 6, and 0 respectively for 66 margin measurements. The views with the smallest difference were anterior-posterior X-rays and MRI views with the closest predicted margin.

CONCLUSION

Electronic MRI margin measurements with the closest predicted margin provided the smallest differences with pathology reports and are therefore the most accurate for preoperative planning. When there is adequate residual diaphysis for reconstructive fixation, surgeons should plan for a 3 cm bone margin using MRI measurements to ensure complete removal of the intramedullary extent of sarcoma.Level of Evidence: IV.

Assessment of Resection Margins in Bone Tumor Surgery

Limb salvage surgery is now the preferred procedure for bone tumor surgery. To decrease the risk of local recurrence, it is crucial to obtain adequate resection margins. The obtained margins must be evaluated postoperatively because they influence what treatment is given subsequently when margins are not adequate (e.g., surgical revision and radiotherapy). The study aims to evaluate margin assessment of tumor specimen by MRI compared to conventional histology (to establish the viability of using MRI) and assess the accuracy of a patient-specific instrument when narrow margins were aimed. The resection margins in 12 consecutive patients that were operated on for bone tumor resection were prospectively analyzed using three methods: MRI of the resection specimen, macroscopic evaluation of specimen slices, and microscopic pathological evaluation. The assessments were qualitative (R0, R1, and R2) and quantitative (distance in mm). MRI, macroscopic, and microscopic margins generated similar results for both the qualitative (all resections were R0) and quantitative assessments. The median error in safe margins was 2 mm with a surgical guide (PSI) and 5 mm without a surgical guide. Local recurrences were not detected after a mean follow-up period of 3.7 years (range, 2.1-5 years); however, four patients died during the study. In conclusion, MRI is a valuable tool for assessing safe margins. When specimens are not available for pathological assessment (e.g., extracorporeally irradiated autograft or autoclaved autograft), MRI could be used to evaluate margins. In particular, when tumor volume is high, MRI could also help to focus the pathological examination on areas of concern.

Determination of skeletal tumor extent: is an isotropic T1-weighted 3D sequence adequate?

OBJECTIVES

To test the hypothesis that an accelerated, T1-weighted 3D CAIPIRINHA SPACE sequence with isotropic voxel size offers a similar performance to conventional T1-weighted 2D TSE (turbo spin echo) for the evaluation of bone tumor extent and characteristics.

METHODS

Thirty-four patients who underwent 3-T MRI with 3DT1 (CAIPIRINHA SPACE TSE) and 2DT1 (TSE) were included. Sequence acquisition time was reported. Two radiologists independently evaluated each technique for tumor location, size/length, tumor-to-joint distance, signal intensity, margin/extraosseous extension, and signal-to-noise (SNR) and contrast-to-noise (CNR) ratios.

RESULTS

Tumors were located in long (20/36, 55.5%) and pelvic (16/36, 44.4%) bones. 3DT1 sequence required an average acquisition time of 235 s (± 42 s, range 156-372), while two plane 2DT1 sequences combined (coronal and axial) had an average acquisition time of 381 s (± 73 s, range 312-523). There was no difference in the measurements of tumor length and tumor-to-joint distance (p = 0.95) between 3DT1 and 2DT1 images. Tumors were hypointense (17/36, 47.2% vs 17/36, 47.2%), isointense (12/36, 33.3% vs 12/36, 33.3%), or hyperintense (7/36, 19.4% vs 7/36, 19.4%) on 3DT1 vs 2DT1, respectively. Assessment of tumor margins and extraosseous extension was similar, and there was no difference in tumor SNR or CNR (p > 0.05).

CONCLUSIONS

An accelerated 3D CAIPIRINHA SPACE T1 sequence provides comparable assessments of intramedullary bone tumor extent and similar tumor characteristics to conventional 2DT1 MRI. For the assessment of bone tumors, the isotropic volume acquisition and multiplanar reformation capability of the 3DT1 datasets can obviate the need for 2DT1 acquisitions in multiple planes.

KEY POINTS

• 3DT1 offers an equivalent performance to 2DT1 for the assessment of bone tumor characteristics, with faster and higher resolution capability, obviating the need for acquiring 2DT1 in multiple planes. • There was no difference in the measurements of tumor length and tumor-to-joint distance obtained on 3DT1 and 2DT1 images. • There was no difference in signal-to-noise ratio (SNR) or contrast-to-noise ratio (CNR) measures between 3DT1 and 2DT1.

Pelvic bone tumor resection: what a radiologist needs to know

Pelvic bone tumors present a diagnostic and therapeutic challenge. Due to the deep anatomic location and resultant late clinical presentation, pelvic bone tumors tend to be large and located in close proximity to pelvic viscera as well as vital neurovascular structures. Operative management of pelvic bone tumors is indicated for a variety of orthopedic oncologic conditions. In general, limb-sparing pelvic resection rather than hemipelvectomy with amputation of the ipsilateral limb is considered when a functional limb can be preserved without compromising the surgical margins. There are various options for pelvic resection and reconstruction, and the selection depends on tumor histology, anatomic location, and extent. The decision regarding choice of surgical procedure and reconstruction method for a pelvic bone tumor requires a thorough knowledge of the pelvic anatomy, and careful inspection of the anatomic extent. The surgical plan must strike a balance between acceptable functional outcome and acceptable morbidity. In this review, we describe the different types of pelvic resection techniques, and the vital role preoperative imaging plays in defining the anatomic extent of a pelvic bone tumor and subsequent surgical planning.

MRI examination of resected malignant bone tumor can be an option for assessment of the osseous surgical margin

OBJECTIVE

Confirming the surgical osseous margin of a resected malignant bone tumor macroscopically before reconstruction with a prosthesis is ideal. However, making the cut-surface of the femur specimen during surgery is difficult because of the hard bone tissue. In order to resolve this problem, the possibility of intraoperative MRI was considered.

METHODS

MRI was performed at the surgical unit for five malignant femoral bone tumors that included two osteosarcomas and one undifferentiated high-grade sarcoma, and two metastatic tumors immediately after the tumor resection. The specimens were prepared in plastic containers with saline.

RESULTS

The osseous surgical margins were confirmed to be those planned pre-operatively in all cases without metal-induced artifacts. The T₁ weighted image (WI) was useful for evaluation of the osseous surgical margin, whereas the T₂WI was useful for confirmation of extraosseous soft-tissue.

CONCLUSION

The MRI was performed post-operatively as a preliminary evaluation of the technique. However, a limited sequence (i.e. coronal T₁WI) with short examination time could be performed during surgery for the sole purpose of assessing the osseous margin.

ADVANCES IN KNOWLEDGE

MRI examination of a resected malignant bone tumor specimen has not been reported, and can be an option for assessment of the osseous surgical margin.

Systematic review on the utility of magnetic resonance imaging for operative management and follow-up for primary sarcoma-lessons from extremity sarcomas

Primary sarcomas of the vertebral column affect roughly 5 in every million persons annually, of which half to one-third are malignant. Treatment of these lesions requires multimodal management, often employing attempts at en bloc resection of the lesion with negative margins. This may be facilitated using magnetic resonance imaging for preoperative margin planning, but current literature is lacking regarding the use of such imaging to accurately predict planned surgical margins. Here we review prior studies describing the use of magnetic resonance imaging for en bloc resection of sarcomas of the extremities to identify learning points for application to the treatment of spinal neoplasms. We conducted a systematic review of the PubMed and EMBASE literature. Included studies described the accuracy of MRI for preoperative evaluation of tumor margins, intraoperative guidance for en bloc resection, or post-operative evaluation of residual or recurrent disease. All included studies described patients treated for osseous or soft tissue sarcoma of the limbs. We found 1,705 unique references of which 27 met criteria for inclusion. Seven studies reported MR had an overall diagnostic accuracy of 93.6-96% for preoperative margin evaluation with non-contrast T1 most accurately reflecting true margins. In the nine articles reporting results of MR-guided resection, negative margins were achieved in 88.8-100% of cases with a closest margin of 2-4 mm. Eleven articles combined reported the accuracy of MR for residual disease or local recurrence, with a mean sensitivity and specificity of 71.7% and 79.3%, respectively for residual disease and 87.9% and 85.9%, respectively for local recurrence. The current literature for appendicular musculoskeletal sarcoma suggests that MR is highly accurate for defining tumor margins preoperatively, guiding osteotomy cuts intraoperatively, and documenting recurrence or residual disease. Further evidence is necessary to evaluate the degree to which it can accurately guide osteotomy planning for en bloc resection of vertebral primaries.

Inter-rater Variability in the Interpretation of Pre and Post Contrast MRI for Pre-Surgical Evaluation of Osteosarcoma in Long Bones in Pediatric Patients and Young Adults

BACKGROUND AND OBJECTIVES

The value of gadolinium enhanced magnetic resonance imaging (MRI) sequences for extremity osteosarcoma resection planning is unverified. We evaluate the performance of intravenous gadolinium enhanced MRI for identification of neurovascular bundle involvement (NBI) and intraarticular extension (IAE) in patients with osteosarcoma.

METHODS

Two pediatric radiologists independently analyzed MRI examinations of patients with pathology proven extremity osteosarcoma for NBI and IAE. Initial evaluation utilized only non-contrast MRI images (PRE) and, after 2 weeks, subsequent evaluation included both the pre and post contrast images (POST). Cohen's Kappa and McNemar's test were calculated to assess agreement between PRE and POST image interpretations of NBI and IAE.

RESULTS

56 patients with 90 preoperative MRI examinations were analyzed. PRE and POST interpretations were rarely discordant; 4/90 cases for NBI (Kappa 0.91) and 2/90 cases for IAE (Kappa 0.95). McNemar's test did not show a difference between PRE and POST imaging (NBI p=0.62; IAE p=0.48).

CONCLUSION

No significant difference between PRE and POST image interpretation was found. A high level of agreement between PRE and POST image interpretation suggests that pre-contrast MRI may be sufficient for pre-surgical planning for pediatric patients with long bone osteosarcoma.

Magnetic Resonance Imaging for the Assessment of Long Bone Tumors

Background:

Wide resection margins of osseous tumors are associated with a low incidence of local recurrence, making accurate measurement of the intraosseous extent of primary malignant long bone tumors is crucial. We compared the intraosseous tumor extent assessed by magnetic resonance imaging (MRI) with the gross specimen to evaluate the accuracy of MRI.

Methods:

A total of 255 patients with primary malignant tumors in the long bones were included. Using MRI, we defined the length of tumor as the distance from the articular surface to the boundary between abnormal and normal marrow signal. The extent of the abnormal intraosseous signal was measured on unenhanced T1-weighted (T1WI) magnetic resonance images after chemotherapy. All gross surgical specimens were sectioned, and tumor extent was measured. Wilcoxon signed-rank test was used to test the differences between MRI and gross specimen findings. Spearman's correlation analysis was used to test the correlation between groups.

Results:

Median tumor length by gross specimen (112 mm; range, 45–300 mm) was longer than that by MRI (108 mm; range, 45–304 mm; Z = −6.916, P < 0.001). Of 255 images, tumor length was accurately represented on 27 T1WI magnetic resonance images, overestimated on 79 images, and underestimated on 149 images. The median difference between imaging and gross specimen measurements was 2.0 mm (range: 1.0–15.0 mm) for the 79 cases where tumor length was overestimated, and 5.0 mm (range: 1.0–18.0 mm) for the 149 cases where tumor length was underestimated. The Spearman correlation demonstrated a high correlation of tumor length on gross specimen with the tumor length on MRI (R = 0.99, P < 0.01).

Conclusions:

We conclude that preoperative MRI could be a useful method in determining intramedullary malignant bone tumor boundaries and may serve as an accepted assessment method of long bone tumors before limb-sparing surgery.

Evaluating the Scope of Malignant Bone Tumor Using ADC Measurement on ADC Map

BACKGROUND

It is very important for surgeons to know the accurate borders of malignant bone tumors before they can precisely resect the tumors. The objective of the study is to investigate the usefulness of apparent diffusion coefficient value for estimating the extent of malignant bone tumor.

METHODS

VX2 tumor fragments were implanted into the tibiae of 30 rabbits. After 4 weeks, magnetic resonance plain scans were performed and then tumor specimens were cut into sagittal sections and partitioned into histology slices for dot-to-dot comparisons with microscopic findings. The sizes of the tumors measured separately on specimen, conventional magnetic resonance imaging sequences, and diffusion-weighted imaging (by measuring apparent diffusion coefficient value on apparent diffusion coefficient mapping) were compared statistically with each other.

RESULTS

The mean tumor sizes measured on specimen and apparent diffusion coefficient mapping (by calculating apparent diffusion coefficient value) were 5.20 ± 0.89 cm and 5.31 ± 0.87 cm, respectively; there was no significant difference between the 2 ( P > .05). The tumor sizes measured on T1WI, T2WI, T2WI with fat suppression were 4.82 ± 0.87 cm, 5.58 ± 0.87 cm, 5.63 ± 0.85 cm, respectively, and these values were significantly different from that measured on specimen (5.20 ± 0.89 cm, P < .05).

CONCLUSION

The extent of the VX2 malignant bone tumor can be estimated accurately by measurement of apparent diffusion coefficient value.

Accuracy of Various MRI Sequences in Determining the Tumour Margin in Musculoskeletal Tumours

Background

It is imperative that bone tumour margin and extent of tumour involvement are accurately assessed pre-operatively in order for the surgeon to attain a safe surgical margin. In this study, we comprehensively assessed each of the findings that influence surgical planning, on various MRI sequences and compared them with the gold standard – pathology.

Material/Methods

In this prospective study including 21 patients with extremity bone tumours, margins as seen on various MRI sequences (T1, T2, STIR, DWI, post-gadolinium T1 FS) were measured and biopsies were obtained from each of these sites during the surgical resection. The resected tumour specimen and individual biopsy samples were studied to assess the true tumour margin. Margins on each of the MRI sequences were then compared with the gold standard – pathology. In addition to the intramedullary tumour margin, we also assessed the extent of soft tissue component, neurovascular bundle involvement, epiphyseal and joint involvement, and the presence or absence of skip lesions.

Results

T1-weighted imaging was the best sequence to measure tumour margin without resulting in clinically significant underestimation or overestimation of the tumour extent (mean difference of 0.8 mm; 95% confidence interval between −0.9 mm to 2.5 mm; inter-class correlation coefficient of 0.998). STIR and T1 FS post-gadolinium imaging grossly overestimated tumour extent by an average of 16.7 mm and 16.8 mm, respectively (P values <0.05). Post-gadolinium imaging was better to assess joint involvement while T1 and STIR were the best to assess epiphyseal involvement.

Conclusions

T1-weighted imaging was the best sequence to assess longitudinal intramedullary tumour extent. We suggest that osteotomy plane 1.5 cm beyond the T1 tumour margin is safe and also limits unwarranted surgical bone loss. However, this needs to be prospectively proven with a larger sample size.

The use of plots in orthopaedic literature

Plots are an elegant and effective way to represent data. At their best they encourage the reader and promote comprehension. A graphical representation can give a far more intuitive feel to the pattern of results in the study than a list of numerical data, or the result of a statistical calculation. The temptation to exaggerate differences or relationships between variables by using broken axes, overlaid axes, or inconsistent scaling between plots should be avoided. A plot should be self-explanatory and not complicated. It should make good use of the available space. The axes should be scaled appropriately and labelled with an appropriate dimension. Plots are recognised statistical methods of presenting data and usually require specialised statistical software to create them. The statistical analysis and methods to generate the plots are as important as the methodology of the study itself. The software, including dates and version numbers, as well as statistical tests should be appropriately referenced. Following some of the guidance provided in this article will enhance a manuscript.