INTRODUCTION

Liposarcoma is a malignant tumor of adipose tissue and is the most common primary retroperitoneal sarcoma. Liposarcomas can be histologically divided into four subtypes including well-differentiated liposarcoma, myxoid liposarcoma, pleomorphic liposarcoma, and dedifferentiated liposarcoma.[1] The most common of these seen in the retroperitoneum are well-differentiated liposarcoma and dedifferentiated liposarcoma. Dedifferentiation liposarcomas are high-grade sarcomas and are more clinically aggressive than the well-differentiated subtype.[2] Cystic change in dedifferentiated liposarcoma is a very rare phenomenon. To date, only a few cases of cystic retroperitoneal dedifferentiated liposarcomas have been reported.[3-5] Herein, we describe a case of cystic retroperitoneal dedifferentiated liposarcoma complicated by hemorrhage.

CASE REPORT

An 86-year-old male presented to the emergency department complaining of acute shortness of breath as well as background unexplained weight loss over several months. The patient also reported recent high-impact falls which led to a right femoral subcapital fracture that was treated by right hip hemiarthroplasty in the preceding few months. Clinical assessment revealed peripheral edema and hypoxia but no fever, night sweats, or constitutional symptoms. Laboratory assessment showed increased serum alkaline phosphatase and D-dimer levels. While hemoglobin has been chronically low for months, there was no acute decline to suggest recent hemorrhage. The remaining blood work including white cell count, neutrophil count, and C-reactive protein was normal. The initial chest radiograph was unremarkable.

A contrast-enhanced computed tomography (CT) scan of the abdomen and pelvis was obtained which showed a large heterogeneous complex cystic hypoenhancing lesion in the left retroperitoneum posterior to the left kidney measuring 13 × 12 × 24 cm and demonstrating mixed density of 9–32 Hounsfield units [Figure 1]. The mass displaces the left kidney and encases the left renal vasculature and collecting system at the hilum leading to mild hydronephrosis. While the appearance of the mass is non-specific on CT, given the recent history of multiple falls, a complicated chronic hematoma was considered in the differential at the time. Subsequent magnetic resonance imaging (MRI) demonstrates heterogeneous T2-weighted hyperintensity suggestive of multi-cystic areas within the mass [Figure 2]. Multiple areas of T1-weighted hyperintensity are also seen on the T1 fat saturated sequence suggestive of hemorrhagic content [Figure 2]. Chemical shift T1 imaging [Figure 3] demonstrates associated microscopic lipid content as denoted by signal loss on the out-of-phase image compared to the in-phase image in the superior cystic component of the mass [Figures 3a and 3b]. There is diffusion restriction in the periphery of the solid components of the mass [Figure 3d]. The solid components show avid enhancement in the post-contrast fat saturated T1 [Figure 4].

Figure 1:: An 86-year-old male with cystic retroperitoneal dedifferentiated liposarcoma who presented with unexplained weight loss and frequent falls. Axial (a), Coronal (b), and Sagittal (c) contrast enhanced computed tomography (CT) images of the abdomen and pelvis in the portal phase demonstrate a large heterogenous complex cystic lesion in the left retroperitoneum (arrows). Differential considerations on CT included a complex hematoma, abscess, or a cystic tumor.

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Figure 2:: An 86-year-old male with cystic retroperitoneal dedifferentiated liposarcoma who presented with unexplained weight loss and frequent falls. Axial T2 (a), Axial T1 (b), Coronal T2 (c), and Coronal fatsaturated T1 (d) Images demonstrate heterogeneous mixed T2 signal intensity with foci of T2 high signal intensity throughout the lesion consistent with cystic components (white arrows). Multiple areas of T1 high signal suggesting hemorrhage of different ages (red arrows).

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Figure 3:: An 86-year-old male with cystic retroperitoneal dedifferentiated liposarcoma who presented with unexplained weight loss and frequent falls. T1 in-phase (a) and T1 out-of-phase (b) images as well as diffusion-weighted imaging (c) and apparent diffusion coefficient map (d) demonstrate foci of microscopic fat in the superior portion of the retroperitoneal mixed cystic mass (white arrow), and restricted diffusion in the periphery of the retroperitoneal heterogenous mixed cystic mass (red arrows).

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Figure 4:: An 86-year-old male with cystic retroperitoneal dedifferentiated liposarcoma who presented with unexplained weight loss and frequent falls. Post contrast axial fat saturated T1 (a) and subtraction (b) as well as post contrast coronal fat saturated T1 (c) and subtraction (d) images demonstrate enhancement of the thick irregular peripheral walls of the mass and its thick internal septations (white arrows). No enhancement of the predominantly central cystic components (asterisk).

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The findings on CT and MRI are most consistent with a large left retroperitoneal cystic neoplasm with internal hemorrhage of differing ages. Given the signal loss seen on the out-of-phase image [Figure 3b arrow], the first differential diagnosis considered is liposarcoma, followed by lymphoma or peripheral nerve sheath tumor. The patients underwent ultrasound-guided biopsy with subsequent pathology confirming a diagnosis of cystic retroperitoneal dedifferentiated liposarcoma. Given the advanced age and frailty of the patient, further management of this mass was not pursued.

DISCUSSION

Retroperitoneal sarcoma is rare with a mean incidence of 2.7/million though accounts for approximately 12–15% of all soft-tissue sarcomas.[6] They are frequently incidental findings on imaging for non-related symptoms or diseases. Liposarcoma is the most common primary retroperitoneal sarcoma with well-differentiated and dedifferentiated liposarcoma being the two predominant subtypes.[1] Dedifferentiated liposarcoma is a high-grade sarcoma demonstrating more aggressive behavior compared to well-differentiated liposarcoma with the propensity for local recurrence and metastasis.[2] The characteristic imaging appearance of dedifferentiated liposarcoma is a mass with coexisting fatty and non-fatty tissue, often by a focal nodular non-lipomatous component >1 cm in size. Calcifications can be seen and are a sign of poor prognosis.[7]

Predominant cystic change is uncommon in retroperitoneal liposarcoma; hence, radiologists may not consider primary cystic retroperitoneal liposarcoma in the differential diagnosis. To date, only a few case reports of predominantly cystic retroperitoneal liposarcoma have been published in the literature. In a 2017 report by Uchihashi et al., the authors described an elderly female who presented with a large cystic dedifferentiated liposarcoma without a solid component.[3] An additional case of cystic dedifferentiated liposarcoma was previously described by Khoury et al. in the setting of prior chemoradiation therapy.[4] The radiologic diagnosis of our case was difficult due to its large cystic component and non-specific appearance on CT. Given the patient history of frequent falls leading to recent right total hip arthroplasty, the heterogeneous appearance of the mass on CT makes hematoma a plausible differential diagnosis on the initial CT examination. The diagnosis of primary retroperitoneal neoplasm and more specifically liposarcoma was only made possible following MRI characterization.

Dedifferentiated liposarcomas represents the conversion of well-differentiated components to non-fat-derived tumor components and requires both lipogenic well-differentiated liposarcoma and cellular non-lipogenic sarcoma. However, well-differentiated and dedifferentiated liposarcomas share similar underlying genetic and histological characteristics including common genetic abnormalities with amplified sequences arising from the long arm of chromosome 12 (12q13-15), which includes amplifications of CDK4 and MDM2 cell cycle oncogenes.[8] These genetic and histological similarities contribute to a challenge in morphological differentiation of these tumors on imaging. The previous studies have investigated imaging features such as morphology of fat and non-fat components in liposarcomas. As shown in [Table 1], Rajiah et al. summarized the imaging features of different retroperitoneal masses.[9] Other imaging features described in both atypical lipomatous tumor/ well-differentiated liposarcoma includes large size of the lesion (more than 10 cm), thick irregular/nodular septa, non-adipose areas or nodules, and fat content involving <75% of the lesion. Other described imaging characteristics for distinguishing between well-differentiated and dedifferentiated liposarcomas include prominent foci of high signal on fluid sensitive sequences and septal enhancement, although these features are shown to have limited specificities.[10] To date, no combinations of imaging features are known to reliably differentiate between these lesions with definitive subtype diagnosis often requiring histological analysis following biopsy of the most suspicious portions of the lesion or even tumor resection.

Table 1:: Imaging features suggestive of a specific diagnosis for retroperitoneal masses.

Imaging feature Diagnosis Pure fat-containing mass Lipoma, well-differentiated liposarcoma Heterogenous mass with fat Dedifferentiated liposarcoma, myelolipoma, angiomyolipoma Fat-fluid level Teratoma, well-differentiated liposarcoma Fat with calcification, teeth, or fluid Teratoma Myxoid stroma Myxoid liposarcoma, neurogenic tumor, myxoid malignant fibrous histiocytoma. Less common diagnosis: desmoid tumor, hemangiopericytoma, leiomyoma or leiomyosarcoma, rhabdomyosarcoma, malignant mesenchymoma. Large mass, extensive necrosis, invasion of IVC Leiomyosarcoma Fluid-fluid level caused by hemorrhage Paraganglioma Extremely hypervascular Paraganglioma, hemangiopericytoma Moderately hypervascular Myxoid malignant fibrous histiocytoma, leiomyosarcoma, other sarcoma Hypovacular Lymphoma, low-grade liposarcoma, benign tumor T2 hypointenisty Lymphoma, desmoid tumor, small round cell tumor, retroperitoneal fibrosis, Erdheim-Chester disease Paravertebral mass Neurogenic tumor Paravertebral mass, high catecholamine levels, hypertension Paraganglioma Extension between normal structures, encasement without luminal compression lymphangioma, ganglioneuroma, lymphoma (gloating aorta or CT angiogram sign) Extension along normal structures Paraganglioma, ganglioneuroma Mantlelike mass around aorta of IVC Lymphoma, retroperitoneal fibrosis, Erdheim-Chester disease floating aorta or CT angiogram sign Lymphoma Soft-tissue mass with calcification Malignant fibrous histiocytoma, teratoma, extraosseous chondrosarcoma/Ewing sarcoma, synovial sarcoma, dedifferentiated liposarcoma Cystic mass with solid tumor enhancement Myxoid liposarcoma, schwannoma, neurofibroma Cystic mass with slow, progressive enhancement Lymphangioleiomyoma, urinoma Cystic mass with pulmonary cysts Lymphangioleiomyoma Cyst after trauma With high attenuation or intensity Hematoma With obstruction Urinoma Cyst wit negative attenuation, history of radical lymphadenectomy Lymphocele Multilocular cystic mass, calcification, elongated shape, crossing retroperitoneal compartments lymphangioma Cystic mass, calcification, no contrast enhancement, bone lesions, visceral involvement Lymphangiomatosis Cyst, history of pancreatitis, high amylase level Pancreatic pseudocyst Cyst in obese woman receiving hormonal therapy for menstrual irregularity Mullerican cyst Unilocular cyst in subdiaphragmatic space Bronchogenic cyst Multilocular cyst, thick septa, calcification, right lower quadrant Pseudomyxoma retroperitoneal Presacral unilocular cyst Epidermoid cyst Presacral multilocular cyst Tailgut cyst Multilocular perianal cyst with history of anal fistual Perianal mucinous carcinoma

Surgical resection remains the mainstay of curative therapy. Neoadjuvant or adjuvant chemotherapy could be considered in patients with large tumors (>5 cm) or high-grade round cell or pleomorphic subtypes. Neoadjuvant or adjuvant radiation therapy may be used for local control in large high-grade liposarcoma.[2]

CONCLUSION

We have presented an uncommon case of a predominantly cystic retroperitoneal dedifferentiated liposarcoma. While liposarcoma is the most common primary retroperitoneal neoplasm, occurring in 33% of cases, they are most typically solid. Predominant cystic change is unusual in retroperitoneal liposarcoma; hence, why radiologists may not consider primary cystic retroperitoneal liposarcoma in the differential diagnosis of these retroperitoneal lesions. To date, only a few case reports of cystic retroperitoneal liposarcoma have been published in the literature. The diagnosis of primary retroperitoneal neoplasm and more specifically liposarcoma with a predominantly cystic component is only made possible following MRI characterization.