Neoplastic and non-neoplastic proliferative disorders of the perirenal space: cross-sectional imaging findings

Retroperitoneal anatomy with the aid of pathologic fluid: An imaging pictorial review

The retroperitoneum, a complex anatomical space within the abdominopelvic region, encompasses various vital abdominal organs. It is compartmentalized by fascial planes and contains potential spaces critical in multiple disease processes, including inflammatory effusions, hematomas, and neoplastic conditions. A comprehensive understanding of the retroperitoneum and its potential spaces is essential for radiologists in identifying and accurately describing the extent of abdominopelvic disease. This pictorial review aims to describe the anatomy of the retroperitoneum while discussing commonly encountered pathologies within this region. Through a collection of illustrative images, this review will provide radiologists with valuable insights into the retroperitoneum, facilitating their diagnostic proficiency to aid in appropriate patient clinical management.

Perirenal lymphatics: anatomy, pathophysiology, and imaging spectrum of diseases

Despite being rarely discussed, perinephric lymphatics are involved in many pathological and benign processes. The lymphatic system in the kidneys has a harmonious dynamic with ureteral and venous outflow, which can result in pathology when this dynamic is disturbed. Although limited by the small size of lymphatics, multiple established and emerging imaging techniques are available to visualize perinephric lymphatics. Manifestations of perirenal pathology may be in the form of dilation of perirenal lymphatics, as with peripelvic cysts and lymphangiectasia. Lymphatic collections may also occur, either congenital or as a sequela of renal surgery or transplantation. The perirenal lymphatics are also intimately involved in lymphoproliferative disorders, such as lymphoma as well as the malignant spread of disease. Although these pathologic entities often have overlapping imaging features, some have distinguishing characteristics that can suggest the diagnosis when paired with the clinical history.

Review of diagnosis, differential diagnosis, and management of retroperitoneal lymphangioma

Lymphatic malformation (LM) is the currently preferred term for what was previously known as lymphangioma. Retroperitoneal LMs are extremely rare, benign, cystic masses that arise from lymphatic vessels. They can be challenging to diagnose because they resemble other retroperitoneal cystic tumors. The development of treatment strategies for rare diseases, including retroperitoneal LM, requires the acquisition of new knowledge to enhance our understanding of the disease progression. Therefore, we present an update regarding fundamental and advanced issues associated with retroperitoneal LM. This review describes the epidemiology, histopathology, biomedicine, clinical manifestations, radiological features, differential diagnosis, and management of this lesion.

Solid Primary Retroperitoneal Masses in Adults: An Imaging Approach

Mass lesions in the retroperitoneal space may be primary or secondary. Primary retroperitoneal mass lesions are relatively uncommon as compared to pathology that arises secondarily from retroperitoneal organs. These may be solid or cystic lesions. The overlapping imaging features of various solid primary retroperitoneal tumors make the diagnosis difficult, and hence, histopathology remains the mainstay of diagnosis. This paper provides a brief review of the anatomy of the retroperitoneal space and provides an algorithmic approach based on cross-sectional imaging techniques to narrow down the differential diagnosis of solid primary retroperitoneal masses encountered in the adult population.

Solitary Radiolucent Erdheim-chester Disease: A Case Report and Literature Review

Background:

Erdheim-chester disease (ECD) is a rare non-Langerhans histiocytosis of unknown etiology, which typically presents with bilateral symmetric osteosclerosis and multi-organ involvement. Lesions may be intraosseous or extraosseous and involve the heart, pulmonary system, CNS, and skin in order of decreasing likelihood.

Objective:

The objective of this study is to discuss a case of erdheim-chester disease and conduct a review of the literature.

Case:

We describe a rare case of erdheim-chester in an asymptomatic 37-year-old male who was diagnosed after suffering a right ulnar injury. Subsequent evaluation revealed a solitary radiolucent ulnar lesion without multi-system involvement.

Results & Conclusion:

The case is unique in its solitary distribution, lytic radiographic appearance, and asymptomatic presentation preceding pathologic fracture. This presentation may simulate multiple other bone lesions.

Indolent renal involvement with BRAFV600E mutation: Erdheim-Chester, a rare disease with a wide spectrum of clinical manifestations

We present the case of a patient with three-year indolent bilateral ureteral and perirenal masses. Clinical presentation, radiological context, and histopathological findings with detection of BRAF V600E mutation confirmed the diagnosis of Erdheim-Chester disease (ECD). A review of current knowledge regarding diagnosis, clinical assessment, management, and treatment of ECD is also presented.

Imaging Spectrum of Granulomatous Diseases of the Abdomen and Pelvis

A granuloma is a compact organization of mature macrophages that forms because of persistent antigenic stimulation. At the microscopic level, granulomas can undergo various morphologic changes, ranging from necrosis to fibrosis, which along with other specialized immune cells define the appearance of the granulomatous process. Accordingly, the imaging features of granulomatous diseases vary and can overlap with those of other diseases, such as malignancy, and lead to surgical excisions and biopsy. However, given the heterogeneity of granulomas as a disease group, it is often hard to make a diagnosis on the basis of the histopathologic features of granulomatous diseases alone owing to overlapping microscopic features. Instead, a multidisciplinary approach is often helpful. Radiologists need to be familiar with the salient clinical manifestations and imaging findings of granulomatous diseases to generate an appropriate differential diagnosis. ^©RSNA, 2021.

Bilateral Huge Perirenal Angiomyolipoma: Conservative Management of a Time Bomb

Introduction: Bilateral huge perirenal Angiomyolipoma is a very rare entity and has not been reported in the literature to date. The choice of appropriate management for such a rare disease may be a dilemma because each strategy can harbor its own advantages and hazards. Case Presentation: We present our experience with such a patient over seven years of follow-up. Performing surgery in this patient might have ended up in unilateral or bilateral kidney loss, and he refused the surgery and underwent watchful waiting. Conclusions: Like conservative management that was successful for more than seven years. In this case, other treatment options such as angioembolization and surgical resection are vital options with their own risks and benefits.

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.

Pleural effusion and ascites in extrarenal lymphangiectasia caused by post-biopsy hematoma: A case report

BACKGROUND

The renal system has a specific pleural effusion associated with it in the form of “urothorax”, a condition where obstructive uropathy or occlusion of the lymphatic ducts leads to extravasated fluids (urine or lymph) crossing the diaphragm via innate perforations or lymphatic channels. As a rare disorder that may cause pleural effusion, renal lymphangiectasia is a congenital or acquired abnormality of the lymphatic system of the kidneys. As vaguely mentioned in a report from the American Journal of Kidney Diseases, this disorder can be caused by extrinsic compression of the kidney secondary to hemorrhage.

CASE SUMMARY

A 54-year-old man with biopsy-proven acute tubulointerstitial nephropathy experienced bleeding 3 d post hoc, which, upon clinical detection, manifested as a massive perirenal hematoma on computed tomography (CT) scan without concurrent pleural effusion. His situation was eventually stabilized by expeditious management, including selective renal arterial embolization. Despite good hemodialysis adequacy and stringent volume control, a CT scan 1 mo later found further enlargement of the perirenal hematoma with heterogeneous hypodense fluid, left side pleural effusion and a small amount of ascites. These fluid collections showed a CT density of 3 Hounsfield units, and drained fluid of the pleural effusion revealed a dubiously light-colored transudate with lymphocytic predominance (> 80%). Similar results were found 3 mo later, during which time the patient was free of pulmonary infection, cardiac dysfunction and overt hypoalbuminemia. After careful consideration and exclusion of other possible causative etiologies, we believed that the pleural effusion was due to the occlusion of renal lymphatic ducts by the compression of kidney parenchyma and, in the absence of typical dilation of the related ducts, considered our case as extrarenal lymphangiectasia in a broad sense.

CONCLUSION

As such, our case highlighted a morbific passage between the kidney and thorax under an extraordinarily rare condition. Given the paucity of pertinent knowledge, it may further broaden our understanding of this rare disorder.

Immunoglobulin G4-related Disease of the Genitourinary System: Spectrum of Imaging Findings and Clinical-Pathologic Features

Immunoglobulin G4-related disease (IgG4-RD) is a systemic fibroinflammatory disease characterized by focal or diffuse organ infiltration of IgG4-bearing plasma cells. The diagnosis of IgG4-RD is based on a combination of clinical, serologic, radiologic, and histopathologic findings. IgG4-RD has been reported to affect almost all organ systems. The kidney is the most frequently involved of the genitourinary organs. The most common renal manifestation of IgG4-RD is IgG4-RD tubulointerstitial nephritis, followed by membranous glomerulonephropathy and, less frequently, obstructive nephropathy involving the renal pelvis, ureter, or retroperitoneum. Renal parenchymal lesions may appear as multiple nodular lesions, diffuse patchy infiltrative lesions, or a single nodular lesion. Multiple small nodular cortical lesions are the most common imaging findings of IgG4-RD involving the kidney. Renal pelvic, sinus, or perinephric lesions can also occur. IgG4-RD involvement of other genitourinary organs including the ureter, bladder, urethra, and male and female reproductive organs is rare compared with kidney involvement but may show variable imaging findings such as a localized mass within or surrounding the involved organ or diffuse enlargement of the involved organ. Imaging findings of IgG4-RD involving the genitourinary system are nonspecific but should be differentiated from inflammatory and neoplastic lesions that mimic IgG4-RD. The online slide presentation from the RSNA Annual Meeting is available for this article. ^©RSNA, 2020.

Primary and secondary diseases of the perinephric space: an approach to imaging diagnosis with emphasis on MRI

The perinephric space is the middle compartment of the retroperitoneum, containing the kidneys and adrenal glands. Differential considerations for diseases involving primarily the perinephric space differ from those arising from the kidney itself, show variant imaging features, and require identification and characterisation by interpreting radiologists-an imaging diagnosis can be suggested in many cases. Lymphangiomas are congenital cystic lesions that may contain lipid-laden chyle, which may be detectable on magnetic resonance imaging (MRI). Retroperitoneal fibrosis, Erdheim-Chester disease, and lymphoma may present as a perinephric soft tissue rind. Osseous findings favour Erdheim-Chester, ureteric obstruction favours retroperitoneal fibrosis, and associated lymphadenopathy with mass-effect, but without invasion of adjacent structures favours lymphoma. Extramedullary haematopoiesis and brown fat stimulation are both characterised by signal drop on opposed-phase T1-weighted (W) images, the former resulting from severe anaemia and the latter in the context of elevated serum catecholamines, especially in the setting of phaeochromocytoma. Liposarcoma is the most common primary sarcoma of the retroperitoneum. Metastases are uncommon; however, they can be seen in melanoma, among other primary malignancies. Increased T1W signal hyperintensity is typical of melanoma metastases and haematomas. Abscesses show non-enhancing fluid centrally with marked diffusion restriction. This article presents a review of the perinephric space, pathological conditions of the perinephric space, and an approach towards imaging and diagnosis using cross-sectional imaging, with emphasis on MRI. MRI provides better tissue characterisation, assessment of enhancement kinetics, and detection of intralesional fat in comparison to CT. Clinical and laboratory correlation or tissue sampling may be required for definitive diagnosis in some cases.

Perinephric myxoid pseudotumor of fat: A very rare entity that can mimic a renal cyst and retroperitoneal liposarcoma on imaging

We present a case of perinephric myxoid pseudotumor of fat, a rare benign entity that often occurs in patients with non-neoplastic renal disease. In our case, an 80 year old man with end-stage renal disease was imaged over the course of 5 years during evaluation for renal transplantation. Imaging identified a left perinephric mass whose appearance over time and on different imaging modalities variably suggested a simple cyst, cystic neoplasm, and liposarcoma. Contrast enhanced examination was necessary to discern the solid nature of this mass, and ultimately, tissue sampling with histopathologic evaluation and molecular testing were required to make the diagnosis of myxoid pseudotumor of fat and exclude the imaging mimics.

Marrow outside marrow: imaging of extramedullary haematopoiesis

Extramedullary haematopoiesis (EMH) refers to the formation of non-neoplastic blood cell lines outside the bone marrow and is a common incidental finding when patients with haematological disorders are imaged. EMH presenting as mass (tumefactive EMH) has long been a radiological conundrum as it resembles neoplasms. Several imaging findings have been described in EMH, and these vary depending on the activity of the underlying haematopoiesis. The older lesions are easier to diagnose as they often demonstrate characteristic findings such as haemosiderin and fat deposition. In comparison, the newer, actively haematopoietic lesions often mimic neoplasms. Molecular imaging, particularly ^99mTc labelled sulphur colloid scintigraphy, may be helpful in such cases. Although imaging is extremely useful in detecting and characterising EMH, imaging alone is often non-diagnostic as no single mass shows all the typical findings. Hence, a judgement based on the clinical background, combination of imaging findings, and slow interval growth may be more appropriate and practical in making the correct diagnosis. In every case, an effort has to be made in providing an imaging-based diagnosis as it may prevent a potentially risky biopsy. When confident differentiation is not possible, biopsy has to be resorted to. This article describes the causes, pathophysiology, and theories underlying the genesis of EMH, followed by the general and location-specific imaging findings. The purpose is to provide a thorough understanding of the condition as well as enable the clinical radiologist in making an imaging-based diagnosis whenever possible and identify the situations where biopsy has to be performed.

MR imaging to detect myelolipomas of the liver: A case report and literature review

RATIONALE

Primary hepatic myelolipoma is a rare benign neoplasm comprising mature adipose tissue and marrow components in various proportions. Chemical shift imaging (CSI) can distinguish the lipid within the tumor clearly; however, there have been no reports on the CSI of hepatic myelolipoma.

PATIENT CONCERN

A 20-year-old woman visited our hospital after discovering a space-occupying lesion in the liver with a history of more than 1 year. She felt distension pain and discomfort under the xiphoid process, accompanied by nausea, vomiting, and occasional chest oppression.

DIAGNOSIS

The tumor showed a well-defined mass with a pseudocapsule and a heterogeneous appearance on both T1- and T2-weighted magnetic resonance (MR) images. CSI analysis showed a signal decline within the tumor. Based on the histopathology, the tumor was diagnosed as hepatic myelolipoma.

INTERVENTIONS AND OUTCOMES

The patient underwent a right hepatectomy, and the postoperative vital signs were stable. Two weeks later, the patient was discharged safely.

LESSONS

Although hepatic myelolipoma is extremely rare, this condition should be considered in differential diagnosis when CSI shows that hepatic lesions contain fatty.

Computed tomography and magnetic resonance imaging of peripelvic and periureteric pathologies

Peripelvic and periureteric areas are frequently overlooked in the imaging evaluations of the urinary system on computed tomography and magnetic resonance imaging. Several neoplastic and non-neoplastic disorders and diseases including lipomatosis, angiomyolipoma and angiolipomatous proliferation, vascular lesions, lymphangiomatosis, Rosai-Dorfman disease, Erdheim-Chester disease, extramedullary hematopoiesis, IgG4-related disease, lymphoma, mesenchymal tumors, trauma, and Antopol-Goldman lesion may involve these areas. Differentiation of these benign or malignant pathologies among themselves and from primary renal pathologies is of utmost importance to expedite the triage of patients for correct treatment approach. In this article, we aim to increase the awareness of the imaging specialists to the typical and atypical imaging features of the entities affecting these areas.

Secondary Tumors of the Urinary System: An Imaging Conundrum

Imaging features of metastases to the urinary system may closely mimic primary urinary tract tumors, and differential diagnosis by imaging alone may be problematic or even impossible in some cases. The main purpose of this article was to familiarize radiologists with imaging findings of metastasis to the urinary system on cross-sectional imaging, with an emphasis on abdominal and pelvic computed tomography and magnetic resonance imaging. In addition, we review the clinical importance and implications of metastases to the urinary tract and provide information on diagnostic work-ups.

Spectrum of Xanthogranulomatous Processes in the Abdomen and Pelvis: A Pictorial Review of Infectious, Inflammatory, and Proliferative Responses

OBJECTIVE

Xanthogranulomatous (XG) processes are rare inflammatory conditions with the characteristic pathologic feature of lipid-laden macrophages or histiocyte cells. Imaging findings are nonspecific and can simulate aggressive neoplastic processes. XG processes can be caused by infection, inflammation, histolytic process, or an inherited lysosomal disorder. XG infectious processes are mainly seen in cholecystitis and pyelonephritis, but several other organs can also be involved. Histiocytic processes can be divided into Langerhans and non-Langerhans cell histiocytosis. The non-Langerhans cell histiocytosis entities include Erdheim-Chester disease, Rosai-Dorfman disease, juvenile xanthogranuloma, and hemophagocytic lymphohistiocytosis. The inherited lysosomal disorders resulting in XG processes include Nieman-Pick, Gaucher, and other lysosomal storage disorders.

CONCLUSION

Radiologists need to be able to recognize features of xanthogranulomatous processes to help facilitate patient management.

Radiological diagnosis of perinephric pathology: pictorial essay 2015

The perinephric space, shaped as an inverted cone, sits between the anterior and posterior renal fasciae. It can play host to a variety of clinical conditions encountered daily in the reporting schedule for a radiologist. Lesions may be classified and diagnosed based on their imaging characteristics, location and distribution. A broad range of differential diagnoses can be attributed to pathology sitting within this space, often without clinical signs or symptoms. An understanding of commonly encountered conditions affecting the perinephric space, along with characteristic imaging findings, can illustrate and often narrow the likely diagnosis. The aim of this essay is to describe commonly encountered neoplastic and non-neoplastic entities involving the perinephric space and to describe their key imaging characteristics.

TEACHING POINT

• Despite often a bulky disease, perinephric lymphoma does not produce obstruction or stenosis. • In primarily fatty masses, defects within the renal capsule likely represent angiomyolipoma. • Consider paraganglioma if biopsy is planned; biopsy may lead to catecholamine crisis.

Fibrose rétropéritonéale: revue de littérature

La fibrose rétropéritonéale (FRP) est une maladie rare, caractérisée par la présence d’un tissu fibro-inflammatoire aberrant qui se forme souvent autour de la portion sous-rénale de l’aorte abdominale et des artères iliaques. Une obstruction urétérale est souvent observée. Récemment, la FPR idiopathique est rapportée parmi les manifestations de la maladie à IgG4. L’imagerie joue un rôle important dans le diagnostic de la FRP. Les glucocorticoïdes sont le traitement de référence, utilisés en monothérapie ou en association avec d’autres agents médicamenteux. En cas d’échec des mesures conservatrices, la chirurgie peut être proposée. Récemment, des techniques minimalement invasives ont été utilisées.

Role of multimodality imaging in the diagnosis of lymphoproliferative malignancies and hematologic disorders of the kidneys

Lymphoproliferative and hematologic disorders of the kidney may present with focal or diffuse renal parenchymal involvement in clinical practice. Radiologic findings of lymphoproliferative and hematologic disorders of the kidney may mimick primary neoplastic and inflammatory disorders of the kidney. All cross-sectional imaging modalities including ultrasonography, computed tomography, and magnetic resonance imaging may be used in the diagnosis of these diseases. Percutaneous biopsy may be used in problematic cases for definitive diagnosis.

Case 237: Renal Cell Carcinoma with Osseous Metaplasia

History A 47-year-old man presented with palpitations and decreased exercise tolerance. A peripheral blood smear revealed anemia, thrombocytopenia, and blast cells, and a diagnosis of acute myeloid leukemia was made. Immunohistochemistry revealed positivity for cluster of differentiation (or CD) markers, which have been reported to be associated with an increased risk of extramedullary leukemic involvement. Thus, contrast material-enhanced computed tomography (CT) of the thorax, abdomen, and pelvis was requested to enable exclusion of any extramedullary extension of leukemia. Unenhanced and contrast-enhanced nephrographic phase CT was performed. Follow-up CT 3 months later showed minimal interval change in the lesion (images not shown).

Synchronous occurrence of a hepatic myelolipoma and two hepatocellular carcinomas

Myelolipoma is a rare tumor composed of fat and bone marrow components, most of which are located in the adrenal gland. Myelolipoma in the liver is extremely rare. To date, only 10 cases have been reported in the English-language medical literature. In one of these cases, the hepatic myelolipoma was found within a hepatocellular carcinoma (HCC). In the present study, we report the first case of the synchronous occurrence of hepatic myelolipoma and HCCs in different liver sections of one patient, a 26-year-old female who was admitted to our hospital because of a 4-d history of upper abdominal pain. The unenhanced computed tomography (CT) images showed a well-defined low-density mass with adipose components in the right liver lobe, 4.2 cm × 4.1 cm in size. Two inhomogeneous low-density masses were found in the left liver lobe, 8.6 cm × 7.7 cm and 2.6 cm × 2.6 cm in size. The masses in both the right and left liver lobes were heterogeneously enhanced in the contrast-enhanced CT images. Based on the results of the imaging examination, the mass in the right liver lobe was preliminarily considered to be a hamartoma, and the two masses in the left liver were preliminarily considered to be HCCs. We performed a right hepatectomy, a left hepatic lobectomy, and a cholecystectomy. Microscopic and immunohistochemical results revealed that the tumor in the right liver lobe was a hepatic myelolipoma, and that the two tumors in the left liver lobe were HCCs.

Laparoscopic Radiofrequency Ablation Combined with Surgical Excision for Exophytic Renal Angiomyolipoma: A Novel Technique Based on Tumor Vasculature Features of Enhancing Renal Masses Toward Hilar Off-Clamping Nephron-Sparing Surgery

OBJECTIVES

Symptomatic angiomyolipoma (AML) and asymptomatic AML larger than 4 cm in size are usually treated with nephron-sparing surgery or transarterial embolization. We used radiofrequency ablation to treat the vascular pedicle of exophytic AML with low R.E.N.A.L. nephrometry score and investigated its feasibility for hilar off-clamping nephron-sparing surgery.

METHODS

Contrast-enhanced computed tomography (CT) showed enhanced, well-defined lipomatous tumors with a maximum diameter of 4-8 cm in the kidney of 15 patients. Results indicated that the exophytic tumors featured in the enlarged tumor vasculatures extended into the parenchyma of the involved kidney. The patients underwent radiofrequency ablation by using a Cool-tip™ probe placed into the root of the AML mass from different directions under laparoscopic ultrasonography guidance. After sealing the vascular pedicle of the tumor, the bloodless tumors were resected en bloc without renal hilar clamping or suturing the resection defect of the kidney.

RESULTS

All patients underwent the procedure smoothly, and no perioperative complications occurred. The contrast-enhanced CT scan showed small defects in the contrast-enhanced renal parenchyma at third month after the procedure, and the decrease in function of the treated kidneys was <10% during the 12-month follow-up.

CONCLUSIONS

Our initial experience suggests that sealing the tumor vessels by radiofrequency ablation based on the tumor vasculature features of a renal mass is an alternative to hilar clamping in laparoscopic nephron-sparing surgery. Laparoscopic radiofrequency ablation and tumor excision are a definitive and safe minimally invasive procedure that allows the successful removal of exophytic sporadic AML mass with low R.E.N.A.L. nephrometry score.

Erdheim-Chester disease with bilateral Achilles tendon involvement

Erdheim-Chester disease (ECD) is a rare non-Langerhans cell histiocytosis with a broad spectrum of organ manifestations, presenting with characteristic radiological and histological findings. Soft tissue manifestations (xanthogranulomas) have been reported to be most commonly found in the region of the orbits. We report bilateral Achilles tendon xanthogramlomas in a 36-year-old male with biopsy-proven and B-RAF V600E-positive ECD. Although rare, ECD should be considered in the differential diagnosis of intratendinous masses.

Spectrum of abdominal imaging findings in histiocytic disorders

OBJECTIVES

The present article provides an overview of the spectrum of abdominal findings of histiocytic disorders that may be observed in multimodality imaging illustrated by clinical cases from our Imaging Center.

METHODS

We will review abdominal findings of Langerhans cell histiocytosis, Rosai-Dorfman disease, Erdheim-Chester disease, and hemophagocytic syndrome illustrated by clinical cases from our imaging department with histologic correlation.

RESULTS

Abdominal involvement of histiocytic disorders is rare and may occur in the liver, biliary tract, kidney, retroperitoneum, kidney, gastrointestinal tract, and lymph nodes.

CONCLUSION

Histiocytic disorders encompass a group of rare diseases with a wide range of manifestations in which the abdominal involvement is quite infrequent. The role of the radiologist is to report the major imaging findings and the differential diagnosis; however, the imaging features are unspecific and biopsy usually is necessary to establish the definitive diagnosis.

Magnetic Resonance Imaging of Perirenal Pathology

The perirenal space can be involved by a variety of neoplastic, inflammatory, infectious, and proliferative disorders. Magnetic resonance imaging is often an ideal technique for identification and staging of lesions arising within the perirenal space, with its superior soft tissue characterization as well as its ability to visualize extension into blood vessels and adjacent organs. This pictorial essay describes the magnetic resonance imaging appearance of a variety of pathologies which can arise from or involve the perirenal space, and provides a framework for categorization and differential diagnosis of these lesions.

Perirenal PEComa: Computed Tomography Findings and Differential Diagnosis

The World Health Organization defines perivascular epithelioid cell tumors (PEComas) as mesenchymal tumors and tumor-like conditions composed of epithelioid cells with a perivascular distribution. These tumors may show benign or malignant histology and/or biological behavior. However, the pathological features of malignancy may not correlate with biologic aggressiveness, and the criteria for malignancy are not clearly defined. Abdominopelvic PEComas are very rare and have been reported in various locations, including kidney, liver, pancreas, gastrointestinal tract, genitourinary tract, peritoneum, and retroperitoneum. Cross-sectional imaging techniques, including computed tomography (CT) may play an important role in the accurate detection and characterization of these tumors. We present the third case of an extremely rare PEComa with perirenal location, discuss CT findings and differential diagnosis.

Advances of multidetector computed tomography in the characterization and staging of renal cell carcinoma

Renal cell carcinoma (RCC) accounts for approximately 90%-95% of kidney tumors. With the widespread use of cross-sectional imaging modalities, more than half of RCCs are detected incidentally, often diagnosed at an early stage. This may allow the planning of more conservative treatment strategies. Computed tomography (CT) is considered the examination of choice for the detection and staging of RCC. Multidetector CT (MDCT) with the improvement of spatial resolution and the ability to obtain multiphase imaging, multiplanar and three-dimensional reconstructions in any desired plane brought about further improvement in the evaluation of RCC. Differentiation of RCC from benign renal tumors based on MDCT features is improved. Tumor enhancement characteristics on MDCT have been found closely to correlate with the histologic subtype of RCC, the nuclear grade and the cytogenetic characteristics of clear cell RCC. Important information, including tumor size, localization, and organ involvement, presence and extent of venous thrombus, possible invasion of adjacent organs or lymph nodes, and presence of distant metastases are provided by MDCT examination. The preoperative evaluation of patients with RCC was improved by depicting the presence or absence of renal pseudocapsule and by assessing the possible neoplastic infiltration of the perirenal fat tissue and/or renal sinus fat compartment.

Case 214: Adrenal pheochromocytoma with perirenal brown fat stimulation

History A 61-year-old woman with well-controlled diabetes presented with a 10-year history of hypertension, stifling sensation, and flushing. Her body mass index was 19.1 kg/m(2) (normal range, 18.5-25.0 kg/m(2)). She was being followed up for mild hypercalcemia (calcium level, 10.8 mg/dL [2.7 mmol/L]) (normal range, 8.5-10.5 mg/dL [2.12-2.62 mmol/L]) by the endocrinologist (S.J.M.), who decided to perform a technetium 99m sestamibi ((99m)Tc MIBI) parathyroid scan. The test showed an abnormal tracer deposit in the region of the clavicle and sternum; thus, unenhanced thoracic computed tomography (CT) was performed. No mass was seen in the region of abnormality. In light of these findings, the patient underwent contrast material-enhanced (120 mL of iopromide, Ultravist 300; Schering, Berlin, Germany) thoracic abdominopelvic CT. There was no history of underlying malignancy, and the complete blood counts were normal. The axial and appendicular skeleton showed no sign of lesions.

Mimickers of neoplasm on abdominal and pelvic CT

PURPOSE

The radiologist can encounter benign significant imaging findings on computed tomography that can be incorrectly interpreted as neoplasm. The authors review several benign findings and demonstrate several methods to differentiate these findings from more sinister pathology.

CONCLUSION

It is imperative for the radiologist to be cognizant of and how to correctly identify mimickers of pathology so that unnecessary interventions and surgeries are avoided.

Thoracic, abdominal and musculoskeletal involvement in Erdheim-Chester disease: CT, MR and PET imaging findings

BACKGROUND

Erdheim-Chester disease (ECD) is a rare, non-Langerhans cell histiocytosis with characteristic radiological and histological features. This entity is defined by a mononuclear infiltrate consisting of lipid-laden, foamy histiocytes that stain positively for CD68 and negatively for CD1a. Osseous involvement is constant and characteristic. Extra-osseous lesions may affect the retroperitoneum, lungs, skin, heart, brain and orbits.

METHODS

Both radiography and technetium-99m bone scintigraphy may reveal osteosclerosis of the long bones, which is a typical finding in ECD. For visceral involvement, computed tomography (CT) is most useful, while magnetic resonance (MR) imaging is more sensitive for cardiovascular lesions; 2-[fluorine-18] fluoro-2-deoxy-d-glucose (FDG) positron emission tomography (PET)/CT scanning is useful in assessing the extension of ECD lesions.

RESULTS

The prognosis is extremely variable and is often worse when there is cardiovascular system involvement. Diagnosis is based on the combination of radiographic, CT, MR imaging and nuclear medicine features and a nearly pathognomonic immunohistochemical profile.

CONCLUSION

The aims of this work are to perform a systematic review of Erdheim-Chester disease as seen on imaging of the chest, abdomen and musculoskeletal system and to discuss the diagnostic workup and differential diagnoses according to the imaging presentation. Teaching points • Bone involvement is usually present in patients, and the imaging findings are pathognomonic of ECD. • The circumferential periaortic infiltration may extend to its branches, sometimes becoming symptomatic. • Cardiac involvement-the pericardium, right atrium and auriculoventricular sulcus-worsens its prognosis. • Perirenal infiltration extending to the proximal ureter is highly suggestive of this disease.

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.

Perirenal fat invasion on renal cell carcinoma: evaluation with multidetector computed tomography-multivariate analysis

OBJECTIVE

The objective of this study was to assess the accuracy of multidetector computed tomography (CT) in diagnosing perinephric (PN) and/or renal sinus (RS) fat invasion in patients with renal cell carcinoma (RCC), with reference to the CT findings predictive for the diagnosis of invasion.

METHODS

This was a retrospective study of 48 RCCs. Examinations were performed on a 16-row CT scanner, including unenhanced and 3-phase contrast-enhanced CT scanning. Unenhanced transverse images and multiplanar reformations of each contrast-enhanced CT phase were evaluated. The predictive value of CT findings in diagnosing PN and/or RS fat invasion was determined using multivariate logistic regression analysis.

RESULTS

The CT findings that were most predictive for the diagnosis of PN fat invasion were the presence of contrast-enhancing nodules in the PN fat and tumoral margins. Invasion of the pelvicaliceal system was the most significant predictor in the diagnosis of RS fat invasion.

CONCLUSIONS

Multidetector CT provides satisfactory results in detecting PN and/or RS fat invasion in RCC.

Intracranial extramedullary hematopoiesis: a rare cause of headaches

BACKGROUND

Ectopic bone marrow production, known as extramedullary hematopoiesis, may result in symptoms due to compression on normal structures. We present the multimodality imaging findings and subsequent management of a rare case of symptomatic extramedullary hematopoiesis within the calvarium.

METHODS

Case report.

RESULTS

A 54-year-old male with a history of myelofibrosis and no previous diagnosis of a headache disorder presented to the emergency department with worsening severe bilateral headaches. A nonenhanced CT of the brain was performed and diffuse extra-axial nodular hyperdensities were visualized. MRI of the brain demonstrated diffuse extra-axial avidly enhancing nodular masses, dural thickening and marked susceptibility. No paravertebral masses, typical for extramedullary hematopoiesis, were present in the chest or abdomen. Although the clinical team considered a biopsy to confirm the diagnosis, we suggested a noninvasive confirmatory test. The subsequent Tc99m sulfur colloid scan corroborated the diagnosis. The patient was then referred to radiation oncology for treatment.

CONCLUSION

In summary, extramedullary hematopoiesis is a hematologic compensatory disorder that rarely occurs within the CNS and may cause neurological compromise due to compression on underlying structures. The diagnosis can be made with noninvasive imaging and treated with low dose radiation therapy.

Acute conditions affecting the perinephric space: imaging anatomy, pathways of disease spread, and differential diagnosis

The perinephric space is an important, central compartment of the retroperitoneum which may host various acute conditions. Imaging evaluation of the perinephric space requires an understanding of its anatomy and the pathways of disease spread to and from other retroperitoneal compartments. Numerous acute conditions can affect the perinephric space and may occur in isolation, extend from nearby retroperitoneal structures, or be part of a systemic condition. Familiarity with the key imaging findings of acute conditions affecting the perinephric space is imperative to facilitate diagnosis and guide treatment. The purpose of this article is to review and illustrate the relevant anatomy, pathways of disease spread, and acute pathology encountered during cross-sectional imaging evaluation of the perinephric space.