Askin Tumor - Presenting as a Case of Paraparesis: A Rare Clinical Entity. Case Report and Findings on ¹⁸F-Fluorodeoxyglucose-Positron Emission Tomography/Computed Tomography

Introduction

Askin-Rosai tumor (AT) is a rare primitive neuroectodermal tumor (PNET) developing from the soft tissues of the thoracopulmonary region, primarily occurs in adolescents and young adults aged between 10 and 30 years.[1] It belongs to the Ewing's sarcoma family of tumors sharing the same karyotype abnormality with translocation involving chromosomes 11 and 22.[2] The most common clinical presentation is a rapidly growing palpable mass overlying the chest wall.[3] Other common clinical presentations include pleural effusion, chest pain, prolonged fever, cough, dyspnea, and hemoptysis. AT is usually localized to the site of origin in the thoracic area at the time of presentation, although the tumor has a tendency to metastasize to the regional and distant sites.[3] The common sites of metastases include the lung, bone, bone marrow, and liver. Askin tumor presenting as compressive myelopathy is extremely rare. Herein, we describe a case of Askin tumor involving the spine with a rare presentation of paraparesis.

Case Report

A 24-year-old male with no comorbidities presented to the outpatient department with complaints of gradually progressive swelling in the upper back and weakness in bilateral lower limb for 3 months. At the time of presentation, the patient was paraplegic with 20%–40% sensory loss below D8 vertebral level bilaterally and with urinary and bladder incontinence. Neurological examination revealed power grading 5/5 in both upper limbs and 0/5 in bilateral lower limbs. Deep-tendon reflex was exaggerated in both the lower limbs. The patient was completely bed ridden, bladder catheterized with Grade 3 bed sores over the buttock region. Physical examination revealed 4 cm × 6 cm firm lesion in the back region. His magnetic resonance imaging of dorsal spin confirmed the presence of a well-defined multilobulated mass lesion epicentered in the right posterior chest wall extending from D5 to D10 vertebral level with invasion into the right thoracic cavity causing passive atelectasis of the underlying lung. The lesion was found to invade the right neural foramina at D6-D8 vertebral level with compression and displacement of spinal cord to the left side. It showing altered signal intensity appearing hyperintense on T2W1. Histopathological examination of tumor from the paraspinal mass showed features of malignant round cell tumor with nuclear immunoreactivity of NKX 2.2. The patient was started on prephase therapy. Post prephase therapy he was referred to the nuclear medicine department for a positron emission tomography/computed tomography (PET/CT) scan for work-up. PET/CT imaging was performed after intravenous injection of 10 mCi ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG). PET/CT revealed a metabolically active heterogeneously enhancing soft-tissue density mass lesion with areas of necrosis and calcifications in thoraco-pulmonary region involving the right posterior chest wall with destruction of right 6^th–8^th ribs and adjacent vertebra with infiltration into the spinal canal abutting and compressing the cord. Maximum calculated standardized uptake value (SUV_max) of the lesion was 4.36 [Figure 1]. There was moderate right pleural effusion. Few metabolically active subcentimetric right extra pleural deposits and metabolically active bilateral supraclavicular, right paratracheal, subcarinal and right retrocrural lymph nodes were also noted and deemed to be metastatic.

Close

Figure 1 Axial fused PET/CT (a) and CT (b) and coronal fused PET/CT (c) and CT (d) images in a 24-year-old boy with lower back pain revealed a FDG avid heterogeneously enhancing thoracopulomary mass lesion in the right paravertebral region with areas of necrosis and calcifications infiltrating into the right thoracic cavity and into the right side of spinal canal abutting and compressing the cord. The adjacent ribs and thoracic vertebrae show destruction due to tumor infiltration. PET/CT: Positron emission tomography/computed tomography, FDG: Fluorodeoxyglucose

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Discussion

PNETs can arise either form the central nervous system PNET or from periphery-PNET.[4] Peripheral PNETs most commonly involve the chest wall pleura, pericardium, and soft tissue. PNETs of the chest wall were originally reported by Askin et al. in 1979 in 20 children;[1] since then, PNETs that occur within the thoracopulmonary region are named as Askin's tumor. It is a rare malignant neoplasm, locally invasive in nature and prone to destroying bone (ribs and scapula) and spreading to lymph nodes, adrenals, and liver. Askin tumor infiltrating the spinal cord and presenting as a case of compressive myelopathy is rare. In a study of 104 patients of Askin tumor by Lashkar et al., asymptomatic swelling (43%) was the most common presenting symptom followed by pleural effusion. Lymphadenopathy was observed in 10.9% of cases and 25% of patient presented with distant metastases. None of the cases presented with compressive myelopathy.[5] In another case series of 11 patients by Ke Zhang et al., the most common clinical symptoms included fever, cough, chest pain, and suffocation.[6] In a review of the literature on peripheral PNET of the thoracic region, Anjankar et al. reported 19 such cases with epidural mass in adults, with a female: male ratio of 1:1.7 and the average age of presentation at 30 years.[7] Presenting symptoms were back pain in all patients, followed by weakness in limb (70%), sensory loss (35%) and the diagnostic delay was approximately 4.5 months. There are not many case reports describing Askin tumor ¹⁸F-FDG PET/CT results. Xia et al. evaluated 6 patients of Askin tumor with ¹⁸F-FDG PET and observed that the lesion SUV_max varied from 4.0 to 18.6.[8] However, Kara Gedik et al. reported a SUV_max of 4.3 in their case report of 73-year-old male with Askin tumor.[9] In our case, the age at presentation was 24 year, patient reported with signs and symptoms of compressive myelopathy which is a rare presentation in AT. ¹⁸F-FDG PET/CT helped in characterization of metabolic activity of the tumor and in the detection of distant metastases. The metabolic activity of the tumor in our case was low (SUV_ma × 4.6) in concordance with Gedik et al. Metastatic nodes were observed in supraclavicular, mediastinal, and retrocural region. Supraclavicular and retrocural metastatic nodes were also observed by Xia et al. in 2 of their 6 patients undergoing FDG-PET scan. Winer-Muram et al. reported mediastinal lymph node metastases in 2 out of 8 Askin tumors,[10] while Sabate et al. reported mediastinal lymph node metastases in 1 out of 8 Askin tumors.[11]

The prognosis of AT is very poor. Because of rarity of the neoplasm, there are no consensus guideline. The treatment of Askin tumour is multidisciplinary including surgery, radiotherapy and chemotherapy aimed to control local disease and distant metastases.

Conclusion

This case emphasizes the fact that although Askin's tumor with compressive myelopathy is rare, it should be considered as one etiologic possibility in a young adult presenting as a case of paraplegia.