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ECR 2019 / C-1433
Cum Laude
Primary retroperitoneal tumors, Can we narrow the differential diagnosis?
Congress: ECR 2019
Poster No.: C-1433
Type: Educational Exhibit
Keywords: Retroperitoneum, Oncology, CT, MR, Diagnostic procedure, Cancer, Pathology
Authors: A. H. A. Mohamed, H. Wahba, S. A. A. Z. Hanna; Cairo/EG
DOI:10.26044/ecr2019/C-1433

Findings and procedure details

Approach to retroperitoneal masses

The majority of retroperitoneal masses arises from retroperitoneal organs and is therefore not considered primary retroperitoneal mass. 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.

1.Tumor location (Determining tumor location into the retroperitoneal spaces)

Displacement of normal retroperitoneal structures, such as retroperitoneal organs or vascular structures, suggests that a mass is retroperitoneal in location (Fig. 5). Nevertheless, determining retroperitoneal tumor location could be difficult in case of big masses or mesenterial lesions.

Fig. 5: Anterior displacement of retroperitoneal structures suggests that a mass arises in the retroperitoneum, with anterior displacement of the kidney for lateral masses (Malignant fibrous histiocytoma).
References: Cardone, et al. (2011) "Retroperitoneal tumors: Computed Tomography (CT) and Magnetic Resonance (MR) patterns" ECR 2011. Austria Center Vienna, Vienna, Austria,. Poster presentation

2.Excluding organ of origin

In order to classify a mass as primary retroperitoneal, the possibility that it arises from a retroperitoneal organ must be excluded. Several radiographic signs are instructive:

  • Claw or beak sign.
  • Embedded organ sign.
  • Invisible organ sign (phantom organ sign).
  • Prominent Feeding Artery Sign.
  • Claw or beak sign: A mass that originates from a particular organ will form acute angles with it and at least partially surround it in the shape of a claw or beak . Conversely, if the mass originates from a structure adjacent to the organ, it will form obtuse angles to abut and compress the organ (Fig 6 , 7). 
Fig. 6: Beak sign. (a, b) Drawings illustrate the positive beak sign (a), in which Tumor A arises from Organ B, and the negative beak sign (b), in which Tumor A does not arise from Organ B.
References: Nishino et al. (2003) "Primary Retroperitoneal Neoplasms: CT and MR Imaging Findings with Anatomic and Pathologic Diagnostic Clues 1." Radiographics 23.1; 45-57.‏
Fig. 7: Positive beak sign: diagram (A) and CT scan after CM administration (B). The appearance is supported by parenchymal tokens that “envelop” the tumor. The lesion originates from the organ (renal mass).Negative beak sign: diagram (C) and CT scan after contrast medium administration (D). The tumor does not originate from the organ, which is also compressed. An acute angle forms at the contact points between the resident organ and the lesion as shown in (c) (primary retroperitoneal mass).
References: Carbognin et al (2005). "Retroperitoneal tumors." Radiologic-Pathologic Correlations from Head to Toe. Springer Berlin Heidelberg; 619-643.‏
  • Embedded organ sign: (Fig 8) A mass that arises from a given organ often appears embedded within in and the interface between the two may be difficult to appreciate (Fig. 10). Conversely, a mass that abuts but does not originate from a hollow structure compresses it to produce a crescentic deformity (Fig 9) (.
Fig. 8: Embedded organ sign. (a, b) Drawings illustrate the negative embedded organ sign (a), in which Tumor A simply compresses Organ B, and the positive embedded organ sign (b), in which Tumor A arises from Organ B so that the organ appears to be embedded in the tumor.
References: Nishino et al. (2003) "Primary Retroperitoneal Neoplasms: CT and MR Imaging Findings with Anatomic and Pathologic Diagnostic Clues 1." Radiographics 23.1; 45-57.‏
Fig. 9: Negative embedded organ sign: diagram (G) and CT scan after CM administration (H). The wall of a hollow viscus is compressed extrinsically from the tumor creating a crescent shape (arrowheads)
References: Carbognin et al (2005). "Retroperitoneal tumors." Radiologic-Pathologic Correlations from Head to Toe. Springer Berlin Heidelberg; 619-643.‏
  • Invisible organ sign (phantom organ sign): A large mass, particularly when arising from a small organ, may render the organ of origin undetectable (Fig 11).‏ Conversely, absence of the invisible organ sign suggests primary retroperitoneal pathology.
Fig. 11: Phantom organ sign: diagram (E) and CT scan after CM administration (F). The tumor’s originating organ (right kidney) appears totally incorporated by the tumor and is no longer recognizable (F).
References: Carbognin et al (2005). "Retroperitoneal tumors." Radiologic-Pathologic Correlations from Head to Toe. Springer Berlin Heidelberg; 619-643.‏
  • Prominent Feeding Artery Sign: Hypervascular masses are often supplied by feeding arteries that are prominent enough to be visualized at CT or MR imaging, a finding that provides an important key to understanding the origin of the mass (Fig. 12).
Fig. 12: Prominent feeding artery sign, Axial CECT image of right renal cell carcinoma showing the mass being supplied by the right renal artery.
References: Bhargavi D. et al (2015). "MDCT signs differentiating retroperitoneal and intraperitoneal lesions- diagnostic pearls" ECR 2015. Austria Center Vienna, Vienna, Austria, Poster presentation

 

 

Diagnostic schemes and clues to help narrow the differential diagnosis of primary retroperitoneal lesions:

First step Is to determine the lesion is retroperitoneal (displacing retroperitoneal organs) and to exclude organ of origin (Fig. 13).

 

Fig. 13: A scheme for the approach to abdominal or pelvic mass lesion.
References: Radiology, National cancer institute - Cairo/EG

 

Then according to whether it is solid or cystic certain schemes will be followed. 

 

Solid retroperitoneal lesions 

  • Regarding the location and pattern of spread (Fig. 14).

 

Fig. 14: A scheme for the differential diagnosis of solid retroperitoneal lesions according to location and pattern of spread.
References: Radiology, National cancer institute - Cairo/EG
  • Regarding the vascularity (Fig. 15).

 

Fig. 15: Scheme for the differential diagnosis of solid retroperitoneal lesions according to vascularity.
References: Radiology, National cancer institute - Cairo/EG
  •  Regarding the characteristic tumoral components (Fat, calcifiaction, necrosis) (Fig. 16).
Fig. 16: A scheme for the differential diagnosis of solid retroperitoneal lesions according to composition (fat, calcifications or necrosis).
References: Radiology, National cancer institute - Cairo/EG
  • Regarding the small round cells composition (low T2 signal) (Fig 17).
  • At T2-weighted MR imaging, tumors composed of small round cells often appear as homogeneous masses with relatively hypointense areas representing densely packed cellular components. 
Fig. 17: A scheme for the differential diagnosis of solid retroperitoneal lesions having T2WI hypo-intense signal.
References: Radiology, National cancer institute - Cairo/EG

 

 

  • According to specific MRI signs (Fig 18):

 

  • Target sign: central area with a low or intermediate signal surrounded by a hyperintense ring in T2. Histologically it corresponds to fibrous tissue centrally and myxoid tissue around the edge. It is frequently seen in neurofibromas and schwannoma (target-sign-neurofibromas-Radiopedia).
  • Bowl of fruit sign: low intensity mosaic, intermediate and high signal in T2-weighted images due to a combination of solid components, cystic degeneration, hemorrhage,myxoid stroma and fibrous tissue. This is often seen in malignant fibrohistiocytoma, synovial sarcoma and Ewing’s sarcoma Fig. 22 .
  • Whorled appearance: a linear or curvilinear structure appearing hypointense in T2. It corresponds to a band of Schwann cells and collagen fiber in the mass. It is commonly seen in ganglioneuroma and neurofibroma  Fig. 24 .
  • Flow void: this is often seen in hemangiopericytoma, arteriovenous hemangioma and alveolar sarcoma of the soft tissues.
  • Speckled enhancement: this can be found in T1- weighted images after CM and corresponds to intratumoral structures similar to septa. It is more frequently seen in leiomyosarcoma and rhabdomyosarcoma.
Fig. 18: A scheme for the differential diagnosis of primary retroperitoneal solid lesions according to specific MRI signs.
References: Radiology, National cancer institute - Cairo/EG

 

 

Cystic primary retroperitoneal lesions:

  • Differential diagnosis according to the site (Fig 19).
  • Differential diganosis according to clinical history (Fig 20).
  • Differential diganosis according to specific imaging characteristics (Fig 21).

 

Fig. 19: A scheme for the differential diagnosis of cystic retroperitoneal lesions according to the site.
References: Radiology, National cancer institute - Cairo/EG

 

Fig. 20: A scheme for the differential diagnosis of cystic retroperitoneal lesions according to clinical history.
References: Radiology, National cancer institute - Cairo/EG

 

Fig. 21: A scheme for the differential diagnosis of cystic retroperitoneal lesions according to specific imaging characteristics.
References: Radiology, National cancer institute - Cairo/EG

 

 

Cases:

 

  • Case 1: Well differentiated liposarcoma (Fig. 23).
Fig. 23: Contrast enhanced CT scan of a 44 years old female with well differentiated liposarcoma. a. Axial cut showing anterior displacement of the right kidney with negative claw sign. b. Axial cut showing the lesion crossing the midline.
References: Radiology, National cancer institute - Cairo/EG
  • Case 2: Neurofibroma (Fig. 24).
Fig. 24: Contrast enhanced CT scan of 47 years old female patient with neurofibroma a,b) Axial T1WI and T2WI. c,d) Axial Diffusion weighted images and ADC. e,f) Axial T2 Fat suppressed images, and post contrast T1 fat suppressed images.
References: Radiology, National cancer institute - Cairo/EG
  • Case 3: Hodgkin lymphoma (Fig. 25).
Fig. 25: Contrast enhanced CT scan of 22 years old male with hodgkin lymphoma. a. Axial cut showing characteristic CT angiogram sign. b. Coronal reformatting showing mantle like lesion along the abdominal aorta
References: Radiology, National cancer institute - Cairo/EG
  • Case 4: Image findings of teratoma (yet no available pathology as patient refused surgery) (Fig. 26).
Fig. 26: Contrast enhanced CT scan of a 32 years old female. a. Axial cut showing anterior displacement of the pancreas by well-defined lesion with calcifications are noted within. b. Axial cut showing fluid-fluid and fat fluid level. c, d .Coronal and sagittal reformatting
References: Radiology, National cancer institute - Cairo/EG
  • Case 5: Ganglioneuroma (Fig. 27).
Fig. 27: Contrast enhanced CT scan of 26 years old female with ganglioneuroma. a. Axial cut showing rather well defined hypodense lesion. b. Axial cut showing anterior displacement of the pancreas anteriorly and posterolateral displacement of the right suprarenal gland. c.Coronal reformatting shows extension of the lesion along the sympathetic chain
References: Radiology, National cancer institute - Cairo/EG
  • Case 6: Paraganglioma (Fig. 28).
Fig. 28: Triphasic contrast enhanced CT scan of 45 years old female with paraganglioma. Axial cuts showing hypervascular lesion with internal areas of necrosis , presenting dense heterogeneous arterial (a) enhancement with subsequent filling in the portal (b) and delayed (c) phases.
References: Radiology, National cancer institute - Cairo/EG
  • Case 7: Retroperitoneal fibrosis (Fig. 29).
Fig. 29: Contrast enhanced CT scan of 60 years old male with retroperitoneal fibrosis. a) Axial cut showing bilateral renal backpressure changes with bilateral ureteric double J stents. b) Axial cut showing medial deviation of the ureters toward the lesion. c) Coronal reformatting showing mantle like lesion encasing the lower end of the aorta and IVC.
References: Radiology, National cancer institute - Cairo/EG
  •  Case 8: Lymphocele post radical cystectomy (Fig. 30).
Fig. 30: Contrast enhanced CT scan of 70 years old male with lymphocele a)Axial cut showing anterior displacement of the descending colon. b)Sagittal reformatted images.
References: Radiology, National cancer institute - Cairo/EG

 

 

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