MRI and CT of Low-Grade Fibromyxoid Sarcoma in Children: A Report From Children's Oncology Group Study ARST0332

Abstract

Objective: The purpose of this article is to determine the MRI and CT features of low-grade fibromyxoid sarcoma in children.

Materials and methods: We retrospectively analyzed images of 11 pediatric patients with low-grade fibromyxoid sarcoma from a phase 3 clinical trial of nonrhabdomyosarcoma soft-tissue sarcoma (Children's Oncology Group Protocol ARST0332). MRI and CT were performed in 10 and four patients, respectively. Location, size, margin, and composition on imaging were correlated with pathologic findings.

Results: Tumors were located in the extremities in nine patients, and one tumor each was located in the tongue and lung. Tumors were deep in seven patients and superficial in four patients. All tumors were well defined, solitary, and nonmetastatic at presentation. Tumors were complex solid-cystic in eight patients and completely solid in three patients. On T1-weighted images, all tumors had at least some areas hypointense to muscles, and six had a split-fat sign. On STIR or T2-weighted images, eight tumors had areas hypointense to adjacent muscle, and eight tumors had fluid signal intensity. On contrast-enhanced MRI studies, eight tumors had thick enhancing internal septations, and three had peripheral nodular gyriform enhancement. When we correlated imaging to pathologic findings, areas with hypointense signal intensity on both T1- and T2-weighted images were likely related to fibrous component; areas with fluid signal intensity on T2-weighted images were likely related to myxoid component. On CT, all four tumors were hypodense to muscle, and one tumor showed punctate calcific foci.

Conclusion: Low-grade fibromyxoid sarcoma is hypodense to muscle on CT. MRI may identify both fibrous and myxoid components of this rare pediatric soft-tissue sarcoma.

Keywords: ARST0332; CT; Children's Oncology Group; MRI; low-grade fibromyxoid sarcoma; pediatrics.

Figure 1. 12 year old boy with LGFMS arising in the lung

Axial CT image of the chest with lung window shows a hypodense (compared to muscles on mediastinal window) tumor in the anterior segment of left lower lobe.

Figure 2. 10 year old girl with left tongue mass

(A) Axial T1 weighted image of the neck shows a predominantly hypointense mass involving the tongue muscles on the left side (arrow). (B) Axial contrast enhanced T1 weighted fat saturation image shows heterogeneous peripheral nodular gyriform enhancement of the mass. (C) Axial contrast enhanced CT image of the face shows mild enhancement of the hypodense mass in the muscles of the tongue on the left side. Note the tiny calcific focus along the medial aspect of the mass (arrow).

Figure 3. 3 year old boy with a left shoulder tumor

Sagittal contrast enhanced T1 weighted fat saturation of the left shoulder reveals moderate peripheral nodular gyriform enhancement of the tumor with a non-enhancing central component, mostly from fibrosis (hypointense on T2W image, not shown). Notice that the mass is invading the scapula with extension anterior to the scapula (arrow).

Figure 4. 12 year old boy with a right elbow tumor

(A) Axial T1 weighted image of the right elbow shows a slightly hyperintense mass in the biceps muscle with hypointense areas (arrow) along the lateral aspect of the mass. (B) Axial T2 weighted fat saturation image reveals a solid predominantly T2 hyperintense mass in the biceps muscle with few internal hypointense areas (arrow). (C) Axial contrast enhanced T1 weighted fat saturation image shows moderate heterogeneous enhancement of the tumor with less enhancement of the T2 hypointense area shown in Fig. 4B, consistent with fibrosis.

Figure 5. 15 year old girl with a thigh tumor

(a) Coronal T1 weighted image of the right femur shows a predominantly hypointense solid tumor involving the right ilio-psoas muscle. Notice the “split fat” sign along the lateral aspect of the mass (arrow). (b) Coronal T2 weighted fat saturation image of the right femur demonstrates that the tumor is predominantly hypointense to the surrounding muscles. Notice that the tumor is abutting the right common femoral vessels. (c) Contrast-enhanced coronal T1 weighted fat saturation image of the right femur shows moderate heterogeneous peripheral nodular enhancement of the tumor. Note that areas that are hypointense on T1 and T2W sequences enhance less than other areas, consistent with fibrosis.

Figure 6. 12 year old boy with a right groin mass

(a) Axial T1 weighted image of the pelvis shows a hypointense mass in the subcutaneous plane of the right groin (arrow). (b) On an axial T2 weighted fat saturation image, the mass shows almost entirely fluid signal intensity. Notice the T2 hypointense nodular component along the posterior margin of the mass (arrow). (c) Axial contrast enhanced T1 weighted fat saturation image shows peripheral enhancement with a non-enhancing central component in this complex cystic mass. Notice the nodular enhancement along the posterior margin of the mass (arrow). Synovial sarcoma should be considered in the differential diagnosis of soft tissue tumors with a cystic appearance.

Figure 6. 12 year old boy with a right groin mass

(a) Axial T1 weighted image of the pelvis shows a hypointense mass in the subcutaneous plane of the right groin (arrow). (b) On an axial T2 weighted fat saturation image, the mass shows almost entirely fluid signal intensity. Notice the T2 hypointense nodular component along the posterior margin of the mass (arrow). (c) Axial contrast enhanced T1 weighted fat saturation image shows peripheral enhancement with a non-enhancing central component in this complex cystic mass. Notice the nodular enhancement along the posterior margin of the mass (arrow). Synovial sarcoma should be considered in the differential diagnosis of soft tissue tumors with a cystic appearance.

Figure 7. 10 year old boy with a left shoulder tumor

Coronal contrast enhanced CT scan image reveals a slightly hypodense mass in the left supraclavicular region with a thin peripheral rim that is isodense to the surrounding muscles (arrow). Histologic examination shows a solid mass without cystic or necrotic changes.