Keywords
adrenal - Ewing sarcoma - FDG PET-CT - IVC thrombus
Introduction
Ewing sarcoma (EWS) is a round cell tumor primarily affecting skeletal system, with
a higher incidence in children and young adults after osteogenic sarcoma among skeletal
malignancies. Although rare, primary extraosseous EWS has been reported involving
chest wall, paravertebral and retroperitoneal region, and even rarer occurrence of
organ involvement (lungs, gastrointestinal, prostate, others).[1]
[2] Primary adrenal EWS is unusual in pediatric population with very few cases reported
till date. We present such a case of primary adrenal EWS in a 7-year-old boy with
tumor thrombus involving renal vein and inferior vena cava (IVC) with pulmonary thromboembolism
detected on positron emission tomography-computed tomography (PET-CT). The case emphasizes
on considering EWS as a differential diagnosis in aggressive presentation of adrenal
mass lesions in pediatric population and role of 18F-fluorodeoxyglucose positron emission tomography-computed tomography (18F-FDG PET-CT) scan in assessing disease burden that can guide diagnosis and early
management.
Case Presentation
A 7-year-old boy, presenting with complains of paroxysmal seizure, tachycardia, hypertension,
and respiratory distress and a palpable abdominal mass in left hypochondrium, was
admitted at our institution. Magnetic resonance imaging (MRI) abdomen done at another
center suggested a large left suprarenal mass lesion raising possibility of neuroblastic
tumor. Laboratory investigation revealed normal plasma cortisol, plasma-free metanephrine
and normetanephrine, and urinary metanephrine levels. Patient was referred to our
department for 18F-FDG PET-CT scan to further characterize the lesion and evaluate the disease extent.
The scan taken after 1 hour of 4 mCi of 18F-FDG injection. PET-CT scan showed high-grade FDG avid large, lobulated, heterogeneously
enhancing left adrenal mass lesion (maximum standardized uptake value: 9.2) with hypodense
necrotic areas within and associated thrombus in left suprarenal vein, extending in
both renal veins, and IVC reaching upto right atrium, with heterogeneous components
within showing mild FDG uptake suggesting tumor thrombus. In addition, bilateral pulmonary
thromboembolism was detected ([Fig. 1A–F]). No lymphadenopathy or distant metastasis was seen. Based on the clinical and PET-CT
findings, possibility of adrenocortical tumor was considered over neuroblastoma. However,
CT-guided biopsy evaluation of left adrenal mass revealed EWS, immunohistochemical
(IHC) profile showing intense expression of CD99, with Ki-67 index of 35%. After multidisciplinary discussion, the patient was treated with
chemotherapy including vincristine, ifosfamide, doxorubicin, and etoposide, showing
good symptomatic response. Treatment response PET-CT scan was performed after three
cycles of chemotherapy that showed significant decrease in size and FDG uptake of
primary left adrenal neoplastic lesion, and decrease in extent of IVC thrombus with
resolution of thrombus in renal and suprarenal vein, and pulmonary thromboembolism
([Fig. 1G, H]). Patient is doing clinically well on chemotherapy.
Fig. 1 Baseline PET-CT MIP (A), fused PET-CT coronal (B), transaxial (E), CECT axial (F) images show FDG avid large, heterogeneously enhancing left adrenal mass with hypodense-necrotic
areas within, associated FDG avid tumor thrombus in left suprarenal vein, both renal
veins, IVC reaching upto right atrium (C). Bilateral pulmonary thromboembolism was detected (D). Post chemotherapy PET-CT (G), CECT (H) images show significant decrease in size and FDG uptake of left adrenal lesion and
IVC thrombus.
Discussion
EWS is the second most common skeletal malignancy affecting adolescents after osteogenic
sarcoma.[3] Extraskeletal EWS is less frequently encountered and involves soft tissue and rarely
even organ involvement. Primary involvement of adrenal gland in EWS being extremely
rare is not considered among the usual differential diagnosis of adrenal mass in children.[2] Rather, based on the age group and site of involvement in our case neuroblastoma
and possibly adrenocortical carcinoma were our major differentials. Detection is commonly
done on CT scan or MRI, whereas in our case adrenal mass was characterized on whole
body FDG PET-CECT scan. These modalities help in differentiating benign from neoplastic
adrenal lesion. Adrenal EWS lesions have been reported as mass lesion with heterogeneous
enhancement, areas of necrosis or internal foci of calcification and being locally
aggressive in nature may involving adjacent vessels.[4]
[5]
[6] Our case showed similar features of large lobulated heterogeneously enhancing adrenal
mass with central areas of necrosis with tumor thrombus extending into adjacent renal
vein and IVC. Since adrenal involvement formed major bulk of the lesion on PET-CT
scan, possibility of adrenal metastasis was ruled out. There are no reports yet on
detection of primary EWS on FDG PET, and our case shows that lesions demonstrate FDG
avidity considering their aggressive nature. Although there are no specific imaging
findings on PET-CT pertaining to primary adrenal EWS, FDG PET-CT scan can help in
staging by determining the disease burden and thus guiding management. Additionally
in our case due to whole body imaging, bilateral pulmonary thromboembolism was detected.
Histopathology is the gold standard to determine this rare diagnosis, and EWS pathological
features include round blue cell tumor positive for pancytokeratin, membranous CD99
on IHC, and reverse-transcription polymerase chain reaction positive for EWSR1-FL1
gene that are highly sensitive.[7]
[8] Biopsy performed in our patient showed similar IHC characteristics. Treatment strategy
includes surgery and chemotherapy both. Our patient received chemotherapy demonstrating
a good response on subsequent posttreatment PET-CT. So, we see another benefit of
FDG PET in assessment of treatment response in EWS. Our case thus highlights the rarity
of the diagnosis of primary adrenal EWS with locally aggressive features detected
on staging FDG PET-CT scan, and the importance of including EWS as one of the differential
diagnoses of adrenal masses. Also, we must note that since these lesions are FDG avid,
FDG PET-CT is a useful modality in assessing metastatic burden and treatment response,
both of which guide management decisions.
