Incidental floating aortic mass as the initial presentation of primary aortic sarcoma

Summary

Primary aortic tumours are extremely rare, with fewer than 250 cases reported in the literature. We present the case of an octogenarian man with an incidental aortic mass detected on CT, initially misdiagnosed as a thrombus. Its atypical radiological features—large size in a high-flow area without an associated aneurysm—and persistence despite anticoagulation raised suspicion of an aortic tumour. However, imaging studies (positron emission tomography-CT and magnetic resonance angiography) were inconclusive. A definitive diagnosis of primary aortic sarcoma was made postmortem through histological examination of an embolic fragment obtained during emergency surgery for acute lower-limb arterial ischaemia, a fatal complication that ultimately led to the patient’s death. This case emphasises the importance of maintaining a high index of clinical suspicion for aortic tumours and highlights the critical need for further evidence and case reports to improve the multidisciplinary management of this exceptionally rare and highly fatal condition.

Background

Primary malignant aortic tumours are exceptionally rare, accounting for only 0.001% of all tumours.^{1 2} They may occur in patients with atherosclerotic disease or aneurysms and are often misdiagnosed as other vascular conditions, such as thrombi.^{3 4} Although uncommon, a tumorous aetiology should be considered when intravascular thrombi display atypical radiological features, particularly in high-flow areas or in the absence of underlying atherosclerotic disease.^{3 5} Diagnosis is frequently delayed, as these tumours are rarely suspected in clinical practice, and is often made postmortem during autopsy or postoperatively following urgent intervention for embolic complications.^{1 2} The prognosis is poor due to the tumour’s aggressive nature, the complexity of surgical intervention and the limited evidence supporting effective chemotherapy and radiotherapy regimens. Consequently, management is particularly challenging, with available data restricted to case reports and small retrospective series.^{1 2 6}

Case presentation

A man in his 80s, former smoker with a history of hypertension, diabetes mellitus, hyperlipidaemia and peripheral arterial disease in the lower limbs, was evaluated at the internal medicine clinic for a 3-month history of constitutional symptoms, including unintentional weight loss of approximately 8 kg in about 3 months and progressively worsening anorexia. He also reported abdominal discomfort and persistent constipation. Despite dietary and pharmacological interventions for constipation—including a high-fibre diet and the use of laxatives—there was no clinical improvement. At the time of the initial evaluation, blood tests were requested and revealed iron-deficiency anaemia, with a haemoglobin level of 120 g/L, representing a 20 g/L decrease from previous values. Due to the presence of constitutional symptoms and newly diagnosed iron-deficiency anaemia in an elderly man, faecal occult blood testing was performed, yielding two positive results out of three samples. Based on this clinical scenario, both an abdominopelvic CT scan and a colonoscopy were requested to investigate a potential colorectal malignancy. However, the colonoscopy had not yet been scheduled by the time the CT results became available.

Investigations

The CT scan revealed an irregular filling defect in the distal descending thoracic aorta, measuring 56×18×2 cm. Additionally, a 1.5 cm nodular filling defect was noted in the superior mesenteric artery (SMA), with distal recanalisation and a subcapsular splenic infarction measuring 35×16 mm (figure 1). Given the presence of extensive and significant aortic atherosclerotic disease, these findings were initially interpreted as atherosclerotic thrombi. Notably, there was no evidence of thoracic or abdominal aortic aneurysms, signs of intestinal ischaemia, gastrointestinal lesions suggestive of malignancy, abdominal lymphadenopathy or hepatic space-occupying lesions.

Figure 1. Initial CT scan with intravenous iodinated contrast. Sagittal (a) and axial CT slice images (b, c) show an incidental filling defect in the distal descending thoracic aorta, measuring 56×18 × 2 cm (solid arrow). A 1.5 cm nodular filling defect is observed in the superior mesenteric artery, with distal recanalisation (dashed arrow). Given the presence of extensive aortic arteriosclerotic disease, these findings were initially misinterpreted as arteriosclerotic floating thrombi.

Due to these findings, a radiological alert was activated, and the patient was admitted to the internal medicine department for further evaluation and clinical monitoring. On re-evaluation, the patient reported a 1-week history of postprandial abdominal pain localised to the left flank, suggestive of mesenteric angina. He also described an unintentional weight loss of approximately 8 kg over the past 3 months, as previously documented during the initial outpatient assessment. Physical examination revealed tenderness on palpation in the affected area, without signs of peritonitis. Laboratory results showed haemoglobin at 120 g/dL (normal range: 105–130 g/L), leucocytes at 11 × 10⁹/L with 70% polymorphonuclear cells (normal range: 4–10 × 10⁹/L), C-reactive protein (CRP) at 4 mg/dL (normal range: 0.0–0.5 mg/dL) and lactate at 1 mmol/L (normal range: <1.5 mmol/L). The outpatient colonoscopy was postponed due to the high procedural risk associated with the aortic lesion and the low clinical suspicion of colorectal malignancy, as the abdominal CT showed no gastrointestinal lesions or abdominopelvic lymphadenopathy.

The case was discussed with the on-call vascular surgery team, and a floating thrombus—presumed secondary to plaque rupture—was considered the most likely diagnosis. Anticoagulation with low molecular weight heparin at a dose of 1 mg/kg twice daily, along with high-potency statins and radiological monitoring, was recommended. A follow-up CT angiography performed 10 days later showed no changes from the previous imaging.

Differential diagnosis

At this point, the differential diagnosis was broadened due to the atypical radiological features for an aortic thrombus and the patient’s clinical course. A multidisciplinary team meeting, including specialists in vascular surgery and internal medicine, was convened to review and discuss the case. The polylobulated morphology, its considerable size (>5 cm) within a high-flow region (descending thoracic aorta), absence of an associated aneurysm (which could explain local blood stasis) and lack of response to anticoagulation raised suspicion of a potential aortic tumour (figure 1). A biopsy was not performed due to the lesion’s location and the high risk of embolisation associated with invasive manipulation. Consequently, non-invasive imaging tests were conducted to evaluate a potential tumorous aetiology.

A positron emission tomography (PET) with 18-fluorine-fluorodeoxyglucose (18F-FDG) combined with CT (PET-CT) was initially performed (figure 2). The PET-CT revealed a polylobulated, septated, hypodense lesion within the descending thoracic aorta and at the origin of the SMA, with no significant radiotracer uptake and low suspicion for high-grade malignancy.

Figure 2. Positron emission tomography with 18-fluorine-fluorodeoxyglucose combined with CT. A polylobulated/septated hypodense lesion is observed within the aortic lumen at the level of the descending thoracic aorta (a) (solid white arrow) and at the origin of the superior mesenteric artery (b) (dashed white arrow), without significant radiotracer uptake and low suspicion of high-grade malignancy (c).

Magnetic resonance angiography (MRA) of the aorta with gadolinium was also performed. The MRA revealed an endoluminal lesion occupying the thoracoabdominal aorta (57 mm) and another in the SMA (figure 3). On dynamic contrast-enhanced sequences (DCE-MRA), mild enhancement was observed during the late phase of the lesion’s enhancement curve in comparison with the aortic lumen (figure 3d), a feature that could be suggestive of a neoplastic process. However, due to the minimal degree of enhancement, the lesion was ultimately reported as non-enhancing and considered more consistent with thrombus.

Figure 3. Magnetic resonance angiography of the aorta with gadolinium. Axial MRI image in T1 sequence with fat suppression, arterial phase (a, b). 3D reconstruction (c). Two non-enhancing filling defects are observed in the thoracoabdominal aorta (57 mm) (a) (solid arrows) and in the superior mesenteric artery (b) (dashed arrows). In dynamic contrast-enhanced sequences, slight enhancement is visible in the second half of the lesion’s curve (solid arrow) (orange curve) compared with the aortic lumen (blue curve) (d).

Additionally, a comprehensive laboratory work-up was conducted to investigate non-tumorous aetiologies. All tests showed negative results, including antinuclear antibodies, rheumatoid factor, serum complement levels (C3 and C4), antiphospholipid antibody profile, non-treponemal tests (Rapid Plasma Reagin (RPR) and Venereal Disease Research Laboratory (VDRL)) (and serum IgG4 levels. The absence of systemic symptoms suggestive of autoimmune disease (eg, arthritis, uveitis, cutaneous rash) or features of IgG4-related disease (eg, retroperitoneal fibrosis on CT or glandular involvement), combined with no signs of infection (no fever or elevation of acute-phase reactants), no history of high-risk sexual exposure and entirely negative laboratory results, made an autoimmune or infectious aetiology highly unlikely. A transthoracic echocardiogram was also performed, which demonstrated preserved biventricular function and no evidence of intracardiac thrombus, thereby excluding a cardiac source of embolism.

Treatment

Alongside the aetiological work-up, a new multidisciplinary team meeting was held with specialists in internal medicine, vascular surgery and interventional radiology to define the optimal treatment plan.

The diagnosis of an aortic tumour remained a key differential diagnosis based on the initial CT findings and the clinical judgement and experience of the multidisciplinary team, despite the inconclusive results from the functional imaging studies (PET-CT and MRA). Although there was a high index of suspicion for a vascular neoplasm, the possibility of an adherent thrombus overlying an underlying vascular lesion could not be definitively excluded; therefore, the final management plan included anticoagulation therapy and elective aortic endoprosthesis placement to mitigate the risk of embolic events.

During hospitalisation, the patient experienced resolution of abdominal pain without any other associated symptoms. Anticoagulation therapy was administered with low molecular weight heparin at a dose of 1 mg/kg two times per day under nursing supervision. He was subsequently discharged on oral anticoagulation with rivaroxaban 20 mg/day, with elective readmission planned for the following week for aortic endoprosthesis placement.

Outcome and follow-up

The patient returned to the emergency department 6 days later with worsening pain in the left side of the abdomen. He reported strict adherence to oral anticoagulation therapy since discharge. A repeat CT angiography (figure 4) revealed a slight increase in the size of the filling defect in the distal thoracic aorta, now measuring 6.0 cm (previously 5.6 cm) with polylobulated contours and septa. The known filling defect in the SMA remained unchanged; however, reduced perfusion was observed in the first jejunal branches, along with distended intestinal loops with contrast enhancement, raising concern for intestinal ischaemia.

Figure 4. Follow-up CT scan with intravenous iodinated contrast. Note the slight increase in the size of the filling defect in the distal thoracic aorta (from 5.6 to 6.0 cm), with polylobulated contours and septa (solid arrow). A similar filling defect is observed in the superior mesenteric artery (dashed arrow), with decreased flow in the first jejunal branches and distended intestinal loops, suggestive of intestinal ischaemic changes (dotted arrow).

The patient was subsequently admitted to the vascular surgery department, where an elective open mesenteric thrombectomy was performed within 24 hours, alongside an intravenous infusion of unfractionated heparin titrated according to the activated partial thromboplastin time ratio.

In the immediate postoperative period, the patient developed acute arterial ischaemia in both lower limbs, requiring urgent bilateral transpopliteal thrombectomy. Embolic material, described as whitish and gelatinous, was retrieved and sent for histopathological analysis. The patient’s condition deteriorated rapidly thereafter, with persistent haemodynamic instability despite high-dose vasoactive support, oliguria and absence of pedal and popliteal pulses, all occurring within the context of multiorgan failure due to massive embolic release. The patient died 12 hours after the procedure, 33 days following initiation of the diagnostic process

Histopathological examination of the embolic material revealed arterial wall tissue with marked cellularity, areas of necrosis, frequent mitotic figures and rhabdomyoblastic differentiation within a myxoid stroma, features consistent with the diagnosis of aortic intimal sarcoma (figure 5).

Figure 5. Histological findings. The arterial wall exhibits high cellularity and necrosis, with mitotic nuclei and rhabdomyoblastic cells (solid arrow) within a myxoid matrix (H&E staining—a, b). Immunohistochemical analysis revealed a high-grade tumour (immunohistochemical staining—Ki-67 Proliferative Index—c). These findings are consistent with aortic intimal sarcoma.

Discussion

We present the case of a man in his 80s with an incidental finding of an aortic mass on a thoraco-abdominopelvic CT scan, ultimately diagnosed postmortem as an intimal aortic sarcoma. This case highlights the need for early clinical suspicion of this rare condition and continued case reporting to improve recognition and management of large-vessel endovascular tumours.

Primary malignant aortic tumours are extremely rare, comprising only 0.001% of all tumours.² Metastatic involvement of the aorta, typically from cancers such as lung or head and neck, is far more common, whereas primary aortic tumours are exceptionally unusual.^{1 2} The first case was described by W. Brodowsky in 1873, and since then, less than 250 cases have been reported.² For example, Rusthoven et al conducted a systematic review and pooled analysis of 165 cases of aortic sarcomas from 1951 to 2012.⁷ Similarly, a recent study by Vacirca et al identified only 218 cases of malignant aortic tumours reported in the literature from 1873 to 2017.² This rarity is further supported by the 2022 ACC/AHA Guideline for the Diagnosis and Management of Aortic Disease by the American Heart Association and the American College of Cardiology, which underscores the exceptional infrequency of primary malignant aortic tumours, the majority of which are sarcomas.¹

Primary malignant aortic tumours arise from mesenchymal cells and can be classified according to their origin as follows: angiosarcomas and intimal sarcomas (which develop from the endothelial cells and myofibroblasts of the tunica intima); leiomyosarcomas (originating from the smooth muscle cells of the tunica media) and fibrosarcomas/malignant fibrous histiocytomas (arising from fibroblasts and histiocytes of the tunica adventitia).^{8 9} The most common types are angiosarcomas (37%) and intimal sarcomas (30%).² The descending thoracic aorta is the most frequent location (34%), followed by the abdominal aorta (27%) and the aortic arch (11%).^{2 8}

Clinical manifestations are variable and often non-specific. Embolic events are the most frequent initial presentation, reported in approximately 50–85% of cases at diagnosis.^{2 7} These may manifest as intermittent claudication (25%), intestinal angina (28%) or abdominal pain (32%).² Constitutional symptoms (29%) such as weight loss or fatigue are also common.² Metastatic spread may occur—most frequently to bone, followed by the kidneys, liver and skin. Other reported presentations include low back pain (22%) or renal hypertension (18%).^{2 8 10} The typical clinical risk profile corresponds to a male smoker in his sixth decade of life with cardiovascular risk factors, sometimes accompanied by additional factors such as prior aortic surgeries, trauma or inflammatory aneurysms.² The patient in our case fitted this profile, presenting primarily with constitutional symptoms and postprandial abdominal pain.

Due to the non-specific clinical presentation, diagnosis requires imaging studies and a high index of suspicion, as confusion with thrombi or aortitis is common.^{3 4} Aortic CT angiography is usually the first test performed to characterise the lesion and is sometimes diagnosed incidentally during an examination requested for other reasons, as in our case. Suspicion of a tumour should be raised by atypical radiological findings, such as its presence in an aorta without atherosclerotic or aneurysmal disease, occurrence in high-flow areas, lobulated shape with pedicular anchoring, size greater than 5 cm, heterogeneous appearance and concurrent thrombosis.^{1 3 5} It is important to note that in some cases, no enhancement is observed with intravenous contrast on CT angiography, increasing the likelihood of misdiagnosis as a thrombus.^{3 5} This is particularly relevant for intimal tumours, which often present as floating intraluminal masses with narrow pedicles and minimal peripheral vascularisation, as seen in our case.

MRA with gadolinium can help differentiate a tumour from the aortic wall and atheromatous thrombus by demonstrating tumorous enhancement and identifying peri-aortic extension.³ Lesion enhancement and positive magnetic resonance perfusion, characterised by a gradual and delayed perfusion pattern compared with the blood pool, are key features for distinguishing primary aortic sarcomas from thromboembolic disease.¹¹ In DCE-MRA sequences, thrombi typically show a monophasic contrast curve, whereas tumours exhibit a gradual perfusion followed by a washout phase.^{11 12} Nevertheless, tumorous enhancement is not always observed, as primary aortic sarcomas without enhancement on CT or MRA—mimicking thrombi—have been reported.^{4 11} In our case, the DCE-MRA was initially interpreted as negative. Retrospective review, however, revealed subtle enhancement in the latter portion of the lesion’s curve, which had been overlooked and ultimately supports the diagnosis of an aortic tumour (figure 3d)

PET-CT with 18F-FDG is perhaps the most reliable method for distinguishing aortic tumours from thrombi, as aortic sarcomas exhibit significant metabolic uptake in up to 90% of cases.^{3 11} Since many aortic tumours demonstrate little or no discernible contrast enhancement on CT or MRA, PET-CT remains the most dependable tool for identifying malignancy through increased metabolic activity.¹¹ Nevertheless, FDG-negative cases have been reported, especially in association with tumour embolisms.^{11 13} In our case, no uptake was observed on PET-CT. This may be due to the tumour’s small pedicle attachment to the aortic wall, with minimal local vascularisation and an abundant myxoid matrix, which could reduce cellular FDG uptake. This highlights the importance of maintaining a high index of suspicion, as the absence of radiotracer uptake on functional imaging does not necessarily exclude malignancy.¹³

In our case, the lesion was initially interpreted as a thrombus, given its greater prevalence and the clinical context of a patient with cardiovascular risk factors and suspected atheromatous plaque rupture. However, subsequent multidisciplinary review involving vascular surgery and internal medicine specialists identified atypical features of the lesion, including its considerable size and location within a high-flow area of the aorta, which were more suggestive of a neoplastic process than a simple thrombus. Biopsy was not considered due to the elevated risk of distal embolisation; therefore, functional imaging with MRA and PET-CT was undertaken, on the basis that absence of contrast uptake would support a thrombotic origin, whereas enhancement would favour malignancy. Both studies showed no significant contrast uptake and were interpreted as consistent with thrombi. Nonetheless, suspicion of an underlying tumour remained high among the multidisciplinary team owing to the lesion’s atypical morphology and prior experience with a similar case.¹⁴ This led to a re-evaluation of the imaging in collaboration with the radiology department. On DCE-MRA sequences, subtle enhancement was noted in the latter part of the lesion’s enhancement curve compared with the aortic lumen, a finding suggestive of aortic malignancy (figure 3d).

In light of these considerations, histological examination remains the gold standard for establishing a definitive diagnosis.^{1 2} The rate of antemortem diagnosis is approximately 74%.¹³ Intra-arterial biopsy is generally discouraged due to the risk of embolism.^{2 13} The average time to diagnosis is 11.5±5.3 weeks.² It is not uncommon for aortic tumours to be incidentally diagnosed from surgical specimens of presumed thrombi, excised for other indications,^{1 3} and often described macroscopically as whitish and gelatinous. Based on the immunohistochemical profile, intimal angiosarcomas may express endothelial-specific antigens such as CD31, WT-1 and FLI-1.¹³ Mesenchymal markers like desmin and actin are positive in myofibroblastic sarcomas, while some sarcomas of undifferentiated stromal cell origin may only express vimentin.^{13 15} In this case, microscopic examination of the gelatinous tissue showed high-grade spindle cell proliferation and a positive Ki-67 index, confirming the diagnosis of primary intimal sarcoma.

Treating aortic tumours requires a multidisciplinary approach.^{1 2} According to the 2022 ACC/AHA Guideline for the Diagnosis and Management of Aortic Disease by the American Heart Association and the American College of Cardiology, optimal treatment involves surgical resection with aortic reconstruction followed by adjuvant chemo-radiotherapy.¹ Alternatives include endarterectomy or palliative endoprosthesis placement to reduce embolic risk, although recurrence within the prosthetic material has been reported.^{15 16}

The overall prognosis is poor. Postoperative mortality is high (45–60%) with a median survival of 8 months after diagnosis (1-year survival: 26%; 5-year survival: 35%).^{2 8} The most common cause of death is disseminated metastatic disease,⁸ as was the case in our patient. Poor prognostic factors include metastatic disease or embolisation at the time of diagnosis, certain histological subtypes like fibrosarcoma, clinical features such as hypertension, fever, back pain or asthenia and the absence of treatment.^{2 7} In contrast, the aortic location itself does not appear to influence prognosis.² Combined surgical and medical therapy has shown the greatest impact on median survival (12 (8–24) months), compared with surgery alone (7 (2–16) months) and no treatment (2 (0.5–15) months).^{1 2 7}

In our case, although an aortic tumour was not the initial working diagnosis, clinical suspicion progressively increased throughout the patient’s management and ultimately guided therapeutic decision-making. Surgical resection with aortic reconstruction was ruled out given the patient’s asymptomatic status, advanced age and the significant operative risk associated with descending thoracic aorta replacement. As a result, a palliative approach was adopted, assuming a presumptive diagnosis of aortic sarcoma, in order to minimise the risk of distal embolic dissemination. Anticoagulation was continued based on the possibility of a thrombus superimposed on the lesion, in the context of a prothrombotic state. Unfortunately, before any further intervention could be performed, the patient died from multiorgan failure secondary to a massive distal embolism. The final diagnosis of an aortic intimal sarcoma was therefore established postmortem.

This outcome underscores the educational value of the case and the importance of retrospective reflection in understanding the diagnostic complexity and therapeutic limitations associated with aortic tumours. A high index of clinical suspicion and a multidisciplinary medical and surgical approach are essential for early recognition and management, although the overall prognosis remains poor.

Learning points.

• Aortic tumours are extremely rare and may occur in patients with atherosclerotic disease or aneurysms, often mistaken for thrombi or incidentally identified on radiological exams.

• Although uncommon, tumorous aetiology should be considered when intravascular thrombi display atypical radiological characteristics, particularly in high-flow areas or in the absence of atherosclerotic or aneurysmal disease or when recurrent thrombosis remains unexplained.

• The absence of specific imaging findings underscores the importance of maintaining a high index of clinical suspicion.

• The prognosis is poor given the high surgical complexity and the risk of embolic events, making the involvement of a multidisciplinary medical and surgical team crucial.

• Reporting cases of aortic tumours remains essential, as it contributes to collective clinical learning and supports the standardisation of diagnostic and therapeutic approaches.