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Everything you need to know about Computed Tomography (CT) & CT Scanning

Musculoskeletal: Retroperitoneum Imaging Pearls - Educational Tools | CT Scanning | CT Imaging | CT Scan Protocols - CTisus
Imaging Pearls ❯ Musculoskeletal ❯ Retroperitoneum

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  • “Myxoid liposarcomas are often predominantly nonfatty, with a cystic appearance at CT and MRI due to the extracellular myxoid matrix (hypoattenuating compared with muscle at CT, high signal intensity at T2-weighted MRI, and low signal intensity at T1-weighted MRI). However, unlike cystic lesions, myxoid liposarcomas demonstrate varying amounts of contrast material enhancement. While they generally contain a paucity of fat, the presence of a small amount of fat in lacy septa or nodular components is pathognomonic for myxoid liposarcomas.”
    Radiologic-Pathologic Correlation of Primary Retroperitoneal Neoplasms
    Khalid Al-Dasuqi et al.
    RadioGraphics 2020; 40:1631–1657
  • “At CT, lymphatic malformations often appear as a uniformly cystic mass and exhibit attenuation that is near that of water. The walls and/or septa are rarely perceptible, and septal enhancement is difficult to appreciate at CT. They classically can involve more than one retroperitoneal compartment and can appear as an elongated and insinuating mass, which is an important imaging clue.”
    Radiologic-Pathologic Correlation of Primary Retroperitoneal Neoplasms
    Khalid Al-Dasuqi et al.
    RadioGraphics 2020; 40:1631–1657
  • “A large non–fat-containing retroperitoneal mass with involvement of a contiguous vessel and varying internal necrosis should raise the possibility of a leiomyosarcoma.”
    Radiologic-Pathologic Correlation of Primary Retroperitoneal Neoplasms
    Khalid Al-Dasuqi et al.
    RadioGraphics 2020; 40:1631–1657
  • “Liposarcoma is a malignant adipose tissue tumor. It accounts for approximately 15% of all soft-tissue tumors, with 10%–20% of liposarcomas arising in the retroperitoneum. Liposarcoma is the most common primary retroperitoneal sarcoma, accounting for 35% of all malignant retroperitoneal soft-tissue tumors in adult patients. They often manifest as large encapsulated fat-containing masses that displace adjacent structures, and average patients typically present during their fifth through seventh decades of life.”
    Radiologic-Pathologic Correlation of Primary Retroperitoneal Neoplasms
    Khalid Al-Dasuqi et al.
    RadioGraphics 2020; 40:1631–1657
  • “Liposarcomas are histologically divided into four subtypes including (a) well-differentiated liposarcoma (also called atypical lipomatous tumor when found in the extremities), (b) myxoid liposarcoma, (c) pleomorphic liposarcoma, and (d) dedifferentiated liposarcoma (9). Among these, well-differentiated liposarcomas are the most common, followed by the dedifferentiated subtype, with myxoid and pleomorphic liposarcomas rarely seen in the retroperitoneum. In one study  of 177 patients with retroperitoneal liposarcomas, well-differentiated tumors were found in 56% of patients, while dedifferentiated lesions were present in 37% of patients.”
    Radiologic-Pathologic Correlation of Primary Retroperitoneal Neoplasms
    Khalid Al-Dasuqi et al.
    RadioGraphics 2020; 40:1631–1657
  • “Leiomyosarcoma is a malignant tumor of smooth muscle cells, with a retroperitoneal location in 12%–69% of cases. It is the second most common primary malignant retroperitoneal sarcoma, accounting for 28% of cases. Leiomyosarcomas are typically diagnosed during the fifth to sixth decades of life, more often in women than in men. Leiomyosarcoma is believed to originate from the large blood vessels in the retroperitoneum (eg, the inferior vena cava) and/or their tributaries . Nevertheless, leiomyosarcomas most commonly manifest as extravascular tumors (62% of cases) and are rarely completely intravascular (5%). In 33% of cases, leiomyosarcomas have both an intravascular and an extravascular component .”
    Radiologic-Pathologic Correlation of Primary Retroperitoneal Neoplasms
    Khalid Al-Dasuqi et al.
    RadioGraphics 2020; 40:1631–1657
  • “Similar to liposarcomas, leiomyosarcomas are often large when patients present, and symptoms are usually related to compression of adjacent structures. Metastases are seen at the time of diagnosis in 9% of patients with extravascular tumors and 23% of patients with intravascular tumors, with the lungs, liver, and peritoneum being the most common sites. Prognosis is typically dependent on achieving complete excision with wide negative margins .”
    Radiologic-Pathologic Correlation of Primary Retroperitoneal Neoplasms
    Khalid Al-Dasuqi et al.
    RadioGraphics 2020; 40:1631–1657
  • “Leiomyosarcomas usually manifest as large soft-tissue masses, with internal heterogeneity and heterogeneous enhancement usually secondary to necrosis and hemorrhage. The mean tumor size for lesions with and without vascular involvement has been reported as 10.4 cm and 11.3 cm, respectively . Calcifications are not commonly found, and adipose tissue is absent . Purely intravascular lesions appear as heterogeneously enhancing expansile masses.”
    Radiologic-Pathologic Correlation of Primary Retroperitoneal Neoplasms
    Khalid Al-Dasuqi et al.
    RadioGraphics 2020; 40:1631–1657
  • “Solitary fibrous tumors, previously known as localized mesothelioma, are rare mesenchymal tumors that arise from fibroblast-like cells in the connective tissue. They are on the same spectrum of tumors as hemangiopericytomas, and the two terms are often used interchangeably. Approximately one-third of solitary fibrous tumors are intraabdominal, and the most common intraabdominal site is the retroperitoneum. The majority of patients are diagnosed in the fifth to seventh decades of life, but the tumor can arise at any age. Most solitary fibrous tumors are benign, with an estimated malignancy rate of 20%–40%. Retroperitoneal solitary fibrous tumors are usually initially asymptomatic and can grow large before causing symptoms.”
    Radiologic-Pathologic Correlation of Primary Retroperitoneal Neoplasms
    Khalid Al-Dasuqi et al.
    RadioGraphics 2020; 40:1631–1657
  • “Schwannomas, also known as neurolemmas, are another type of benign nerve sheath tumor that account for 4% of all retroperitoneal tumors. As opposed to neurofibromas, they are exclusively made of benign neoplastic Schwann cells and are separable from the nerve fibers. Thus, they tend to grow eccentrically from peripheral nerve fibers. Schwannomas can occur at any age but are more common between the second and fifth decades of life. Most cases are sporadic, with the exception of a small fraction of cases that can be associated with neurofibromatosis type 2. Malignant degeneration is rare in schwannomas.”
    Radiologic-Pathologic Correlation of Primary Retroperitoneal Neoplasms
    Khalid Al-Dasuqi et al.
    RadioGraphics 2020; 40:1631–1657
  • “Schwannomas are often indistinguishable from neurofibromas at imaging. They often appear as round or fusiform hypoattenuating masses at CT. The typical signal intensity characteristics of schwannomas at MRI are similar to those of neurofibromas, with intermediate signal intensity at T1-weighted MRI (iso- to hypointense to muscle) and signal hyperintensity at T2-weighted MRI. Variable enhancement is seen at CT and MRI. In addition, schwannomas can show the target sign, although it is seen less frequently compared with neurofibromas.”
    Radiologic-Pathologic Correlation of Primary Retroperitoneal Neoplasms
    Khalid Al-Dasuqi et al.
    RadioGraphics 2020; 40:1631–1657
  • “Malignant peripheral nerve sheath tumors (MPNSTs) are malignant soft-tissue sarcomas that arise from peripheral nerves either de novo (approximately 50%) or in a preexisting plexiform neurofibroma. They account for up to 10% of soft-tissue sarcomas. The age at onset in patients with neurofibromatosis type 1 is typically 20–30 years, and patients without neurofibromatosis type 1 tend to be older than 60 years at diagnosis. A small subset of MPNSTs occur in patients who have undergone prior radiation therapy (often for breast cancer or lymphoma), with an average lag time of 15 years. Presenting symptoms are usually related to the nerve or nerves involved and are similar to symptoms of neurofibroma. A sudden increase in size of a known neurofibroma is also suggestive of an MPNST . Long-term prognosis is poor because of the potential of local recurrence and metastasis.”
    Radiologic-Pathologic Correlation of Primary Retroperitoneal Neoplasms
    Khalid Al-Dasuqi et al.
    RadioGraphics 2020; 40:1631–1657
  • “Paragangliomas, also known as extra-adrenal pheochromocytomas, are rare tumors of chromaffin cell origin that arise from the extra-adrenal paraganglion cells in the sympathetic or parasympathetic chains. Sympathetic paragangliomas secrete catecholamine, and approximately 40% of patients with them present with clinical findings related to excess catecholamine, including hypertension and tachycardia. Parasympathetic paragangliomas are located in the base of the skull and neck and are associated with the branches of the glossopharyngeal and vagal nerves, whereas sympathetic paragangliomas arise anywhere along the sympathetic chain, most commonly in the abdomen (approximately 75% of all sympathetic paragangliomas). Therefore, retroperitoneal paragangliomas are almost exclusively sympathetic paragangliomas . In the abdomen, the most common location for primary paragangliomas is in the organ of Zuckerkandl, which is located at the origin of the inferior mesenteric artery near the aortic bifurcation.”
    Radiologic-Pathologic Correlation of Primary Retroperitoneal Neoplasms
    Khalid Al-Dasuqi et al.
    RadioGraphics 2020; 40:1631–1657
  • “Paragangliomas are associated with several genetic disorders in approximately 30%–40% of cases, including multiple endocrine neoplasia syndromes and von Hippel–Lindau syndrome . The mean age at presentation of patients with paraganglioma is during the second to fourth decades of life. The diagnosis can be made clinically on the basis of detection of elevated metanephrine or vanillylmandelic acid levels in the urine. The risk of malignancy in sympathetic paragangliomas is estimated to be in the range of 30%–40%. Treatment usually consists of surgical resection with postoperative radiation.”
    Radiologic-Pathologic Correlation of Primary Retroperitoneal Neoplasms
    Khalid Al-Dasuqi et al.
    RadioGraphics 2020; 40:1631–1657
  • “Benign and malignant paragangliomas are difficult to distinguish on the basis of imaging unless tumors appear locally aggressive or metastases are present at the time of diagnosis. At CT, paragangliomas are typically heterogeneous, and necrosis, hemorrhage, and/or calcifications can often be seen. Avid contrast material enhancement is often noted because of hypervascularity, especially peripherally. Early concerns about the risk of a hypertensive crisis after the use of intravenous contrast material in patients with known catecholamine hypersecreting tumors have since been refuted in subsequent studies.”
    Radiologic-Pathologic Correlation of Primary Retroperitoneal Neoplasms
    Khalid Al-Dasuqi et al.
    RadioGraphics 2020; 40:1631–1657
  • “Lymphatic malformation (also known as cystic lymphangioma), is a benign cystic mass comprising dilated lymphatic channels, which forms secondary to failure of normal lymphatic channel communication or drainage. They are considered a form of slow-flowing vascular malformation. Lymphatic malformations can occur in patients of any age, but most of them manifest in early childhood. They are most commonly found in the head or neck and are rarely encountered in the abdomen. They can be asymptomatic or may be associated with vague abdominal discomfort.”
    Radiologic-Pathologic Correlation of Primary Retroperitoneal Neoplasms
    Khalid Al-Dasuqi et al.
    RadioGraphics 2020; 40:1631–1657
  • “Because most lymphatic malformations manifest in patients during childhood, initial imaging assessment is often performed with US, which often shows a multiloculated anechoic mass with thin septa. Vascularity can occasionally be seen in the septa. At CT, lymphatic malformations often appear as a uniformly cystic mass and exhibit attenuation that is near that of water. The walls and/or septa are rarely perceptible, and septal enhancement is difficult to appreciate at CT. They classically can involve more than one retroperitoneal compartment and can appear as an elongated and insinuating mass, which is an important imaging clue .”
    Radiologic-Pathologic Correlation of Primary Retroperitoneal Neoplasms
    Khalid Al-Dasuqi et al.
    RadioGraphics 2020; 40:1631–1657
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