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 Table of Contents  
ORIGINAL ARTICLE
Year : 2017  |  Volume : 45  |  Issue : 1  |  Page : 1-7

Role of multislice computed tomography in characterization of different retroperitoneal masses


1 Radiology Department, Benha University, Benha, Egypt
2 General Surgery Department, Benha University, Benha, Egypt

Date of Submission10-Jan-2017
Date of Acceptance04-Feb-2017
Date of Web Publication28-Jun-2017

Correspondence Address:
Ahmed Shalaan
Radiology Department, Benha University
Egypt
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DOI: 10.4103/tmj.tmj_1_17

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  Abstract 


Background
Multislice computed tomography imaging (MSCT) plays an integral role in the characterization of primary retroperitoneal masses and in the evaluation of their extent and involvement of adjacent structures, and therefore in treatment planning. Many authors have described useful imaging features to distinguish between the different entities.
Aim
The aim of this study was to evaluate the role of MSCT in differentiation of primary retroperitoneal masses in correlation with pathological findings.
Patients and methods
This prospective study was performed on 43 patients aiming to determine the role of cross-sectional computed tomography (CT) imaging in the differential diagnosis of primary retroperitoneal masses. Each case was submitted for pathological analysis either following open surgical biopsy, surgical excision, or image-guided biopsy by CT or ultrasound. Correlation of CT findings with pathological results was obtained.
Results
The calculated accuracy for the diagnosis and differential diagnosis of primary retroperitoneal masses by MSCT was 69.7% in the studied cases matched with pathological findings, which represented 30 cases of our study. This was helpful in narrowing the differential diagnosis and thus in treatment planning.
Conclusion
Multi-slice Computed Tomography (MSCT) is considered the basic standard in morphological evaluation, and the diagnosis of primary retroperitoneal masses according to their origin is carried out first and then characterization of the mass lesion is performed depending upon the specific imaging characteristics detected on CT examination such as consistency, component, vascularity and enhancement pattern, as well as specific pattern of spread.

Keywords: multislice computed tomography, primary retroperitoneal masses, standard of reference


How to cite this article:
Shalaan A, Refaat M, Farouk H, Saleh GS. Role of multislice computed tomography in characterization of different retroperitoneal masses. Tanta Med J 2017;45:1-7

How to cite this URL:
Shalaan A, Refaat M, Farouk H, Saleh GS. Role of multislice computed tomography in characterization of different retroperitoneal masses. Tanta Med J [serial online] 2017 [cited 2017 Dec 12];45:1-7. Available from: http://www.tdj.eg.net/text.asp?2017/45/1/1/209094




  Introduction Top


Primary retroperitoneal neoplasms are a diverse group of benign and malignant tumors that arise within the retroperitoneum but outside the major organs [1]. Although computed tomography (CT) imaging can demonstrate important characteristics of these tumors, diagnosis is often challenging for radiologists. Diagnostic challenges include precise localization of the lesion, determination of the extent of invasion, and characterization of the specific pathologic type [1]. Of the primary retroperitoneal neoplasms, 70–80% are malignant in nature, and these account for 0.1–0.2% of all malignancies in the body [2]. CT is the preferred modality in imaging of the retroperitoneum. The attenuation differences between retroperitoneal fat and organs increase the diagnostic accuracy of CT in detection of retroperitoneal diseases [3].

Familiarity with retroperitoneal anatomy and the radiographic signs to identify an intra-abdominal mass as primary retroperitoneal enable differentiation between primary and secondary masses. The differential diagnosis of primary retroperitoneal masses may be based on the predominant cross-sectional imaging appearance as either cystic or solid and neoplastic or non-neoplastic. Characteristic imaging findings, such as the composition, enhancement pattern, location, and relationship to adjacent structures, may be combined with clinical information to help narrow the differential diagnosis [4].

Anatomy of retroperitoneal space

The retroperitoneum is a complex compartment, the anatomy of which has yet to be fully validated [5]. The currently accepted model of the retroperitoneum anatomy has been proposed by Meyers, anatomy of the retroperitoneum. Imaging 12.1, 10–20, 1974, 1994, who led to an enhanced understanding of retroperitoneal anatomy and pathology [6]. The retroperitoneum is the compartmentalized space bounded anteriorly by the posterior parietal peritoneum and posteriorly by the transversalis fascia. It extends from the diaphragm superiorly to the pelvic brim inferiorly. The abdominal retroperitoneum is divided by fascial planes into the anterior and posterior pararenal spaces and the perirenal (or perinephric) space [8] ([Figure 1] and [Figure 2]).
Figure 1 Drawing of the anatomy of the retroperitoneal spaces at the level of the kidneys. The anterior pararenal space (APRS) is located between the parietal peritoneum (PP) and the anterior renal fascia (ARF) and contains the pancreas (Pan), the ascending colon (AC), and the descending colon (DC). The posterior pararenal space (PPRS) is located between the posterior renal fascia (PRF) and the transversalis fascia (TF). The perirenal space (PRS) is located between the anterior renal fascia and the posterior renal fascia. Ao, aorta; IVC, inferior vena cava; LCF, lateroconal fascia [7]

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Figure 2 Diagram of the left retroperitoneal space detailing the fasciae and compartments [5]

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The renal fasciae, namely, the anterior and posterior renal fasciae, represent the fundamental anatomical structures for the division of the retroperitoneal space, and they are clearly visible on CT imaging ([Figure 3]). The renal fasciae are usually not thicker than 3 mm. If renal fasciae appear thicker than 3 mm, this is often because of a retroperitoneal space disease, corresponding mainly to acute pancreatitis, renal pathologies, and abdominal aorta aneurysm rupture [6]. Because of loose connective tissue in the retroperitoneum, tumors can have widespread extension before clinical presentation [9].
Figure 3 Computed tomography: anatomy of the retroperitoneal space. AA, abdominal aorta; ARF, anterior renal fascia; DC, descending colon; IVC, inferior vena cava; LCF, lateroconal fascia; PRF, posterior renal fascia; PM, psoas muscle; QL, quadratus lumborum muscle; UR, ureter [6]

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  Patients and methods Top


Study design

This prospective study was performed aiming to determine the role of multislice computed tomography imaging (MSCT) imaging in the differential diagnosis of primary retroperitoneal masses.

Study population

The study was performed at Benha University Hospital, National Cancer Institute, and informed consents were given by all patients. The study was conducted on 43 patients (24 male and 19 female and mean age, 52 years) who presented with abdominal or pelvic swelling (on clinical examination or detected by previous imaging studies) suspected to be of retroperitoneal origin between January 2015 until august 2016, to perform CT abdomen and pelvis for initial assessment or follow-up.

Inclusion criteria

Patients with retroperitoneal mass lesions were included.

Exclusion criteria

The exclusion criteria were as follows:
  1. Patients with lesions not located at the retroperitoneal region.
  2. Patients with retroperitoneal lesion originating from retroperitoneal organs (e.g. kidneys, adrenal glands, and pancreas).
  3. Pregnant patients.
  4. Patients with unstable general condition.


Multi-Slice Computed Tomography (MSCT) abdomen and pelvis abdomen and pelvis was done.

Computed tomography examination protocol design

CT exams were performed on a General electric light speed volumetric Computed Tomography 64 multi-slice computed tomography scanner and Toshiba Asteion 4 slice CT scanner : Leader health care; Egypt.

CT abdomen and pelvis with oral and intravenous contrast was performed using the following parameters: 350 mA, 120 kV, 0.5 s tube rotation time, slice thickness 5 mm, 8 mm table feed, and 3 mm incremental reconstruction.

Noncontrast CT was performed in patients with impaired renal function (creatinine level >2 mg/dl) and/or in those who have a history of hypersensitivity for contrast media.

Patient preparation for computed tomography examinations

All patients were asked to fast for 6 h before the scan. All metallic items were removed from the patient, including pants with zipper, etc., and the patients were given a gown to wear. An intravenous cannula was inserted in the patient’s arm for administration of contrast.

Computed tomography image interpretation

The CT data were evaluated by two experienced radiologists in consensus; both observers were unaware of the pathological data of each patient.

Computed tomography images

On CT, confirming the site as retroperitoneal was done first, followed by assessment of definition, consistency, components of the lesion (fat, calcium, necrosis), pattern of enhancement (unenhanced, homogeneous or heterogeneous), and average CT attenuation (by measuring Housefield Unit (HU) in five different locations and calculating the average HU).

CT is performed starting with the abdominal or pelvic mass followed by differentiation of solid primary retroperitoneal masses according to location, pattern of spread, vascularity, and composition. The cystic lesions were differentiated according to the site, specific imaging characteristics, and clinical history.

Computed tomography images interpretation

In each case the CT imaging features of the lesions were interpreted as described above, resulting in either reaching the most probable diagnosis, two differential diagnoses, more than two differential diagnoses, or failed to reach definite diagnosis.

Correlation of these results with pathological data was then done.

Standard of reference

All cases were submitted for pathological analysis either following open surgical biopsy, surgical excision, or image-guided biopsy by CT or ultrasound. Pathological data were taken as the standard of reference.


  Results Top


A total of 43 patients presented with abdominal or pelvic swelling (detected by clinical examination or by previous imaging study suspected to be of retroperitoneal origin); the mean±SD disease duration was 13.4±10.4 years and their mean age was 31.75±21.48 years.

On CT, confirming site as retroperitoneal and excluding organ of origin was done first, followed by assessment of definition ([Table 1]), consistency, components of the lesion (fat, calcium, necrosis), pattern of enhancement (unenhanced, homogeneous, or heterogeneous), vascularity, and average CT attenuation (by measuring HU in five different locations and calculating the average HU).
Table 1 Computed tomography definition of the examined lesions

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Regarding the consistency

  1. Nine lesions were purely cystic: lymphocele (n=2), simple cysts (n=2), lymphangioma (n=2), mucinous cystadenoma (n=2), and pancreatic pseudocysts (n=1).
  2. Six lesions were mixed solid and cystic: ganglioneuroma (n=1), pseudomyxoma peritoneii (n=1), teratoma (n=3), and schwannoma (n=1).
  3. The rest of the lesions were solid ([Table 2]).
    Table 2 Consistency of the computed tomography examined lesions

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Regarding the composition

  1. Fat: eight lesions contained fat, three of which were liposarcoma, three were teratoma, and two lesions were lipoma.
  2. Calcification: twelve lesions contain calcifications as follows: neuroblastoma (n=5), liposarcoma (n=1), myofibroblastic tumor (n=1), primary germ cell tumor (n=1), mucinous cystadenoma (n=1), teratoma (n=2), and ganglioneuroma (n=1).
  3. Necrosis: fifteen lesions show internal necrosis as follows: neuroblastoma (n=4), paraganglioma (n=2), liposarcoma (n=2), lieomyosarcoma (n=1), myofibroblastic tumor (n=1), primary germ cell tumor (n=1), undifferentiated sarcoma (n=2), schwannoma (n=1), lymphoma (n=1), spindle cell sarcoma (n=1), and metastatic lymph node (n=1) ([Table 3]).
    Table 3 Components of the computed tomography examined lesions

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Regarding the vascularity of the lesions

  1. Hypervascularity: only one lesion was hypervascular, which was a paraganglioma.
  2. No or hypovascularity: 20 lesions show no or hypovascularity as follows: retroperitoneal fibrosis (n=1), liposarcoma (n=3), schwannoma (n=1), lymphoma (n=4), ganglioneuroma (n=1), mucinous cystadenoma (n=1), pancreatic pseudocysts (n=1), neuroblastoma (n=1), lymphangioma (n=1), cystic mesotheliomas (n=2), lipoma (n=2), and lymphocele (n=2).
  3. Moderate vascularity: the rest of the lesions show moderate vascularity ([Table 4]).
    Table 4 Vascularity of the computed tomography examined lesions

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Regarding lesion enhancement

  1. Eleven lesions were unenhanced as follows: retroperitoneal fibrosis (n=1), lymphocele (n=2), schwannoma (n=1), pancreatic pseudocysts (n=1), neuroblastoma (n=1), lymphangioma (n=1), cystic mesotheliomas (n=2), and lipoma (n=2).
  2. Five lesions show homogeneous enhancement as follows: paraganglioma (n=1), which was markedly enhanced, and lymphoma (n=4), which was mildly enhanced.
  3. The rest of the lesions show heterogeneous enhancement ([Table 5]).
    Table 5 Enhancement of the computed tomography examined lesions

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Matching of pathological diagnosis and computed tomography imaging diagnosis

  1. Twenty-five lesions matched the only diagnosis by CT as follows: liposarcomas (n=3), lymphomas (n=4), neuroblastoma (n=3), retroperitoneal fibrosis (n=1), lymphoceles (n=2), paraganglioma (n=1). Retropertoneal metastatic lymph node (n=2), cystic mesotheliomas (n=2), lipoma (n=2), lymphangioma (n=1), teratoma (n=3), and pancreatic pseudocysts (n=1).
  2. Five lesions matched two differential diagnoses by CT as follows: neuroblastoma (n=1), ganglioneuroma (n=1), schwannoma (n=2), and mucinous cystadenoma (n=1).
  3. Three lesions were one of more than two differential diagnoses by CT as follows: neuroblastoma (n=1), the pseudomyxoma retroperitonei (n=1), and myofibroblastic tumor (n=1).
  4. Ten lesions did not match the pathological diagnosis as follows: lymphoma (n=1), myofibroblastic tumor (n=2), other sarcomas (n=6), and primary germ cell tumor (n=1) ([Table 6]).
    Table 6 Matching of pathological diagnosis and computed tomography imaging diagnosis

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The ability of computed tomography to narrow the differential diagnosis of primary retroperitoneal masses

  1. Positive: if the pathological diagnosis matched with the only diagnosis by CT or was one of two differential diagnoses by CT, the result was positive.
  2. Negative: if the pathological diagnosis was one of more than two differential diagnoses by CT, was not included as differential diagnosis by CT, or no definite diagnosis was reached by CT, the result was negative ([Table 7]).
    Table 7 Ability of multidetector computed tomography to narrow the differential diagnosis

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Positive results include 30 lesions and negative results include 13 lesionswith the accuracy of 69.7% ([Figure 4],[Figure 5],[Figure 6],[Figure 7],[Figure 8],[Figure 9],[Figure 10]).
Figure 4 Axial contrast-enhanced computed tomography scan of a 61-year-old male patient with retroperitoneal fibrosis shows mantle-like lesion encasing the aorta and inferior vena cava, as well as medial deviation of both ureters toward the lesion. Bilateral double J catheters are seen

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Figure 5 Postcontrast computed tomography scan of a 50-year-old male patient with Hodgkin’s lymphoma. Axial cut shows large isodense soft tissue with no necrotic changes or calcification, and no significant contrast enhancement detected

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Figure 6 Postcontrast computed tomography scan of a 4.5-year-old female patient with neuroblastoma. Axial cut revealed a large left retroperitoneal mass with dense scattered calcifications and heterogeneous enhancement

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Figure 7 Postcontrast computed tomography scan of a 23-year-old woman with paraganglioma. Axial cut shows large hypervascular mass lesion with internal necrosis, as well as dense contrast enhancement

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Figure 8 Contrast-enhanced computed tomography scan of a 22-year-old woman showing retroperitoneal lipoma. Axial cut shows anterior and leftward displacement of the small bowel loops by a large right iliac well-defined lobulated fat containing lesion with no calcification within

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Figure 9 Contrast-enhanced computed tomography scan of a 53-year-old woman showing retroperitoneal teratoma. Axial cut shows anterior displacement of the pancreas by a well-defined mixed mass lesion (soft tissue and fat attenuation) with calcification within

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Figure 10 Contrast-enhanced computed tomography scan of a 53-year-old woman with malignant fibrous histiocytoma revealed large right lumbar retroperitoneal mass with scattered calcifications and faint enhancement

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  Discussion Top


Diagnosis of a primary retroperitoneal mass may be made once the location is confirmed as within the retroperitoneal space and after an organ of origin is excluded.

Although CT imaging can demonstrate important characteristics of these tumors, diagnosis is often challenging for radiologists. Diagnostic challenges include precise localization of the lesion, determination of the extent of invasion, and characterization of the specific pathologic type.

The differential diagnosis of primary retroperitoneal masses may be based on the predominant CT imaging appearance as either cystic or solid and neoplastic or non-neoplastic.

Characteristic imaging findings, such as the composition (fat, calcification, and necrosis), enhancement pattern, vascularity, location, and relationship to adjacent structures, may be combined with clinical information to help narrow the differential diagnosis.

In each case of our patients, the CT imaging features of the lesions were interpreted by two experienced radiologists, resulting in either reaching the most probable diagnosis, two differential diagnoses, more than two differential diagnoses, or failed to reach definite diagnosis.

Correlation of these results with pathological data was then done. The accuracy of CT assisted by the postulated scheme to narrow the differential diagnosis was 69.7%.

Our study was carried out on 43 cases; most of them were suspected to be of retroperitoneal origin (location), and the rest of them were accidentally discovered. These cases were classified as primary retroperitoneal origin into solid and cystic masses.

Most of the previous studies were assessing the ability of CT in the diagnosis of retroperitoneal masses regarding exact localization and being benign or malignant, without reaching the exact diagnosis or narrowing the differential diagnosis of the primary retroperitoneal mass.

Lane et al. [10] in their study, reviewed CT scans obtained at initial presentation in 90 patients with primary retroperitoneal neoplasms. Pathologic specimens and clinical histories were reviewed and correlated with CT findings. They concluded that although CT is nonspecific in many cases a number of CT features and clinical findings may suggest specific diagnoses when present: (a) the presence of calcification in malignant fibrous histiocytoma; (b) the presence of fat in a mass lesion of heterogeneous density in liposarcoma; (c) large regions of necrosis in leiomyosarcoma; (d) calcified tumor in a child in neuroblastoma; (e) hypervascularity of hemangioma and hemangiopericytoma; (f) catecholamine excess and para-aortic location in paraganglioma; (g) homogeneous, low density of neurofibroma; (h) homogeneous, fat density of lipoma; and (i) characteristic mixed components of teratoma.

The clinical findings and radiological features of 25 patients with primary retroperitoneal tumors were retrospectively evaluated in a study conducted by Nakashima [11] to find the signs that might contribute to the preoperative distinction between benign and malignant tumors. Of 25 primary retroperitoneal tumors, 15 were benign. A retroperitoneal tumor scoring system was developed to distinguish primary retroperitoneal benign tumors from their malignant counterparts based on the following: (a) maximum diameter equal to or larger than 5.5 cm; (b) presence of symptoms; (c) absence of calcification; (d) presence of irregular margins; and (e) presence of cystic degeneration or necrosis. Their study suggests that the size of tumor, the presence of symptoms, irregular margins, and the absence of calcification may be valuable predictors of primary retroperitoneal malignant tumor.

As discussed above, most of the previous studies were assessing the ability of CT in the diagnosis of retroperitoneal masses regarding exact localization and being benign or malignant. However, our study is considered unique in reaching the exact diagnosis or narrowing the differential diagnosis of the primary retroperitoneal masses.





Familiarity with retroperitoneal anatomy and the radiographic signs to identify an intra-abdominal mass as primary retroperitoneal enable differentiation between primary and secondary masses.

The differential diagnosis of primary retroperitoneal masses may be based on the predominant cross-sectional CT imaging appearance as either cystic or solid and neoplastic or non-neoplastic.

Characteristic imaging findings, such as the composition (fat, calcification, and necrosis), enhancement pattern, vascularity, location, and relationship to adjacent structures, may be combined with clinical information to narrow the differential diagnosis.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

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Nishino M, Hayakawa K, Minami M, Yamamoto A, Ueda H, Takasu H. Primary retroperitoneal neoplasms: CT and MR imaging findings with anatomic and pathologic diagnostic clues 1. Radiographics 2003; 23:45–57.  Back to cited text no. 1
    
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Neville A, Herts BR. CT characteristics of primary retroperitoneal neoplasms. Crit Rev Comput Tomogr 2004; 45:247–270.  Back to cited text no. 2
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Ramchandani P, Drew T, Dogra VS, Onur MR. Benign and malignant masses of the retroperitoneum. Abdominal imaging. Berlin Heidelberg: Springer 2013. pp. 1693–1724.  Back to cited text no. 3
    
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Scali EP, Chandler TM, Hefferman EJ, Coyle J. Primary retroperitoneal masses: what is the differential diagnosis? Abdom Imaging 2014; 40:1–17.  Back to cited text no. 4
    
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Burkill GJC, Healy JC. Anatomy of the retroperitoneum. Imaging 2000; 12:10–20.  Back to cited text no. 5
    
6.
Quaia E, Gennari AG. Normal radiological anatomy of the retroperitoneum. Radiological imaging of the kidney. Berlin Heidelberg: Springer 2014. pp. 75–79.  Back to cited text no. 6
    
7.
Rajiah P, Rakesh S. Imaging of uncommon retroperitoneal masses. Radiographics 2011; 31:949–976.  Back to cited text no. 7
    
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Goenka AH, Shah SN, Remer EM. Imaging of the retroperitoneum. Radiol Clin North Am 2012; 50:333–355.  Back to cited text no. 8
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Koh DM, Moskovic E. Imaging tumours of the retroperitoneum. Imaging 2000; 12:49–60.  Back to cited text no. 9
    
10.
Lane RH, Stephens DH, Reiman HM. Primary retroperitoneal neoplasms: CT findings in 90 cases with clinical and pathologic correlation. Am J Roentgenol 1989; 152:83–89.  Back to cited text no. 10
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11.
Nakashima J, Ueno M, Nakamura K. Differential diagnosis of primary benign and malignant retroperitoneal tumors. Int J Urol 1997; 4:441–446.  Back to cited text no. 11
    


    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7]



 

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