Rare tumours known as primary retroperitoneal neoplasms begin in the retroperitoneum but do not spread to the main retroperitoneal organs. They make for 0.16 percent of all cancers.¹ The diagnostic difficulties in assessing a retroperitoneal mass are precise localisation, estimating the degree of involvement, and characterising a particular pathologic type. Primary retroperitoneal diseases may have vague symptoms and are challenging to physically examine.^2,3

The three most common imaging modalities to assess abdominal masses are ultrasound (USG), computed tomography (MDCT), and magnetic resonance imaging (MRI).⁴ The preferred imaging technique for characterising retroperitoneal masses is multi-detector computed tomography (MDCT).⁵ It is employed in situations where USG findings are insufficient or to diagnose lesions that the USG was unable to image because of intestinal gas and body habit.⁶ In comparison to other imaging techniques, MDCT demonstrated superior performance in assessing vascular mobility, which is beneficial in forecasting the tumor's viability.⁷

Lesions that are not detected by USG and MDCT are diagnosed using MRI. MRI enables greater spatial and contrast resolution in the delineation of anatomical structures, as well as characterization of pathological lesions, and provides an excellent portrayal of retroperitoneal anatomy. MRI can be considered a fantastic tool for assessing retroperitoneal anomalies.⁸ In this geographic area, only a few studies have been done on the examination of retroperitoneal masses using MDCT and MRI. Present study was aimed to correlate the radiological results with those of histological or fine needle aspiration cytology (FNAC).

Present study was Hospital based Cross-Sectional Study, conducted in department of Radiodiagnosis, at Karnataka Institute of Medical Sciences, Hubballi, India. Study duration was of 18 months (January 2021 to June 2022). Study was approved by institutional ethical committee.

Inclusion criteria

• Clinically suspected patients presenting with symptoms of retroperitoneal masses OR Patients with incidentally detected retroperitoneal masses by routine ultrasonography of

Exclusion criteria

• Patients with masses of major retroperitoneal organs
• Patients with retroperitoneal lymph nodal masses
• Patients with traumatic masses
• Patients with altered renal parameters are excluded from the study as intravenous contrast agent cannot be administered in such patients
• Patients with sensitivity to contrast agent (allergic reactions)
• Patients in whom a CT examination is contraindicated (Example: Pregnancy)
• Patients in whom MRI is contraindicated
• FNAC will not be done in patients with history of bleeding diathesis and in those not giving consent

After obtaining ethical clearance from the institutional committee, patients visiting or referred to the Department of Radiodiagnosis, KIMS Hubballi for the evaluation of primary retroperitoneal masses and those detected incidentally by routine ultrasonography of abdomen, were included in this study. A pre-designed semi-structured proforma, which was internally validated was used to collect the necessary information on all the needed variables.

Technique

• Multi Detector Computed Tomography imaging is performed on HITACHI 128 slice MDCT machine with thin slices in axial plane with reconstruction done. These findings are correlated with FNAC / histopathological examination.

Protocol

All patients were placed in supine position with arms extended above the level of head. Plain and post-contrast study of the abdomen and pelvis is done. Bowel opacification is achieved orally with 1000ml of diluted contrast for differentiating fluid filled bowel loops.

Acquisition of contiguous axial sections, of 5mm thickness of abdomen and pelvis in cranio-caudal direction from the level of the xiphisternum to pubis symphysis before and after administration of iodinated intravenous contrast was done. IV contrast opacification is achieved with 100-120ml of non-ionic contrast media (1-1.5ml/kg body weight) by infusing at the rate of 3ml/sec followed by arterial phase at 20-40 seconds and venous phase at 70-90 seconds. The delayed phase is acquired after a delay of 180 seconds after the arterial phase. Reconstruction was done with a slice thickness of 1 mm. All images are viewed in a range of soft tissue window setting. MRI was performed on MAGNETOM AVANTO ECO–SEIMENS 1.5 T MACHINE.

Data was entered into Microsoft excel data sheet and was analyzed using SPSS 22 version software. Categorical data was represented in the form of Frequencies and proportions. Chi-square test was used as test of significance for qualitative data. Fischer’s exact test was used as test of significance for qualitative data which does not fulfill the criteria for Chi-square test (2x2 tables only). Yates correction was applied where ever chi-square rules were not fulfilled (for 2x2 tables only). P value less than 0.5 was considered as statistically significant.

In the study, majority of the subjects belonged to the age group of 46 to 60 years (30.2%) followed by age group was 31 to 45 years, and more than 60 years (23.3 % each). The mean age was 44.26 ± 19.46 years. In the study, majority of the subjects were males (60.5%), and the remaining were females (39.5%).

Table 1: General characteristics

Based on FNAC/ histopathological diagnosis in the study, the most commonly reported condition was found to be liposarcoma (14.0%), on combining the sub-types of the condition. The next common conditions were found to be leiomyosarcoma and paraganglioma with the equal proportions of 9.3%. Based on FNAC/ histopathological diagnosis in the study, majority of the subjects were diagnosed with malignant condition (60.5%), and the remaining were benign masses (39.5%).

Table 2: FNAC/ Histopathological diagnosis of the study subjects

On observing the invasion of the mass, the study found local invasion and vascular involvement in 14.0% and 9.3% cases respectively. The lymph node metastasis was evident in only 1 individual, while 2 cases showed distant metastasis.

Table 3: Distribution of the study subjects based on invasion of the mass

Based on cross-sectional imaging in the study, the most commonly reported condition was found to be primary retroperitoneal tumor (16.3%), where the specific diagnosis was unavailable. The next common conditions were found to be liposarcoma and IVC leiomyosarcoma with the equal proportions of 14.0%. MRI don’t add any additional information other than CT; it is useful only in those cases in which CT is contraindicated. Accordingly, only 4 cases were subjected to MRI.

Table 4: Radiological diagnosis of the study subjects

In the study, majority of the subjects were males in the age group of 46 to 60 years, irrespective of the diagnosis. Thus the study found no significant association of age and gender of the subjects with the diagnosis of the condition, thereby implying that the age and gender of the subjects don’t necessarily alter with respect to the diagnosis of primary retroperitoneal masses.

Table 5: Association between the characteristics of the subjects and diagnosis of the condition

In the study, left paramedian region was involved by majority of benign conditions, while right paramedian region was involved by majority of malignant conditions. However, the study found no significant difference with respect to site of involvement. On other hand, the study found statistically significant association of enhancement of mass with the diagnosis of the condition, thereby implying that the enhancement significantly varies with respect to the diagnosis of primary retroperitoneal masses.

Table 6: Association of the site of involvement and enhancement of the mass with respect to the diagnosis of the condition

Based on radiological findings, soft tissue and fat components were observed in 88.4% and 20.9% respectively. The calcification, necrosis and hemorrhage were present in 30.2%, 58.1% and 14.0% respectively. About 25.6% cases were found to be cystic in nature.

On analyzing the association between the characteristics of the mass and diagnosis of the condition, the study found statistically significant relation only in terms of soft tissue component and necrosis, where malignant retroperitoneal masses showed soft tissue component and necrosis in majority cases comparatively.

Table 7: Association between the characteristics of the mass and diagnosis of the condition

On comparing the diagnosis of the primary retroperitoneal masses by cross-sectional imaging with the gold standard FNAC/HPE diagnosis, majority cases (74.4%) were accurately diagnosed. However, 4 cases were misdiagnosed, while specific diagnosis was not available in remaining 7 cases.

Table 8: Distribution of the study subjects based on the correctness in radiological diagnosis

In the study, there was perfect agreement in diagnosing the malignant primary retroperitoneal masses between cross-sectional imaging and HPE assessment. Also the study found statistically significant relation, where both sensitivity and specificity were estimated to be 100.0%, with 100.0% diagnostic accuracy.

Table 9: Validity of radiological investigation in diagnosing benign condition

Kappa agreement = 1.000

p-value <0.001* (Statistically significant)

In the present study, majority of the subjects belonged to the age group of 46 to 60 years (30.2%). On comparison with the previous literature, primary retroperitoneal masses were found to be more common in older adults. This can be justified from the comparison of the mean ages with the previous studies such as Cheng W et al.,⁹ (47.00 years), Manoj MC et al.,¹⁰ (50.40 years), Shalaan A et al.,³ (52.00 years), Lu J et al.,¹¹ (54.00 years) & Morosi C et al.,¹² (58.50 years).

Based on FNAC/ histopathological diagnosis in the present study, the most commonly reported condition was found to be liposarcoma (14.0%), whereas based on cross-sectional imaging, the most commonly reported condition was found to be primary retroperitoneal tumor (16.3%), where the specific diagnosis was unavailable. Even from most of the previous studies as Lu J et al.,¹¹ Cheng W et al.,⁹ and Morosi C et al.,¹² the commonest primary retroperitoneal tumor was diagnosed to be liposarcoma with the proportions of 61.7%, 30.1% and 35.4% respectively.

Based on FNAC/ histopathological diagnosis in the present study, majority were diagnosed with malignant condition (55.8%), and the remaining were benign masses (44.2%). This resembles the findings in the previous studies such as Baessler B et al.,¹³ and Shalaan A et al.², where the malignant cases were more frequent with the proportions of 55.0% and 60.0% respectively. Few studies such as Cheng W et al.,⁹ and Morosi C et al.,¹² had found equal proportions of benign and malignant cases on observation.

The present study also found statistically significant association of enhancement of mass and presence of soft tissue component with the diagnosis of the condition, where malignant retroperitoneal masses showed enhancement and soft tissue component in majority cases comparatively.

Further on comparing the diagnosis of the primary retroperitoneal masses by cross- sectional imaging with the gold standard HPE diagnosis, majority cases (74.4%) were accurately diagnosed. However, 4 cases were misdiagnosed, while specific diagnosis was not available in remaining 7 cases. Also, there was perfect agreement in diagnosing the primary retroperitoneal masses between cross-sectional imaging and HPE assessment. The study found statistically significant relation, with 100.0% diagnostic accuracy. This has been better in

comparison with the accuracy observed in the studies such as Shalaan A et al.², Cheng W et al.⁹, Morosi C et al.,¹² with the proportions of 69.7%, 70.0%, 86.7% respectively.

Cross-sectional imaging has been found to be very precise tool in diagnosing the primary retroperitoneal masses, and hence the study recommends use of this tool in future studies on larger sample of population. However, assigning a specific diagnosis for every mass lesion might be difficult, considering the overlapping imaging features, but based on characteristic features and relevant clinical information narrowing of differential diagnosis is possible. In addition to diagnosing the pathologies, cross-sectional imaging helps in staging and guided biopsies of the primary retroperitoneal masses. It also helps in assessment after radiotherapy or chemotherapy treatment.

Although the sample size is considerably adequate for the present study based on the availability of the cases in the study center, still higher sample size would have been better for generalizing the results. The duration of the study was sufficient enough for accurate assessment of the outcome in the study. However, other factors such as atypical presentation among the subjects which affects the clinical correlation, difference in investigator perception over the diagnosis of the condition etc., which may act as the bias in interpreting the results must also be considered.

Cross-sectional imaging is a useful imaging modality to localise, differentiate and diagnose the primary retroperitoneal masses. We conclude that it is possible to evaluate the nature, morphology and extent of the mass and its relationship to adjacent structures using cross-sectional imaging. Further, based on the characteristic imaging features and on correlating it with relevant clinical information, it is possible to narrow down the differential diagnosis of primary retroperitoneal masses whenever assigning a specific diagnosis is difficult due to overlapping imaging features.

Conflict of Interest: None to declare

Source of funding: Nil

1. Armstrong JR, Cohn I Jr. Primary malignant retroperitoneal tumors. Am J Surg 1965;110(6):937–943.
2. Shalaan A, Refaat M, Farouk H, Saleh GS. Role of multislice computed tomography in characterization of different retroperitoneal masses. Tanta Medical Journal. 2017 Jan 1;45(1):1.
3. Gâtita CE, Georgescu I, Nemes R. Difficulties in diagnosis of primitive retroperitoneal tumors. Current Health Sciences Journal. 2010;36:132–135.
4. Caraiani C, Yi D, Petresc B, Dietrich C. Indications for abdominal imaging: When and what to choose? Journal of ultrasonography. 2020 Apr 1;20(80):43-54.
5. Mukhtar S, Khan SA, Hussain M, Adil Role of multidetector computed tomography in evaluation of ovarian lesions in women clinically suspected of malignancy. Asian Pacific Journal of Cancer Prevention: APJCP. 2017;18(8):2059.
6. Andrzejewska M, Grzymisławski M. The role of intestinal ultrasound in diagnostics of bowel diseases. Gastroenterology Review/Przegląd Gastroenterologiczny. 2018 Mar 26;13(1):1-5.
7. Singhal S, Prabhu NK, Sethi P, Moorthy Role of multi detector computed tomography (MDCT) in preoperative staging of pancreatic carcinoma. Journal of Clinical and Diagnostic Research: JCDR. 2017 May;11(5):TC01.
8. Meeks SL, Harmon Jr JF, Langen KM, Willoughby TR, Wagner TH, Kupelian PA. Performance characterization of megavoltage computed tomography imaging on a helical tomotherapy unit. Medical physics. 2005 Aug;32(8):2673-81.
9. Cheng W, Qi Y, Wang B, Tian L, Huang W, Chen Y. Characteristics and computed tomography evaluation of primary retroperitoneal tumours: report of 113 cases. The Annals of The Royal College of Surgeons of England. 2017 Jan;99(1):55-9.
10. Manoj MC, Prabhu CS, Lokesh T. A comparative evaluation of ultrasonography versus computed tomography in the assessment of retroperitoneal masses. Trauma. 2021;4:6.
11. Lu J, Qin Q, Zhan LL, Yang X, Xu Q, Yu J, Dou LN, Zhang H, Yang Y, Chen XC, Yang YH. Computed tomography manifestations of histologic subtypes of retroperitoneal liposarcoma. Asian Pacific journal of cancer prevention. 2014;15(15):6041-6.
12. Morosi C, Stacchiotti S, Marchianò A, Bianchi A, Radaelli S, Sanfilippo R, Colombo C, Richardson C, Collini P, Barisella M, Casali PG. Correlation between radiological assessment and histopathological diagnosis in retroperitoneal tumors: analysis of 291 consecutive patients at a tertiary reference sarcoma center. European Journal of Surgical Oncology (EJSO). 2014 Dec 1;40(12):1662-70.
13. Baessler B, Nestler T, Pinto dos Santos D, Paffenholz P, Zeuch V, Pfister D, Maintz D, Heidenreich A. Radiomics allows for detection of benign and malignant histopathology in patients with metastatic testicular germ cell tumors prior to post-chemotherapy retroperitoneal lymph node dissection. European Radiology. 2020 Apr;30(4):2334-45.