A Rare Case of Abdominal IVC Pleomorphic Leiomyosarcoma on 18-F FDG PET CT Scan

INTRODUCTION

Leiomyosarcoma of the inferior vena cava (IVC) is a rare malignant tumor, arising from the smooth muscle fibers of vascular media, accounting for 2%^[1] of all leiomyosarcomas, making it the most common primary IVC neoplasm. It presents in an insidious manner with nonspecific symptoms. Among the various histological subtypes, pleomorphic accounts for around 8.6%.^[2] Although leiomyosarcomas are usually indolent and associated with good prognosis, pleomorphic leiomyosarcoma (PLMS) has an aggressive malignant potential with poor prognosis. They are usually managed by means of en bloc resection with clear margins where possible. Ultrasound (USG) is the initial imaging modality, while computed tomography (CT) scan or magnetic resonance imaging (MRI) can help in lesion characterization and extent.^[3] Whole-body 18-F fluorodeoxyglucose positron emission tomography CT (18-F FDG PET CT) scan is beneficial not only in delineating the primary disease lesion and its extent but also metastatic disease detection, determining tumor metabolism and in certain cases also helps in guiding site of biopsy. We would like to report the rare case of primary IVC leiomyosarcoma-pleomorphic subtype invading duodenum and pancreas detected on 18-F FDG PET CT scan.

CASE REPORT

A 47-year-old-female, presented with complaints of continuous, nonradiating right-sided abdominal pain, and sudden onset pain and swelling in the right lower limb. USG abdomen showed an irregular heterogeneously hyperechoic solid mass abutting the inferior medial pole of the right kidney, IVC, head of pancreas, and duodenum raising a suspicion of neoplasm. 18-F FDG PET-CT scan was performed to further characterize the lesion, its extent, and to look for metastatic sites, which revealed a high grade FDG avid Maximum Standardized Uptake Value or SUV max 22.7 large lobulated centrally necrotic retroperitoneal soft-tissue mass lesion invading the infrarenal IVC which was not separately visualized at the level of lesion, and also involving adjacent uncinate process of pancreas. Lesion was also abutting D2-D3 segments of duodenum, anterior cortex of right kidney, and infrarenal abdominal aorta with indistinct fat planes [Fig 1]. These features raised the possibility of a primary neoplasm likely arising from the IVC. Furthermore, a non-FDG avid long segment partial occluding filling defect/thrombus was noted in the rest of IVC up to left common iliac vein and linear non-occlusive thrombus in right common and bilateral external iliac veins [Fig 2]. No metastatic disease sites were detected on 18-F FDGPET-CT scan.

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Fig 1:

Computed tomography (CT) (a) and positron emission tomography-CT (b) Axial image showing metabolically active centrally necrotic retroperitoneal mass abutting duodenum, anterior cortex of right kidney, and infrarenal abdominal aorta with indistinct fat planes

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Fig 2:

(a) Maximum intensity projection image showing abnormal increased uptake in the abdomen (blue arrow). (b) Coronal computed tomography (CT) image showing retroperitoneal mass with longsegment partial occluding filling defect/thrombus in the infrarenal inferior vena cava extending into the left common iliac vein (c) positron emission tomography CT coronal image showing increased uptake in the retroperitoneal mass

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USG Doppler of lower limbs further confirmed deep-vein thrombus (DVT) in infra renal IVC, bilateral common iliac vein, right external iliac vein and common femoral vein. Two dimensional echocardiogram (2D ECHO) was normal with an ejection fraction of 55%. The patient was started on low-molecular-weight heparin in view of DVT and a suprarenal IVC filter was placed. CT-guided biopsy was performed from the FDG avid areas in retroperitoneal mass using PET-CT scan images as a guide. Histopathology showed spindle cell sarcoma likely of fibroblastic/myofibroblastic line. She underwent exploratory laparotomy with IVC tumor resection, Whipple’s procedure, right nephrectomy, and partial right adrenalectomy. Surgical histopathology confirmed unifocal leiomyosarcoma of pleomorphic subtype in the retroperitoneum arising from IVC and invading the second part of duodenum and pancreas and adherent to the ureter via fibroinflammatory response. The surgical margins were clear with all lymph nodes negative for tumor (pT3N0). Tumor histology consisted of sheets of haphazardly arranged spindle to oval cells with atypical eccentrically placed smudged, hyperchromatic nuclei [Fig 3]. Immunohistochemistry showed positivity for SMA, EMA, with focal expression of AE1/AE3, vimentin and desmin. Ki67 proliferation index was 5%–6%. A separate IVC thrombus was also examined which was free of tumor. The patient was discharged with pigtail drain and IVC filter in situ (removed after 2 weeks’ postsurgery), with low-molecular-weight heparin continued. Further management with adjuvant chemotherapy is being considered.

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Fig 3:

Sheets of haphazardly arranged spindle to oval cells with atypical eccentrically placed smudged, hyperchromatic nuclei on histopathological examination (Hematoxylin and Eosin, 400x)

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DISCUSSION

Vessel derived LMS accounts for <2% of all cases and usually are seen to arise from the IVC, pulmonary vein, and femoral vein.^[2] It commonly metastasizes via the blood stream.

IVC leiomyosarcomas are mesenchymal retroperitoneal tumors, with a female preponderance of 74% and mean age of presentation being 52 years.^[4] Extraluminal extension is common and is seen in as high as 76% cases,^[4] commonly involving the kidney, adrenals, pancreas, and duodenum. Intraluminal extension is often associated with thrombus. Our patient also demonstrated a lower IVC LMS with extraluminal extension.

PLMSs are a rare subtype of leiomyosarcomas. They are composed of pleomorphic cells with or without abundant eosinophilic or fibrillary cytoplasm. IHC shows positivity for Muscle Specific Actin (MSA), desmin, h-caldesmon, and negative for CD117, S100, and HMB45. Positive staining for cytokeratin and EMA is also seen in less than half of the cases,^[5] and similar features were also seen in our patient histology. The rarity and the poor prognosis of a vessel derived PLMS makes appropriate treatment strategy and long-term prognosis difficult to comment upon. Curative intent surgery is an essential part of its management regardless of the grim prognosis.

USG, CT, and MRI are the imaging modalities used for lesion detection and characterization, while 18-F FDG PET-CT scan plays a useful role in primary tumor staging and metastatic disease assessment. In our patient, Ultrasound (USG) abdomen detected a retroperitoneal mass which was further assessed on an 18-F FDG PET

CT scan which characterized the retroperitoneal lesion to be involving/arising from IVC showing high tumor metabolism, and possible adjacent organ involvement, along with an additional segment of bland IVC thrombus and deep vein thrombosis (DVT). The absence of metastatic lesions was also confirmed. Studies have shown higher FDG activity or SUV max values correlate with higher tumor grade and aggressive histology,^[6] which also holds true for our patient. Thus, 18-F FDG PET-CT continues to provide a noninvasive way to characterize tumors and potentially predict patient survival. Further adjuvant management must be considered in view of its aggressive nature. Leiomyosarcoma shows moderate sensitivity toward chemotherapy. Newer approaches are under trials.

CONCLUSION

PLMS arising from IVC is a rare and aggressive tumor where 18-F FDG PET-CT scan can be a useful tool for the diagnosis, possible biopsy site identification, assess surgical resectability, and provide guidance for further management with respect to distant spread.