DOI: https://doi.org/10.21203/rs.3.rs-1711351/v1
Positron emission tomography (PET) combined with a magnetic resonance (MR) scanner (PET/MR) with 18F-fluorodeoxyglucose (FDG) tracer is being used in quite a few nuclear medicine centers. The aim of this study is to illustrate two uncommon cases of primary inferior vena cava leiomyosarcoma which were formerly evaluated with anatomical images such as computed tomography and ultrasound. These techniques were inferior in the definition of the tumor and its characteristics. F-18 FDG PET/MR was essential and provided all the necessary information: its origin, local extension, anatomo-metabolic behavior, form of presentation, and distant metastasis in one single diagnostic technique .PET/MR accurately contributed to the diagnosis in a shortened period of time and therefore, in the prognosis of this disease with greater benefits.
This article was previously presented as an e-poster at the 34th Annual Congress of the European Association of Nuclear Medicine.
Inferior cava vein leiomyosarcomas (LMS) are an unusual entity, rising from smooth muscle cells with low growth rates. These features show the low acknowledgement of this pathology, mainly due to its infrequency. Our medical staff was motivated to perform more complex studies available in our region, in order to improve localization accuracy of the suspected neoplasm, proving a precise diagnosis of an uncommon disease, later confirmed by histological studies.
Positron emission tomography (PET) combined with a magnetic resonance (MR) scanner (PET/MR) imaging plays a pivotal role in the abdominal evaluation and characterization of retroperitoneal tumor lesion and extension to neighboring organs. The shortage of literature and case reports promoted a bibliography discussion and the presentation of the cases.
The first patient, a 50 years-old woman starts with prolonged abdominal pain and distension. An abdominal ultrasound is performed which shows an expansive hipoecoic, heterogeneous mass in the retroperitoneum. Consequently, a non contrast computed tomography (CT) was required to characterize the lesion. It exhibited a hipodense mass which displaced neighbored organs with no clear diagnosis.
A retroperitoneal neoplasm is suspected, specifically a sarcoma, thus since our center has a PET/MR, it was executed (Fig. 1). PET/MR shows a retroperitoneal hypermetabolic lobulated, nodular image that compresses vascular structures and depends on them. It also displaces other organs such as the right kidney and lower portion of the liver. It intensifies in late images (initial SUVmax: 6.2 -late: 9.5).
Our second patient is a 64 years-old male with a history of drug addiction, weight loss and abdominal pain. Firstly, a CT scan showed moderate left pleural effusion, with a voluminous expansive lesion of 123 mm in contact with the upper pole of the right kidney, and with compressive effects on the liver parenchyma. After a suitable evaluation in which renal or adrenal origin were considered, a PET/MR was necessary to distinguish the tumor properly and its extension (Fig. 2).
For these complex cases, PET/MR was paramount to previously identify the site of origin of the neoplasm, extension, metabolic grade and distant metastasis and subsequently provide a correct treatment.
Both patients were evaluated with PET / MR with F-18 Fluorodeoxyglucose (FDG), in a full-body PET 3D TOF acquisition scan in Hybrid Resonator, PET/MR General Electric SIGNA 3 Tesla. Pathological studies with immunostaining showed high-grade spindle cell sarcoma in both patients. Consequently, they both commence chemotherapy treatment. The former patient additionally underwent radiation treatment with positive outcomes with regular follow-up imaging to monitor for recurrences. Sadly, the second patient died with no further image evaluation.
Inferior cava vein (IVC) leiomyosarcomas (LMS) are an unusual entity, rising from smooth muscle cells of the media, although it is the most frequent primary tumor from IVC. In general, LMS of the IVC accounts for 5% of all vascular LMS. Vascular LMS tumors represent about 1–2% of all LMS, which accounts for 10–20% of all sarcomas in correlation with the low proportion of cases described in the literature. Sarcoma represents 1% of all adult malignancies [1, 6]. Epidemiologically, they have been reported in women in a slightly higher proportion around 50 to 60 years-old [3]. Poor prognosis has been described among the brief literature found [6, 7] and a life expectancy of 5 years [5].
IVC leiomyosarcomas are retroperitoneal neoplasms with different growing patterns: intraluminal, extraluminal or mixed patterns. They could also be divided into an anatomical classification formerly described by Mingoli (Fig. 3). The first segment includes all venous structures under the renal veins, the second segment is described between the renal veins and the suprahepatic veins and the third one from the suprahepatic veins to above, into the right atrium [6]. LMS affects them in 35%, 45% and 20%, respectively, although the whole cava vein may be involved in around 10–17% of the cases described [2, 7, 12]. Considering our patients, we may report that patient number 1 and 2 are anatomically classified as segment 1 and 3, respectively.
The slow rate of sarcomas and the type of growth reflects the variety of symptoms and the late clinical presentation: from asymptomatic to vague abdominal pain, distension, palpable mass, obstructive syndrome, Budd Chiari syndrome, edema, hypertension and tumor thrombosis [8]. Despite its low metastatic potential, the most common sites are liver, lungs, lymph nodes and bone through vascular and lymphatic dissemination [3, 6, 7, 8]. Also, into the abdominal aorta, right kidney, adrenal and colon due to its nearness [3, 6, 7].
The differential diagnoses include the wide spectrum of retroperitoneal mass that could be divided in two groups. In the pediatric population, adrenal neuroblastoma and renal nephroblastoma are the top two in prevalence [6]. Cholangiocarcinoma, duodenal malignancies, angiosarcoma, neurogenic tumors, retroperitoneal fibrosis, retroperitoneal lymphoma and adrenal pheochromocytoma, renal cell carcinoma and pseudolipoma need to be contemplate among adults due their similar imaging characteristics such as enhancing solid mass, necrosis and hemorrhagic [6, 11].
It is admitted that histologic grade is the most important prognostic factor for adult soft tissue sarcomas. Consequently, the proficiency of PET/MR images to provide a metabolic grade is of utmost importance in the prognosis of these patients, as it may differentiate low grade from high grade sarcomas in an imaging scan with considerable anticipation to biopsy results. Sarcomas are a complex and non homogeneous group of neoplasms in their anatomical and histological presentations. According to an extended bibliography revision, the most commonly used are the French grading and the National Cancer Institute grading systems. Both of them have 3 grades and are based on mitotic activity, necrosis and tumor differentiation. The practical value of these scores relies on the type of treatment each tumor is sensible to. In this way, some of them are more chemotherapy or radiotherapy sensible, concluding that the histopathologic subtype is inextricably linked with the prognosis of the patient.
18F-FDG PET/MR owns the advantages of both separately methods combined in one single diagnostic approach. The three-dimensional capability of MR imaging allowed to delimit the vascular and neural structures with more accuracy, under considerably less exposure to radiation. MR also has higher soft-tissue resolution, with accurate visualization during portal fase [8]. Leiomyosarcomas are commonly hypovascular structures, however they express peripheral enhancement through this imaging modality [7]. LMS are typically lobulated, well-defined iso/hypointense masses on T1, mainly homogeneous due to necrotic areas [8, 12] and hyperintense on T2. Hemorrhage and calcification are less common findings [12]. Due to their high cellularity and particularly in high grade sarcomas, they have restrictions on DWI images [8]. MR sequences showed the proper anatomy, especially when there are voluminous masses, making clear that the inferior cava vein was the origin of the tumors in our cases presented (Figs. 1 and 2). Moreover, MR has the capacity to differentiate intraluminal mass from thrombus, a key feature that impacts the prognosis [7].
Imaging signs are pivotal for both radiologists and nuclear medicine physicians; the main two are described. First and foremost, the “positive embedded organ” sign depicts a retroperitoneal mass which appears to be embedded in the tumor, meaning that it arises from retroperitoneal structures [7, 9, and 10] (Fig. 4), negative embedded sign accounts the opposite. Secondly, the “peak sign” illustrates that the edge of an organ is deformed like a peak shape, so it is likely that the mass arises from that organ; rounded edges implicates a negative peak sign and that the tumor compresses the organ, not rising there [9] (Fig. 5).
PET imaging aims to identify metabolic activity as tumor uptake measured by the maximum tumor standard uptake value (SUVmax) is extremely valuable [5]. This imaging granding measure for sarcomas is based on their histological behavior [5]. Stephanie Punt et al analized 39 patients with IVC LMS in which PET scan was previously performed to any treatment. They identified a mean age of 53 years-old, medium SUV max of 9.3 and a medium tumor greatest dimension of 10 cm. Also, 48% of the histological analysis accounted for high grade sarcomas. All these parameters concur with our patients data. After comprehensive analysis they conclude that FDG-PET is a forward and premature indicator of the tumor´s degree as a higher SUVmax correlates with both higher tumor grade and greatest tumor dimension [5]. In conclusion, once again we reaffirm the position that the correlation between tumor grade and clinical impact relies on hystologic features (anticipated by PET images in a shorten period of time) as they may predict histologic behavior of the malignant process having a direct impact on patients' prognosis, and hence, treatment.
Moreover, as the whole body is examined and patients are usually diagnosed in late stages, this technique also allows, in a single scan, to identify the presence of distant metastases (Fig. 2). This factor contributes to patients´stadification and prognosis.
| TEACHING | POINTS |
|---|---|
| MR IMAGES | PET SCAN |
| -Peak sign and embedded organ sign | -High SUV max values |
| -Hypovascular tumors with peripheral enhancement | -Whole body scan |
| -Hemorrhagic and calcification are unlikely | -Time efficient |
| -High DWI restriction | -2 in 1 diagnosis study |
PET- MR is a noninvasive and considerably less radiation exposure study, not only used for characterizing leiomyosarcomas but also staging and predicting the patient's survival. Consequently, the use of PET/MR may contribute to individualized patient treatment planning.
This hybrid methodology combines the advantages of morfofuncional exams (MR) and the plus points of metabolic scan (PET), unified in a single exam, to provide a more certain diagnostic approach.
We consider that the positive outcomes of this review will motivate the use of PET/MR in vascular sarcomas neoplasm in more centers worldwide which would increase a further understanding of this rare neoplasm.
Ethics approval and consent to participate: informed consent to participate in the study was obtained from participants at the time of the studies.
Consent for publication: informed consent was obtained
Availability of data and material: The data supporting the conclusions of this article is included within the article
Competing interests : The authors declare that they have no competing interests
Funding : Not applicable
Authors' contributions: Brunela Ronchi: manuscript main editor and researcher. Gustavo Peña: editor. Carlos Sacchi: editor. All authors read and approved the final manuscript