May 2024

Thoracic Aortic Pleomorphic Sarcoma: A Rare Diagnostic Journey 

Dr D Taylor (ST2)
Dr S WP Ngu (Consultant)
Dr L Ling (Consultant)

Hull University Teaching Hospitals NHS Trust 

Introduction 

Undifferentiated pleomorphic sarcoma, also formerly known as malignant fibrous histiocytoma, is a high-grade aggressive soft tissue sarcoma with a high mortality rate. It is the most common soft tissue sarcoma encountered. Histopathological confirmation is essential for diagnosis. We present a case report of pleomorphic sarcoma of the thoracic aorta.  

Case Study  

A 50 year old male underwent an ultrasound assessment for right upper quadrant pain. This showed an incidental large right-sided pleural effusion. A contrast enhanced CT demonstrated a large, lobulated and heterogenous peri-aortic mass with apparent invasion of the descending thoracic aorta (Fig 1). Appearances were initially suggestive of a mycotic pseudoaneurysm with a contained leak and the patient was transferred to a tertiary centre whereby following discussion with the vascular team, he underwent an endovascular aortic repair. Repeated cultures and cytological analysis from the aspirated pleural effusion were inconclusive. 

An FDG 18F PET-CT study performed several weeks later showed intense peripheral FDG uptake of the peri-aortic mass, raising the suspicion of a mycotic aneurysm or necrotic collection (Fig 4). Additionally, there was progressive lytic destruction of the T11 vertebral body, thought to represent a focus of osteomyelitis. Malignancy was considered less likely at the time (Fig 5). 

The patient was treated with a prolonged oral course of antimicrobials and referred to Infectious Diseases. He then developed epigastric and back pain, and a repeat CT demonstrated worsening of the peri-aortic mass/ necrotic lesion/ collection, and associated erosion of the T10-T11 vertebral bodies. White cell count was normal and CRP mildly raised. The patient underwent an MRI spine for assessment of osteomyelitis and discitis. It demonstrated a heterogeneous T2 signal prevertebral mass directly infiltrating/eroding into the T10/T11 vertebral bodies, more in keeping with a malignant lesion (Fig 2).  

The patient was referred to the Cancer of Unknown Primary MDT and a CT guided biopsy was performed. Histology revealed a diagnosis of G3 pleomorphic sarcoma of the thoracic aorta. The patient was managed with palliative chemotherapy and has stable disease one year post initial presentation.  

Key Facts 

• Patients usually aged > 40 years old (peak 6th -7th decade) 

• Male predominance 

• Most common location is the thigh and leg, then upper extremities.  

• Most commonly presents as a large, painless, growing mass or spontaneous haematoma. Cytokine production may result in signs & symptoms of weight loss, fever, leucocytosis and eosinophilia, which can mimic infection1,2  

Learning Points  

• Importance of avoiding bias of an existing diagnosis 

• The lack of cultural growth and clinico-radiological response to empirical antibiotic therapy should have prompted consideration of an alternative diagnosis earlier. 

• Pleomorphic sarcoma is a rare diagnosis and the intra-thoracic location in this case is an unusual site of involvement. 

• Importance of multidisciplinary and multimodality approach to complex diagnostic dilemmas.   

References 

1. Rusthoven CG, Liu AK, Bui MM, et al. . Sarcomas of the aorta: a systematic review and pooled analysis of published reports. Ann Vasc Surg 2014;28:515–25. 10.1016/j.avsg.2013.07.012. 

2. Robles-Tenorio A, Solis-Ledesma G. Undifferentiated Pleomorphic Sarcoma. [Updated 2023 Apr 10]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK570612/ 

Figure 1: Initial CT with contrast reported possible mycotic pseudoaneurysm of the thoracic aorta given the multiple small irregular outpouchings of the intima. Associated large right pleural effusion.  

Figure 2: Post EVAR CT 

Figure 3: MRI spine demonstrating the prevertebral thoracic mass infiltrating / eroding the anterior T10 and T11 vertebral bodies associated with marked oedema. 

Figure 4: Figure 4: PET-CT showed intense peripheral metabolic activity within the peri-aortic lesion, suggestive of a localised necrotic mass/collection.  

Figure 5: Axial PET-CT showing focal avid uptake of the left T10 pedicle, site suspicious for osteomyelitis. 

Figure 6: Retrospective review of an outpatient CXR from 6 months earlier, indicating a large right posterior mediastinal mass involving the right lower thoracic aorta.