Imaging of primary bone tumors: determination of tumor extent by non-contrast sequences

Magnetic Resonance Imaging Biomarkers of Bone and Soft Tissue Tumors

Magnetic resonance imaging (MRI) is essential in the management of musculoskeletal (MSK) tumors. This review delves into the diverse MRI modalities, focusing on anatomical, functional, and metabolic sequences that provide essential biomarkers for tumor detection, characterization, disease extent determination, and assessment of treatment response. MRI's multimodal capabilities offer a range of biomarkers that enhance MSK tumor evaluation, aiding in better patient management.

Pediatric Osteosarcoma: Correlation of Imaging Findings with Histopathologic Features, Treatment, and Outcome

Osteosarcoma is the most common primary bone sarcoma in children. Imaging plays a pivotal role in diagnostic workup, surgical planning, and follow-up monitoring for possible disease relapse. Survival depends on multiple factors, including presence or absence of metastatic disease, chemotherapy response, and surgical margins. At diagnosis, radiography and anatomic MRI are used to characterize the primary site of disease, whereas chest CT and whole-body bone scintigraphy and/or PET are used to identify additional sites of disease. Treatment starts with neoadjuvant chemotherapy, followed by en bloc tumor resection and limb reconstruction, and finally, adjuvant chemotherapy. Preoperative planning requires precise tumor delineation, which traditionally has been based on high-spatial-resolution anatomic MRI to identify tumor margins (medullary and extraosseous), skip lesions, neurovascular involvement, and joint invasion. These findings direct the surgical approach and affect the options for reconstruction. For skeletally immature children, the risk of cumulative limb-length discrepancy and need for superior longevity of the reconstruction have led to the advent and preferential use of several pediatric-specific surgical techniques, including rotationplasty, joint preservation surgery, autograft or allograft reconstruction, and extendible endoprostheses. A better understanding of the clinically impactful imaging features can directly and positively influence patient care. Online supplemental material is available for this article. ^©RSNA, 2022.

Differentiation of microinfiltration and simple-edema areas in VX2 bone tumors by diffusion kurtosis imaging in animal experiments: a preliminary study

BACKGROUND

Dual-energy computed tomography, diffusion-weighted imaging (DWI), and dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) can be used to distinguish microinvasion areas of malignant bone tumors. However, reports of diffusion kurtosis imaging (DKI) to determine the extent of intramedullary infiltration are relatively rare.

PURPOSE

To assess the application value of MR-DKI in differentiating areas of microinfiltration and simple edema in rabbit bone VX2 tumor models.

MATERIAL AND METHODS

Conventional MRI and DKI were performed on 25 successfully constructed rabbit VX2 bone tumor models. We acquired a midline sagittal section of the tumor for hematoxylin and eosin staining. Using pathological findings as the gold standard and combining them with MRI data, strict point-to-point control was performed to delineate regions of interest (ROIs) in the microinfiltration and simple-edema areas of bone tumors for quantitative measurement of mean diffusivity (MD) and mean kurtosis (MK). MD and MK values between microinfiltration and simple-edema areas were compared using an independent sample t-test, and the diagnostic values were evaluated by receiver operating characteristic (ROC) curve analysis.

RESULTS

In comparison with the simple-edema area, the micro-infiltration area demonstrated significantly smaller MD values and larger MK values (P < 0.05), and MD showed a better area under the curve (AUC) than MK (AUC = 0.884 vs. AUC = 0.690) for distinguishing the microinfiltration area from the simple-edema area. The optimal cutoff MD value was 1108.5 mm²/s with a sensitivity of 84% and specificity of 84%.

CONCLUSION

DKI can distinguish the microinfiltration and simple-edema areas of malignant bone tumors in animal experiments.

Pathological fracture in paediatric bone tumours and tumour-like lesions: A predictor of benign lesions?

OBJECTIVE

To determine the incidence and causes of pathological fractures in paediatric bone tumours and tumour-like lesions, and to determine if they are predictive of benign lesions.

METHODS AND MATERIALS

Retrospective review of children with suspected bone tumours referred to a specialist musculoskeletal oncology service between September 2019 and August 2020. Data recorded included patient age and gender, lesion location, the presence of a pathological fracture on the initial plain radiograph, and the final diagnosis made either by image-guided biopsy/curettage or based on typical imaging features.

RESULTS

231 patients were included with 233 lesions (138 males and 93 females with mean age 10.5 years, range 3 months-18 years). Final diagnosis was based on histology in 85 (36.5%) cases and imaging in 148 (63.5%) cases, 52 (22.3%) lesions classed as non-neoplastic, 139 (59.7%) as benign and 42 (18%) as malignant. Pathological fractures were seen in 41 cases (17.6%) at presentation, involving the humerus in 19 (46.3%), the femur in 14 (34.1%), the tibia in 3 (7.3%), the fibula and radius in two each (4.9%) and the second toe proximal phalanx in 1 (2.4%) (p < 0.001). The commonest underlying lesions included simple bone cyst (n = 17; 41.5%) and non-ossifying fibroma (n = 10; 24.4%). Only 4 cases (9.75%) were malignant, one case each of osteosarcoma, Ewing sarcoma, leukaemia and BCOR undifferentiated round cell sarcoma. Pathological fracture occurred in 27.7% of non-malignant lesions and 9.5% of malignant lesions, this difference being statistically significant (p < 0.001).

CONCLUSION

Pathological fractures were seen in 17.6% of paediatric bone tumours, tumour-like lesions, being significantly associated with humeral location and non-malignant diagnosis.

ADVANCES IN KNOWLEDGE

Demonstrates the frequency, location and underlying diagnosis of pathological fractures in paediatric bone tumour and tumour-like lesions.

Comparison of T1-weighted turbo spin echo and out-of-phase T1-weighted gradient echo Dixon MRI for the assessment of intra-medullary length of appendicular bone tumours

OBJECTIVE

Intra-medullary tumour length is accurately assessed on T1-weighted turbo spin echo (T1W TSE) MRI which can be relatively time consuming, whilst the gradient echo Dixon (T1W GrE Dixon) technique is a rapid sequence (imaging time ~ 30 s). The aim of this study was to determine if the out-of-phase Dixon (OP T1W GrE Dixon) sequence can produce equivalent measurements of intra-medullary tumour length compared to the T1W TSE sequence.

MATERIALS AND METHOD

Tumour length was assessed in 90 patients undergoing MRI for staging of primary bone tumours with both T1W TSE and OP T1W GrE Dixon MRI sequences at 3 T (n = 42) and 1.5 T (n = 48). Tumour length was measured independently by different observers allowing assessment of inter-observer correlation, and the correlation between measurements on T1W TSE and OP T1W GrE Dixon sequences was also determined.

RESULTS

There were 53 males and 37 females (mean age 36.4 years; range 2-77 years). Inter-observer correlation for tumour length on both the T1W TSE and T1W OP GrE Dixon sequences was very good (ICC = 0.94-0.98), and measurement of tumour length comparing T1W TSE and T1W GrE Dixon was also very good (ICC = 0.91-0.99). In 4 cases, tumour length was significantly overestimated on T1W TSE images due to extensive reactive marrow oedema, but more accurately determined on the OP sequence when compared to resection specimens.

CONCLUSIONS

The OP T1W GrE Dixon sequence is comparable to T1W TSE for assessment of the intra-medullary length of appendicular bone tumours, and more accurate in the presence of extensive reactive marrow oedema.

Quantitative magnetic resonance imaging for determining bone marrow fat fraction at 1.5 T and 3.0 T: a technique to noninvasively assess cellularity and potential malignancy of the bone marrow

BACKGROUND

Pediatric bone marrow assessment by MRI is challenging and primarily experiential and qualitative, with a paucity of clinically useful quantitative imaging techniques.

OBJECTIVE

MRI fat fraction (MRI-FF) is a technique used to quantify the degree of fat in other organ systems. The purpose of this study was to assess whether MRI-FF accurately measures bone marrow composition.

MATERIALS AND METHODS

This two-part study included a validation phase, followed by an application phase. For the validation phase, the MRI-FF of piglet bones (6 long bones, 8 axial bones) was performed at 1.5 tesla (T) and 3.0 T, and correlated to the histological fat fraction (H-FF). We used Bland-Altman plots to compare MRI-FF at 1.5 tesla T and 3.0 T. For the application phase, five children with malignant marrow disease were recruited along with seven age- and gender-matched control subjects. The MRI-FF in the children was correlated to the H-FF. Boxplots were used to compare the MRI-FF of patients and control subjects.

RESULTS

For the validation animal study, the MRI-FF of piglet bones at both 1.5 T and 3.0 T demonstrated moderate positive correlation to H-FF (r=0.41 and 0.42, respectively). MRI-FF at 1.5 T and 3.0 T were in good agreement, on average 7.7% apart. For the application phase, we included 5 children (4 with leukemia, 1 rhabdomyosarcoma) with median age 7 years, range (3-10 years). All children had MRI-FF and H-FF below 10%. The MRI-FF in patients (3.8±1.2) was significantly lower than that of control subjects (46.1±12.3%) (P<0.01).

CONCLUSION

MRI-FF is a valid technique to assess bone marrow fat fraction at both 1.5 T and 3.0 T. The MRI-FF in children with malignant marrow processes is significantly lower than in control subjects with normal marrow.

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.

The sensitivity, specificity, and diagnostic accuracy of whole-bone MRI for identifying skip metastases in appendicular osteosarcoma and Ewing sarcoma

OBJECTIVE

Pre-operative whole-bone MRI is required to assess intra-osseous tumour extent and to identify skip metastases in cases of bone sarcoma. The current study aims to determine the sensitivity, specificity, and diagnostic accuracy of whole-bone MRI for the identification of skip metastases.

MATERIALS AND METHOD

Review of 162 patients with long bone osteosarcoma or Ewing sarcoma who had undergone whole-bone MRI to assess intra-osseous tumour length and identify skip metastases. Comparison was made with post-chemotherapy MRI to look for a change in the appearance of suspected skip metastases, and resection specimens were assessed for the presence of skip metastases. The presence of local osseous recurrence was determined at final follow-up.

RESULTS

There were 112 males and 50 females (mean age 18.8 years), with 119 osteosarcomas and 43 Ewing sarcomas. Skip metastases were diagnosed on whole-bone MRI in 23 cases (14.2%). In 2 cases, pre-operative needle biopsy diagnosed enchondromata, resulting in false positive diagnoses. Skip metastases were diagnosed in the resection specimens in 3 cases, and based on comparison with post-chemotherapy MRI in 12. There was no evidence of local osseous recurrence in 160 patients, while late recurrence occurred in 2 patients. Sensitivity was calculated as 88.2%, specificity as 97.6%, and diagnostic accuracy as 96.7%.

CONCLUSION

Whole-bone MRI has a high sensitivity, specificity, and diagnostic accuracy for the identification of skip metastases in osteosarcoma and Ewing sarcoma. The possibility of false positive skip lesions and late local osseous recurrence is also highlighted.

The Dixon technique for MRI of the bone marrow

Dixon sequences are established as a reliable MRI technique that can be used for problem-solving in the assessment of bone marrow lesions. Unlike other fat suppression methods, Dixon techniques rely on the difference in resonance frequency between fat and water and in a single acquisition, fat only, water only, in-phase and out-of-phase images are acquired. This gives Dixon techniques the unique ability to quantify the amount of fat within a bone lesion, allowing discrimination between marrow-infiltrating and non-marrow-infiltrating lesions such as focal nodular marrow hyperplasia. Dixon can be used with gradient echo and spin echo techniques, both two-dimensional and three-dimensional imaging. Another advantage is its rapid acquisition time, especially when using traditional two-point Dixon gradient echo sequences. Overall, Dixon is a robust fat suppression method that can also be used with intravenous contrast agents. After reviewing the available literature, we would like to advocate the implementation of additional Dixon sequences as a problem-solving tool during the assessment of bone marrow pathology.

[The importance of radiology in bone sarcoma diagnostics : Initial and advanced diagnostics]

BACKGROUND

Reliable diagnostic assessment of malignant bone lesions remains a challenge in all the medical disciplines involved. The high incidence of benign (mainly pediatric) bone lesions needs to be distinguished from the rare malignant counterparts. If clinical presentation and patient history are unable to exclude a malignant tumour, adequate imaging of the affected region is necessary.

OBJECTIVES

This article focuses on giving implementable advice in dealing with problems and questions arising in the diagnostic process of treating patients with suspected or confirmed bone sarcoma. Also, follow-up recommendations from a radiological point of view are presented.

METHODS

Review and discussion of relevant literature against personal experiences in the medical imaging of patients with bone sarcomas.

RESULTS

Interpretation of projection radiographic images usually succeeds in assessing a bone tumour's dignity by evaluating periosteal reaction, the formation of a tumour matrix and consideration of the Lodwick classification. A current adaptation of the classic Lodwick classification incorporates diagnostic possibilities of more recent imaging techniques (magnetic resonance imaging (MRI), positron emission tomography (PET)) and is presented in this article. Plain radiographs are superseded by MRI as the primary imaging performed when depicting bone lesions with increasing frequency. The role of MRI in terms of primary diagnostics, staging, planning of biopsy tracts and tumour resections, evaluation of treatment response and follow-up are discussed. All diagnostic imaging techniques, including whole-body imaging methods, relevant in the diagnosis and therapy of bone sarcomas are presented in the sequence in which they appear during treatment.

CONCLUSIONS

Radiological imaging and expertise are important pillars in diagnosis and treatment of bone sarcomas. A variety of complementing imaging techniques provide a treatment-relevant basis significant for all medical disciplines involved.

The current status of MRI in the pre-operative assessment of intramedullary conventional appendicular osteosarcoma

Osteosarcoma is the commonest primary malignant bone tumour in children and adolescents, the majority of cases being conventional intra-medullary high-grade tumours affecting the appendicular skeleton. Treatment is typically with a combination of neo-adjuvant chemotherapy, tumour resection with limb reconstruction and post-operative chemotherapy. The current article reviews the role of magnetic resonance imaging (MRI) in the pre-operative assessment of high-grade central conventional osteosarcoma.

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.

Chemical shift imaging with in-phase and opposed-phase sequences at 3 T: what is the optimal threshold, measurement method, and diagnostic accuracy for characterizing marrow signal abnormalities?

OBJECTIVE

To determine the threshold signal drop on 3-T chemical shift imaging (CSI), with in-phase (IP) and opposed-phase (OP) sequences, for accurately identifying bone marrow replacement with 100% sensitivity, and determine a clinically useful measurement method for deriving such a threshold.

MATERIALS AND METHODS

From a convenience series of 157 MRIs, 36 cases with histologically proven marrow-replacing lesions and 22 sites of red marrow (histologically proven (2) or with minimum 6-month stability) with 3-Tesla CSI were included. Two musculoskeletal radiologists performed two measurement methods (first: multiple algorithmic ROIs at the top, middle, and bottom of lesions (M-ROI); second: an ROI was drawn where there appeared to be the least opposed-phase signal reduction qualitatively/visually (Q-ROI)). Lesional and red marrow signal change (%,[(IP-OP)signal/IP signal]*100) was determined. Statistical analyses included Student's t test, Cohen's kappa, and receiver operator characteristic curve generation.

RESULTS

By M-ROI, lesion signal change was - 0.508% (confidence interval (CI) = - 5.537:4.521) and 1.348% (CI = - 3.541:6.311) for readers 1 and 2. By Q-ROI, lesion signal change was - 11.03% (CI = - 17.01:- 5.046) and - 5.657% (CI = - 12.36:1.048) for readers 1 and 2. For all M-ROI and Q-ROI measurement strategies, signal change between lesional tissue and red marrow was significantly different (p < 0.0001). QROI produced the best composite sensitivities and specificities with a maximized Youden index of 0.955-1. A threshold signal drop of 25% with Q-ROI produced at least 100%/86% sensitivity/specificity for both readers for identifying marrow replacement.

CONCLUSIONS

For 3-T CSI, a single visually targeted measurement using a 25% threshold is accurate for identifying marrow-replacing lesions.

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.