Retroperitoneal masses: magnetic resonance imaging findings with pathologic correlation

Diagnostic approach to primary retroperitoneal pathologies: what the radiologist needs to know

Retroperitoneal soft tissue lesions represent a wide range of disease processes with overlapping imaging findings. Familiarity with the CT and MR characteristics of these conditions is important to guide clinical evaluation. We review the tissue types, characteristic clinical, demographic, and imaging features of retroperitoneal tumors and tumor-like non-neoplastic conditions with CT and MR correlation, including anatomic and imaging clues, and provide a diagnostic approach to aide the radiologist in making a specific diagnosis.

Retroperitoneal Liposarcoma with Multilocular Cysts

In this study, we describe a 60-year-old man with a giant retroperitoneal liposarcoma with multilocular cysts. He was admitted to our hospital because of a 5-month history of abdominal distention. Abdominal computed tomography revealed a giant lobulated cystic mass occupying the retroperitoneal space that contained partially solid fat components. Magnetic resonance imaging indicated that this complex mass exhibited a low signal intensity on a T1-weighted image, whereas it exhibited a high and focally intermediate signal intensity on a T2-weighted image. This patient was diagnosed with a mucinous type of retroperitoneal sarcoma, which was then resected. During surgery, the tumor was isolated from the retroperitoneum and other organs, but the detachment was required only because of fixation around the left external iliac artery. The histological diagnosis was a well-differentiated liposarcoma with multilocular cysts that contained old bloody, serous, and mucinous fluids, which are a rare phenomenon in liposarcoma. This case indicates that retroperitoneal liposarcoma should also be considered as a differential diagnosis of retroperitoneal cystic mass.

Practical approach to primary retroperitoneal masses in adults

Primary retroperitoneal masses constitute a heterogeneous group of uncommon lesions and represent a challenge due to overlapping imaging findings. Most are malignant lesions. Although they are more prevalent in adults, they can occur at any age. Such lesions are classified as primary when they do not originate from a specific retroperitoneal organ and are divided, according to the image findings, into two major groups: solid and cystic. The clinical findings are nonspecific and vary depending on the location of the lesion in relation to adjacent structures, as well as on its behavior. The main imaging methods used for staging and surgical planning, as well as for selecting the biopsy site and guiding the biopsy procedure, are computed tomography and magnetic resonance imaging. In most cases, the treatment is challenging, because of the size of the lesions, vascular involvement, or involvement of adjacent organs. In this article, we present a review of the retroperitoneal anatomy and a practical approach to the main imaging features to be evaluated, with a view to the differential diagnosis, which can guide the clinical management.

Retroperitoneal Leiomyosarcoma From the Radiologic Pathology Archives

Leiomyosarcoma is a malignant neoplasm that shows smooth muscle differentiation. It is the second most common sarcoma to affect the retroperitoneum. Retroperitoneal leiomyosarcomas may grow to large sizes before detection and may be an incidental finding at imaging. When symptomatic, retroperitoneal leiomyosarcoma may cause compressive symptoms, including pain. Retroperitoneal leiomyosarcoma most commonly manifests as a large soft-tissue mass, with areas of necrosis. The most frequent pattern of growth is an entirely extravascular mass. Less commonly, leiomyosarcoma may demonstrate both extravascular and intravascular components. Rarely, retroperitoneal leiomyosarcomas are completely intravascular, typically arising from the inferior vena cava. Given its variable imaging features, a large variety of neoplastic and nonneoplastic conditions are included in the differential diagnosis of retroperitoneal leiomyosarcoma. In this review, the authors discuss retroperitoneal leiomyosarcoma, with emphasis on the pathologic basis of disease, and illustrate the multimodality imaging appearances of retroperitoneal leiomyosarcoma using cases from the Radiologic Pathology Archives of the American Institute for Radiologic Pathology. The authors review important differential considerations of retroperitoneal leiomyosarcoma, focusing on the extravascular pattern of growth, and emphasize clinical and imaging features that help radiologists differentiate leiomyosarcoma from the most frequent mimics. The information presented in this review will aid radiologists in fulfilling their key roles in the diagnosis, operative planning, and follow-up of patients with retroperitoneal leiomyosarcoma.

MR imaging features of benign retroperitoneal paragangliomas and schwannomas

Background

To determine whether MRI feature analysis can differentiate benign retroperitoneal extra-adrenal paragangliomas and schwannomas.

Methods

The MRI features of 50 patients with confirmed benign retroperitoneal extra-adrenal paragangliomas and schwannomas were retrospectively reviewed by two radiologists blinded to the histopathologic diagnosis. These features were compared between two types of tumours by use of the Mann-Whitney test and binary logistic regression. The patients’ clinical characteristics were reviewed.

Results

Analysis of MRI images from 50 patients revealed no significant differences in the quantitative MRI features of lesion size, ratio of diameter and apparent diffusion coefficient. There were significant differences in the qualitative MRI features of location, necrosis, cysts and degree of tumour enhancement for two readers, with no significant differences in the other qualitative MRI features between these tumours. The combination of necrosis with degree of tumour enhancement during the arterial phase increased the probability that a retroperitoneal mass would represent retroperitoneal extra-adrenal paraganglioma as opposed to schwannoma.

Conclusion

We have presented the largest series of MRI features of both benign retroperitoneal extra-adrenal paragangliomas and schwannomas. Some MRI features assist in the differentiation between these tumours, with imaging features consisting of necrosis and avid enhancement during the arterial phase, suggestive of retroperitoneal extra-adrenal paragangliomas.

MR imaging features of benign retroperitoneal extra-adrenal paragangliomas

The goal of this study was to retrospectively review the magnetic resonance imaging (MRI) features of retroperitoneal extra-adrenal paragangliomas and to evaluate the diagnostic capabilities of MRI. Twenty-four patients with confirmed benign retroperitoneal extra-adrenal paragangliomas who underwent preoperative MRI and surgical resection were enrolled. The patients’ clinical characteristics and MRI features were reviewed by two radiologists. There were no significant differences in the qualitative and quantitative MRI features were determined by the reviewers. High signal intensity in T2-weighted imaging (T2WI) and diffusion-weighted imaging (DWI) was observed in all tumors. In contrast T1-weighted imaging (T1WI) in the arterial phase, 83.33% of the tumors were clearly enhanced. In 87.5% of cases, a persistent enhancement pattern was observed in the venous and delayed phases, and 12.5% of tumors showed a “washout” pattern. The tumor capsule, intratumoral septum and degenerations were visualized in the tumors and may be helpful in the qualitative diagnosis of extra-adrenal paragangliomas in MRI. MRI was useful in locating the position, determining the tumor ranges and visualizing the relationship between the tumors and adjacent structures. The presence of typical clinical symptoms and positivity of biochemical tests are also important factors in making an accurate preoperative diagnosis.

Differentiation of Lymphoma Presenting as Retroperitoneal Mass and Retroperitoneal Fibrosis: Evaluation with Multidetector-row Computed Tomography

Background:

Retroperitoneal fibrosis (RPF) and lymphoma presenting as retroperitoneal mass may closely resemble each other and misdiagnosis may occur. This study investigated the differential imaging features of RPF and lymphoma which presented as a retroperitoneal soft tissue using multidetector-row computed tomography (MDCT).

Methods:

The 42 consecutive patients were included in this retrospective review, including 19 RPF patients (45.2%; including 13 males and 6 females; mean age: 56.7 ± 6.2 years) and 23 patients with lymphoma (54.8%; including 14 males and 9 females; mean age: 57.4 ± 12.3 years). An array of qualitative computed tomography (CT) features of lesions in 42 consecutive patients with newly diagnosed untreated RPF and lymphoma were retrospectively analyzed. The quantitative size of the lesion at the para-aortic region and attenuation in the precontrast, arterial, and portal phases were calculated in regions of interest and compared between the patients with newly diagnosed untreated RPF and with lymphoma. Receiver operating characteristic curve analysis was used to assess the potential diagnostic value of each quantitative parameter. Inter-reader concordance was also calculated.

Results:

Mean ages between patients with RPF and lymphoma were not significantly different (56.7 ± 6.2 years vs. 57.4 ± 12.3 years P = 0.595). Compared to those in patients with lymphoma, homogeneous enhancement (65.2% vs. 94.7%, P = 0.027) and pelvic extension (52.2% vs. 89.5%, P = 0.017) were significantly more common while the involvement of additional nodes (78.3% vs. 5.3%, P < 0.001), suprarenal extension (60.9% vs. 15.8%, P = 0.004), and aortic displacement (43.5% vs. 5.3%, P = 0.006) were significantly less common in patients with RPF. Lesion size at the para-aorta was significantly greater in patients with lymphoma, compared with RPF patients (3.9 ± 1.2 cm vs. 1.8 ± 0.6 cm; P < 0.001). The attenuation values in three phases were not significantly different between patients with RPF and lymphoma. Inter-reader concordance for subjective features ranged from very good to excellent (range: 85.7–100.0%).

Conclusions:

This study showed that MDCT can help differentiate between untreated RPF and lymphoma on the basis of qualitative CT features and lesion sizes. Differentiating RPF from lymphoma on the basis of attenuation values in the precontrast, arterial, and portal phases was difficult to accomplish.

Primary retroperitoneal masses: what is the differential diagnosis?

Primary retroperitoneal masses include a diverse, and often rare, group of neoplastic and non-neoplastic entities that arise within the retroperitoneum but do not originate from any retroperitoneal organ. Their overlapping appearances on cross-sectional imaging may pose a diagnostic challenge to the radiologist; familiarity with characteristic imaging features, together with relevant clinical information, helps to narrow the differential diagnosis. In this article, a systematic approach to identifying and classifying primary retroperitoneal masses is described. The normal anatomy of the retroperitoneum is reviewed with an emphasis on fascial planes, retroperitoneal compartments, and their contents using cross-sectional imaging. Specific radiologic signs to accurately identify an intra-abdominal mass as primary retroperitoneal are presented, first by confirming the location as retroperitoneal and secondly by excluding an organ of origin. A differential diagnosis based on a predominantly solid or cystic appearance, including neoplastic and non-neoplastic entities, is elaborated. Finally, key diagnostic clues based on characteristic imaging findings are described, which help to narrow the differential diagnosis. This article provides a comprehensive overview of the cross-sectional imaging features of primary retroperitoneal masses, including normal retroperitoneal anatomy, radiologic signs of retroperitoneal masses and the differential diagnosis of solid and cystic, neoplastic and non-neoplastic retroperitoneal masses, with a view to assist the radiologist in narrowing the differential diagnosis.

Retroperitoneal low-flow vascular malformations: characteristic MRI findings correlated with histopathological findings

PURPOSE

To evaluate the MRI findings of retroperitoneal low-flow vascular malformations (RLVMs) correlated with histopathological findings.

METHODS

Two radiologists reviewed the MRI findings of 4 RLVMs (3 with capillary malformations and 1 with a venous malformation). First, they evaluated the visibility, signal intensities, and signal homogeneity of each lesion on non-fat-suppressed breath-hold T2-weighted single-shot fast spin-echo (non-FS SSFSE) images and fat-suppressed T2-weighted fast spin-echo (FS T2-weighted FSE) images. Second, the kinetic patterns and the internal enhancement patterns were analyzed for each lesion on multi-phasic contrast-enhanced (CE) images. After these image analyses, the MRI findings were correlated with the histopathological findings.

RESULT

Histopathologically, the 4 RLVMs did not exhibit remarkable degeneration and were present in the retroperitoneal fat tissue without clear capsules. On the non-FS SSFSE images, 3 of the 4 RLVMs could not be discriminated from the surrounding retroperitoneal fat tissue (invisible), and the remaining lesion was barely visible with an indistinct margin. On the FS T2-weighted FSE images, however, all the RLVMs were clearly visualized as homogeneous high-signal intensities. On the multi-phasic CE images, all the capillary malformations exhibited fast enhancement, while a venous malformation showed slow enhancement. Furthermore, the RLVMs tended to exhibit a centripetal filling pattern.

CONCLUSION

The RLVMs blended in with the surrounding retroperitoneal fat tissue on non-FS SSFSE images, like phantoms, whereas they were clearly visualized on FS T2-weighted FSE images. On multi-phasic CE images, the RLVMs tended to exhibit a centripetal filling pattern. These imaging features may be useful diagnostic clues for RLVMs.

Retroperitoneal tumors in the pelvis: a diagnostic challenge in gynecology

Retroperitoneal tumors can pose a diagnostic and therapeutic challenge to gynecologists because of their rarity, late presentation, and complex anatomical location in the retroperitoneum. This article reviews the diagnosis and management of retroperitoneal tumors in the pelvis, and highlights the potential pitfalls that may be faced by gynecologists.

A comprehensive review of the retroperitoneal anatomy, neoplasms, and pattern of disease spread

A clear understanding of the normal anatomy and pattern of disease spread is important in evaluating many retroperitoneal disorders. Primary retroperitoneal tumors are uncommon, accounting for 0.1%-0.2% of all malignancies in the body; 80%-90% of all primary retroperitoneal tumors are malignant. The primary retroperitoneal neoplasms can be divided into solid or cystic masses. The solid neoplasms can be classified according to their tissue of origin into 3 main categories: mesodermal tumors, neurogenic tumors, and extragonadal germ cell tumors. Computed tomography and magnetic resonance imaging play a vital role in the localization, characterization, evaluation of the extent of local invasion, assessment of metastases, and determination of treatment response for these tumors. The diagnosis of a primary retroperitoneal malignancy is often challenging owing to overlap of imaging findings. A definitive diagnosis can be established only at histopathologic analysis. However, knowledge of the important tumor characteristics, growth pattern, and vascularity can assist in narrowing the differential diagnosis.

Imaging of the retroperitoneum

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. This article discusses clinically relevant anatomy of the abdominal retroperitoneal spaces, their cross-sectional imaging evaluation with computed tomography and magnetic resonance imaging, and the imaging features of common retroperitoneal pathologic processes.

Imaging of uncommon retroperitoneal masses

Retroperitoneal masses not arising from major solid organs are uncommon. Although there is no simple method of classifying retroperitoneal masses, a reasonable approach is to consider the masses as predominantly solid or cystic and to subdivide these into neoplastic and nonneoplastic masses. Because the treatment options vary, it is useful to be able to differentiate these masses by using imaging criteria. Although the differential diagnosis of retroperitoneal masses can be narrowed down to a certain extent on the basis of imaging characteristics, patterns of involvement, and demographics, there is still a considerable overlap of imaging findings for these masses, and histologic examination is often required for definitive diagnosis. Computed tomography (CT) and magnetic resonance (MR) imaging play an important role in characterization and in the assessment of the extent of the disease and involvement of adjacent and distant structures. Familiarity with the CT and MR imaging features of various retroperitoneal masses will facilitate accurate diagnosis and staging for aggressive lesions.

Retroperitoneal fibrosis as a cause of positive FDG PET/CT

This article educates the reader on idiopathic retroperitoneal fibrosis and emphasizes the importance of considering conditions that mimic this disease on PET/CT through an illustrative case of a 58 year-old man presenting with intermittent abdominal, back, and scrotal pain undergoing successive PET/CT scans, both for diagnosis and following treatment.

Pseudocyst formation in retroperitoneal fibrosis relapse

We describe a 45-year-old male patient with recurrent retroperitoneal fibrosis (RPF), in whom a pseudocyst in the peri-aortic fibrotic mantle was diagnosed. Without any intervention other than oral treatment with tamoxifen, the pseudocyst showed significant regression. Although rare, pseudocyst formation may sometimes appear in RPF and may mimic other benign and malignant conditions. This is the first paper to describe pseudocyst formation in an RPF relapse.

[Cystic lymphangioma: an unusual cause of lower limb lymphedema]

We report an unusual cause of unilateral lymphedema of the right limb rapidly increasing in a young woman. Ultrasonography ruled out the diagnosis of iliac deep venous thrombosis or extrinsic compression: the B mode scan revealed a mass located below the aortic bifurcation and along the iliac vessels, without any compressive effect. The lesion was heterogeneous associating both tissular and cystic aspects. The lower limb lymphoscintigraphy showed an interruption of the colloid circulation at the right iliac level. Computed tomography did not give any additional information. Magnetic resonance imaging before then after gadolinium showed typical aspects of cystic lymphangioma and confirmed the ultrasonography hypothesis. Considering that this tumor is benign, that surgery would be difficult because of the anatomic situation of the mass, and that post-operative involution of the edema is uncertain, the treatment was based on compressive stockings and regular follow up.