The lateral margin of the psoas muscle, contrasted by retroperitoneal fat, is usually visualized o plainabdominal radiography. Failure to visualize all or segment of lateral margin of the psoas muscle, so called psoassing, has been emphasized as reliable finding of retroperitoneal pathology. But the significance of psoas sign hasbeen controversial. The authors reevaluated ‘psoas sign’ by comparing 160 abdominal radiography with CT. Theresults were as follows: 1. In 160 supine radiographys, good visualization was present in 106 cases(66.3%), faintvisualizatin in 24(15.0%), segmental nonvisualization in 18(11.3%), and completer nonvisualization in 12(7.5%). In113 erect radiographs, good visualization was present in only 36 cases(31.9%). 2. Asymmetric visualization waspresent in 84 out of 160 cases. In patient with scoliosis, lateral margin of convex side was seen more clearlythan concave side, and this finding was statistically significant (p<0.005). 3. Ascites did not directly influenceto psoa visualization contrary to common belief. 4. In 54 cases of faint or nonvisualization, normal was16(29.6%), intraperitoneal pathology was 16(29.6%), and retroperitoneal pathology was 22(40.7%). 1) In normalpatient, psoas contact with kidney or intestine and deformed psoas muscle were responsible for poor visualization. 2) The major cause of poor visualization in intraperitoneal pathology were psoas contact with displaced kidney byhepatomegaly, ascites with scanty retroperitoneal fat and derformed psaos muscle. 3) The major cause of poorvisualization in retroperitoneal pathology were psoas invasion by tumor or inflammation, psoas conntact withenlarged kidney or perirenal lesion. 5. In summary, the mechanism of faint or nonvisualization of psoas marginwere: 1) psoas contact with normal or pathologic organs 2) psoas invasion by tumor or inflammation 3) deformedpsoas muscle 4) scanty retroperitoneal fat
Ascites ; Humans ; Inflammation ; Intestines ; Intra-Abdominal Fat ; Kidney ; Pathology ; Psoas Muscles ; Radiography ; Radiography, Abdominal ; Scoliosis

The prevalence of small renal masses (SRM) has risen, paralleling the increased usage of cross-sectional imaging. A large proportion of these SRMs are not malignant, and do not require invasive treatment such as nephrectomy. Therefore, differentation between early renal cell carcinoma (RCC) and benign SRM is critical to achieve proper management. This article reviews the radiological features of benign SRMs, with focus on two of the most common benign entities, angiomyolipoma and oncocytoma, in terms of their common imaging findings and differential features from RCC. Furthermore, the role of percutaneous biopsy is discussed as imaging is yet imperfect, therefore necessitating biopsy in certain circumstances to confirm the benignity of SRMs.
Abdominal Fat/pathology ; Adenoma, Oxyphilic/diagnosis/radiography/ultrasonography ; Angiomyolipoma/diagnosis/radiography/ultrasonography ; Carcinoma, Renal Cell/*diagnosis/radiography/ultrasonography ; Diagnosis, Differential ; Humans ; Kidney Neoplasms/*diagnosis/*radiography/ultrasonography ; Leiomyoma/diagnosis/radiography/ultrasonography

There are a variety of fat-containing lesions that can arise in the intraperitoneal cavity and retroperitoneal space. Some of these fat-containing lesions, such as liposarcoma and retroperitoneal teratoma, have to be resected, although resection can be deferred for others, such as adrenal adenoma, myelolipoma, angiomyolipoma, ovarian teratoma, and lipoma, until the lesions become large or symptomatic. The third group tumors (i.e., mesenteric panniculitis and pseudolipoma of Glisson's capsule) require medical treatment or no treatment at all. Identifying factors such as whether the fat is macroscopic or microscopic within the lesion, the origin of the lesions, and the presence of combined calcification is important for narrowing the differential diagnosis. The development and wide-spread use of modern imaging modalities make identification of these factors easier so narrowing the differential diagnosis is possible. At the same time, lesions that do not require immediate treatment are being incidentally found at an increasing rate with these same imaging techniques. Thus, the questions about the treatment methods have become increasingly important. Classifying lesions in terms of the necessity of performing surgical treatment can provide important information to clinicians, and this is the one of a radiologist's key responsibilities.
Abdominal Fat/pathology/radiography ; Adult ; Aged ; Diagnosis, Differential ; Female ; Humans ; Magnetic Resonance Imaging/methods ; Male ; Middle Aged ; Neoplasms, Adipose Tissue/*pathology/*radiography ; Peritoneal Cavity/pathology/radiography ; Peritoneal Diseases/pathology/radiography ; Peritoneal Neoplasms/*pathology/*radiography ; Retroperitoneal Neoplasms/*pathology/*radiography ; Retroperitoneal Space/pathology/radiography ; Tomography, Spiral Computed/methods ; Young Adult