Diagnosis

Radiation-induced osteosarcoma with right common iliac vein tumor thrombus.

Discussion

Anteroposterior pelvic radiograph (Fig. 1) demonstrates an aggressive, slightly expansile lesion within the right ischium. Contrast-enhanced CT image (Fig. 2) demonstrates a lytic acetabular lesion with an adjacent extensive large soft tissue component. Given the clinical history of the patient and single site disease, a primary bone tumor is favored over an osseous metastasis.

Fig. 1
figure 1

Initial anteroposterior pelvis radiograph demonstrating an aggressive, expansile lesion in the right ischium (red arrows)

Full size image
Fig. 2
figure 2

Contrast-enhanced axial CT image of the pelvis at the level of hip joints in bone window demonstrating a lytic, aggressive acetabular lesion (red arrow) with a soft tissue component (blue arrows)

Full size image

Follow-up oblique post-contrast CT (Fig. 3) and axial CT (Fig. 4) images demonstrate an incidental partially calcified thrombus involving the distal inferior vena cava, extending into the right common iliac vein. Fat-suppressed MRI (Fig. 5) re-demonstrates thrombus within the right common iliac vein with similar signal characteristics to the sarcomatous lesion. The imaging findings are consistent with a rare case of venous tumor thrombus (VTT).

Fig. 3
figure 3

Contrast-enhanced coronal CT image through the upper pelvis in soft tissue window demonstrating an irregular, partially calcified thrombus within the distal inferior vena cava, extending into the right common iliac vein (red arrows)

Full size image
Fig. 4
figure 4

Contrast-enhanced axial CT image through the pelvis in soft tissue window re-demonstrating the partially calcified thrombus within the distal inferior vena cava (red arrow)

Full size image
Fig. 5
figure 5

Fat-suppressed MRI sequence of the pelvis demonstrating similar signal characteristics of the sarcomatous lesion to the inferior vena cava thrombus (red arrow)

Full size image

Histology examination (Fig. 6) following CT guided biopsy of the bony lesion confirmed high grade osteoblastic sarcoma likely secondary to radiotherapy. At the time of writing the patient has been offered a hind quarter amputation with resection of the tumor thrombus.

Fig. 6
figure 6

Histopathological photomicrographs (hematoxylin and eosin staining) demonstrating high grade sarcoma

Full size image

VTT is most commonly described in patients with liver cancer, renal carcinoma, adrenal tumors, and Wilms tumor [1]. Intravenous tumor development secondary to radiation-induced pelvic sarcoma is a rare and unusual complication. It is typically an incidental finding following the staging of the disease; however, patients may present with pain or discomfort secondary to intravascular tumor growth. Accurate diagnosis has a large impact on surgical management as almost all the reported VTT cases demonstrate extremely poor outcomes [2]. VTTs usually originate from venous branches near the tumor and extending proximally within the lumen.

The survival outcomes of pelvic sarcomas sharply declines when complicated by VTT (22.4 vs 38.2 months), and perioperative mortality tremendously increases when an unanticipated VTT is found during the intra-operative period [3]. The presence of VTT demonstrates that hematogenous malignant spread has occurred and may be considered as an absolute contraindication to curative surgery.

Diagnosing and differentiating bland thrombus from tumor thrombus can be performed using a variety of imaging modalities and remains a vital aspect of the preoperative staging process to assist in planning treatment strategies. Radiological characteristics of tumor thrombus include increased caliber of the vessel secondary to intra-luminal tumor, continuity with the mass, calcification, and vessel wall enhancement [3]. Increased metabolic activity within the venous lumen on 18-FDG-PET/CT has been demonstrated to have a high sensitivity and specificity (71.4% and 90% respectively) in identifying occult VTT with accurate localization of the involved vessels [4].

Management of VTT requires careful evaluation of the resectability of the thrombus. A variety of techniques such as inferior vena cava filter, thrombectomy with vessel preservation, and open VTT resection should be utilized on a case-by-case basis. Post-operative control of local and distant recurrence is unknown and therefore close follow-up is advised.