Ewing sarcoma of the rib : respiratory tract infection as initial symptoms in a 14-year-old boy . Functional medical imaging findings

Figure 1. Computed tomography scan of the chest shows an expansive mass occupying the left hemithorax extending from the abnormal rib. Tumor was located over posterior arch of the left ninth rib. DOI http://dx.doi.org/10.13070/rs.en.1.839 Date 2014-05-28 Cite as Research 2014;1:839 License CC-BY Ewing sarcoma of the rib: respiratory tract infection as initial symptoms in a 14-year-old boy. Functional medical imaging findings


INTRODUCTION
Ewing sarcoma or primitive neuroectodermal tumor (PNET) of bone is the second most common pediatric malignant bone tumor.The median age at diagnosis is 15 years and there is a male predilection of 1.5/1.PNET are high-grade tumors that usually metastasize to lungs, pleural spaces and bones.The prognosis of the patients changes significantly in the absence and presence of metastatic disease.Present algorithm workup includes: computed tomography (CT) scan of the chest to study skeletal metastasis, magnetic resonance imaging (MRI) for local tumor extent and Tc-99m whole-body scintigraphy to exclude skeletal metastasis.However, these techniques differ in performance in terms of sensitivity and specificity, but none of the modalities alone seem to be able to yield a reliable diagnostic outcome.FDG positron emission tomography (FDG PET) has the ability to image tumor glucose metabolism noninvasively.FDG uptake is regarded as a surrogate marker for the degree of tumor aggressiveness in many malignancies.Besides, FDG PET is an ideal method to assess tumor response.Presented is a case of Ewing sarcoma of the rib which illustrates the importance of recognizing exceptional features when interpreting FDG PET or scintigraphy to prevent the misinterpretation of metastases as perhaps other etiologies, such as infection.(SUV max 1.9), suggesting etiologies such as infection or inflammation.Increased FDG uptake in pelvis was seen numerous millimeter focus in the left sacroiliac bone (SUV max 2.9), corresponding to the same pathological foci described on bone scintigraphy.A little abdominal focus localized in large bowel (cecum) suggested a benign process.

CASE REPORT
Postchemotherapy 18-F-FDG PET (Fig. 3A) revealed a diffusing increased uptake in the bone marrow, without foci, as a result of reaction to postchemotherapy pancytopenia.The image showed a full disappearance of rib tumor focus and right lung focus.Findings indicate a favorable response to therapy.There was not hypermetabolic activity corresponding to other pathological foci.The sacroiliac bone was difficult to assess due to the diffusing increased uptake of FDG.Scintigraphy (Fig. 3B) did not show any bone alteration.Pelvic magnetic resonance imaging (MRI) (Fig. 4) suggesting bone necrosis in the left sacral alae.Restaging computed tomography scan (Fig. 5) obtained following chemotherapy and surgery showed a fibrotic scar in the posterior basal segment of the lung.The bronchiectasis in the right lung suggested an infective airways disease in resolution phase.

DISCUSSION
Ewing sarcoma is preferentially located in the long bones or in the pelvis, the ribs being the third most frequent site (making up 10-15% of all cases) [2].Ewing sarcoma is the most frequent chest wall tumor in children and adolescents [3].Chest pain in children and adolescents leads to consideration of a number of differential diagnoses: musculoskeletal trauma, pneumothorax, pleurisy, myocarditis, pericarditis, respiratory infections, pleurodynia and bone malignancies [4].
The description of the local extent of a bone tumor requires X-ray and CT/MRI of the involved bone.A chest CT scan is required to rule out lung or pleural metastases.The screening for bone metastases consists to include 99mTc bone scintigraphy.Many centres are now using FDG-PET scanning or totalbody MRI to look for occult metastases.While the role of FDG PET-CT in detecting recurrence is less clear, its role in staging Ewing sarcoma seems to be well established [5].Other authors state that MRI imaging with Gd enhancement, FDG PET and thallium scan maybe useful for assessment after treatment [6].
Recently, more accurate radiological diagnosis has become possible because of functional examinations such as FDG PET.This case suggests that the importance of recognizing exceptional features when interpreting FDG PET or scintigraphy to prevent the misinterpretation of metastases as perhaps other etiologies, such as infection [7].

AFigure 2 .Figure 3 .Figure 4 .
Figure 2. (A): Bone scintigraphy scan was requested to rule out multiple lesions.The images shows increased local tracer localization in the left ninth rib and it was discovered a new lesion in the left sacral alae.(B): Coronal PET shows an area of increased FDG uptake in the posterior arch of the left a maximum standard uptake value of 6.6.

Figure 5 .
Figure 5. Axial chest CT obtained following chemotherapy and surgery shows a fibrotic scar in the posterior basal segment of the lung.