Myxomas and myxoid liposarcomas of the extremities: Our preliminary findings in conventional, perfusion, and diffusion magnetic resonance

Abstract

Background: The differentiation between myxomas and myxoid liposarcomas (MLPS) often is a serious challenge for the radiologists. Magnetic resonance imaging (MRI) is the most useful imaging technique in characterization of the soft tissue tumors (STT).

Purpose: To evaluate in a sample of myxomas and MLPS of the extremities, what morphological findings in conventional MRI allow us to differentiate these two types of myxoid tumors, in addition to analyzing the validity of the apparent diffusion coefficient (ADC) values of diffusion-weighted MRI (DW-MRI).

Material and methods: Magnetic resonance imaging studies in myxomas and MLPS of extremities searched in our PACS between 2015 and 2019. All studies had conventional MRI with T1, T2, and PD SPAIR sequences, while DW-MRI with ADC mapping and perfusion MRI with a T1 sequence repeated for 4 minutes after contrast injection were additional sequences only in some explorations. Two radiologists evaluated independently the MRI studies by examining the qualitative parameters. Apparent diffusion coefficient values were calculated using two methods-ADC global and ADC solid, and Receiver Operating Characteristic (ROC) curves were applied for analysis.

Results: The features were consistent with MLPS: size greater than 10 cm, heterogeneous signal on T1, and nodular enhancement, while the common findings for myxomas were a homogenously hypointense signal on T1 and diffuse peritumoral enhancement. The solid and global ADC values were higher in myxomas. We observed that the solid ADC value less than 2.06 x 10^-3mm² x s would support the diagnosis of MLPS against myxoma.

Conclusion: Overall, MRI with its different modalities improved the diagnostic accuracy when differentiating myxomas from MLPS of extremities.

Keywords: apparent diffusion coefficient; diffusion-weighted MRI; magnetic resonance imaging; myxoid liposarcoma; myxoma; soft tissue tumors.

Figure 1.

Diffusion sequences with four b-factors in a single axial plane to the left and ADC map to the right. ADC map with the calculation method of the numerical value of global ADC (A) and solid ADC (B). The solid ADC is obtained from the average value of two locations in the tumor with diffusion restriction in the b-factor = 1000.

Figure 2.

Perfusion MR exploration in a myxoma in vastus lateralis muscle. Up to the left (a–d), the same axial plane is shown four times: (a) prior to intravenous injection of contrast, show the tumor (arrow); (b) 30 s after arrival of bolus of gadopentetate dimeglumine, the enhancement of the femoral artery is appreciated (arrow); (c) at 2 min, and (d) 4.5 min that show the diffuse enhancement of tumor. Up to the right, with all dynamic series acquired, we draw one ROI in the femoral artery (ROI A) and two ROIs in the tumor (ROIs B and C). At the bottom, the time-intensity curve (TIC) is shown. The enhancement curve of the femoral artery is represented in pink, and the ROI in tumor is represented in white and blue. The curves are type II and with T0 or delay time of 20”.

Figure 3.

Dot plot of solid ADC values. Each dot corresponds to the ADC values obtained in our case series. The dashed line represents the threshold value obtained in the ROC analysis for solid ADC measurement system.

Figure 4.

Coronal T1 weighted (images at the top) and axial T2 weighted (images at the bottom). In the left, the lesion is homogenously hypointense on T1 and heterogeneously hyperintense on T2 (myxoma); in the right, the lesion is heterogeneously on T1 and T2, (MLPS).

Figure 5.

Intramuscular myxoma. T1-weighted sequence (A) reveals ovoid, well-defined, homogeneously hypointense lesion with fat cap. DP-SPAIR (B) and T2-weighted sequence (C) show hyperintense lesion with peritumoral edema. T1-weighted, before (D) and after (E) injection of contrast material presents the diffuse enhancement of the tumor and the peritumoral edema.

Figure 6.

Dot plots of solid ADC in different cases series. Each dot represents the mean and median ADC values of each series (legend) for myxomas, benign myxoid tumors (BM), MLPS, and malignant myxoid tumors (MM). Our results are represented by the squares. The number of cases of each series is right to each dot in parentheses. The dashed line represents the threshold value obtained in our study.