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.
IMAGING
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 |