Does the presence of focal normal marrow fat signal within a tumor on MRI exclude malignancy? An analysis of 184 histologically proven tumors of the pelvic and appendicular skeleton.

OBJECTIVE: The aim of this study was to determine if the presence of focal normal bone marrow fat signal within a tumor on magnetic resonance imaging excludes malignancy. MATERIALS AND METHODS: One hundred eighty-four histologically proven tumors with available magnetic resonance imaging (MRI) of the appendicular skeleton and pelvis from 184 patients were collected and reviewed at two separate institutions. There were 111 malignant and 73 benign tumors. Two radiologists at each institution, blinded to the diagnosis, reviewed the MRIs independently and reported the presence or absence of normal marrow fat signal within the tumor based upon T1-weighted imaging without fat suppression and T2-weighted imaging with fat suppression and/or short inversion-time inversion recovery (STIR). Discrepancies were then reviewed in consensus to determine the presence or absence of focal normal marrow signal. For each institution, a Fisher's exact test was used to compare the frequency of focal normal marrow fat signal in benign and malignant tumors. This comparison was performed for each reader, as well as for the consensus reading at each site. Positive and negative predictive values were also calculated for each reader, as well as the consensus reading at each site. Fisher's exact test was also used to compare the frequency of intratumoral fat in benign and malignant lesions for the pooled sample. Bayes theorem was used to calculate the positive and negative predictive values for the pooled consensus data. Ninety-five percent confidence intervals were constructed for the pooled estimates using a bootstrapping algorithm. RESULTS: There was good interobserver reliability of 95.3% and 96.7% at sites 1 and 2, respectively. There were three discrepancies (one malignant and two benign) at site 1 and four discrepancies (two malignant and two benign) at site 2. Reader consensus at site 1 identified normal marrow fat signal within 1 of 50 (2.0%) malignant and three of 14 (21.4%) benign tumors. Findings were statistically significant with a p value of 0.030. The positive predictive value (PPV) and negative predictive value (NPV) at site 1 was 81.7% and 75.0%, respectively. Reader consensus at site 2 identified normal marrow fat signal within three of 61 (4.9%) malignant and 14 of 59 (23.7%) benign tumors. Findings were statistically significant with a calculated p value of 0.004. The PPV and NPV at site 1 was 56.3% and 82.4%, respectively. For the pooled consensus, the frequency of intratumoral fat in benign lesions (17/73, 23.3%) is significantly greater than the frequency in malignant lesions (4/111, 3.6%), p < 0.001. CONCLUSION: The presence of focal normal marrow signal within a tumor is highly suggestive of a benign tumor.

Intraosseous myelolipoma.

Two patients with lesions in the acetabulum and femur, evident on imaging, were found to have normal marrow elements without a histopathological lesion on curettage of the acetabulum and resection of the femur, respectively. Radiographs on the first patient showed a sclerotic benign appearing acetabular lesion reminiscent of a fibro-osseous lesion while MRI showed the entire lesion to contain fat. The histological features were neither of a fibro-osseous lesion nor a lipoma, but only normal to mildly hypercellular marrow elements. The second patient had a long and expansive femoral osteolytic lesion which on biopsy showed cellular marrow. A subsequent stress fracture led to resection and prosthetic replacement. Microscopic findings revealed only cellular hematopoietic marrow with mature red and white cell lines, megakaryocytes, and a few mast cells devoid of trabecular bones. The microscopic features in the first patient raised the possibility of hematopoietic hyperplasia. Neither the radiographic nor MRI features were consistent with that diagnosis. The spectrum of imaging findings and microscopic appearances in both patients best fit the diagnosis of intraosseous myelolipoma.

Unilateral hypertrophy of tensor fascia lata: a soft tissue tumor simulator.

OBJECTIVE: To describe the imaging findings in eight cases of unilateral tensor fascia lata (TFL) hypertrophy presenting as soft tissue masses. DESIGN: Imaging studies and medical charts of eight patients were reviewed retrospectively. The imaging studies included five radiographs, five computed tomography (CT) and six magnetic resonance imaging (MRI) examinations. RESULTS: The majority of patients (seven of eight) presented with a palpable proximal anterior thigh mass. One patient was asymptomatic and incidentally diagnosed. There were six females and two males. Ages ranged from 27 to 86 years old (mean 61). MRI and CT showed unilateral enlargement of the TFL muscle in all cases. CONCLUSION: TFL muscle hypertrophy is an uncommon clinical entity, which can simulate a soft tissue tumor. The characteristic appearance on CT or MRI allows a confident diagnosis of muscle hypertrophy to be made, avoiding unnecessary biopsy or surgical intervention.

Work-up of urinary tract infection in infants and children.

Urinary tract infection (UTI) in infants and children demands rapid differentiation between upper UTI (pyelonephritis) and lower UTI (cystitis) for prompt treatment to be initiated so that renal damage is minimized. This pictorial review presents a wide gamut of structural and functional abnormalities of the urinary tract that may predispose infants and children to UTI, including vesicoureteral reflux, upper urinary tract obstruction (ureteropelvic junction obstruction), lower urinary tract obstruction (primary megaureter, ureterovesical junction obstruction, posterior urethral valve, ectopic ureterocele with or without associated duplex collecting system), neurogenic problems (dysfunctional voiding), calculi, and parenchymal scars. Sonography (ultrasound [US]) is the imaging modality of choice for assessment of renal size, growth (serial sonograms), texture, and blood flow. Other modalities used to work-up UTI in the pediatric patient include fluoroscopic voiding cystourethrogram, nuclear voiding cystourethrogram, and nuclear renal scintigraphy (NRS). Excretory urography is no longer recommended in the routine evaluation of childhood UTI because information regarding anatomy and function (qualitative and quantitative) can be better assessed with US and NRS, respectively. Computed tomography and magnetic resonance imaging are primarily reserved for complex cases in which a definitive diagnosis cannot be made with routine imaging. Algorithms for work-up of UTI in various pediatric age groups are presented.

US approach to jaundice in infants and children.

High-resolution real-time ultrasonography (US) serves as an important tool for differentiation of obstructive and nonobstructive causes of jaundice in infants and children, independent of liver function. Unconjugated hyperbilirubinemia occurs in approximately 60% of normal term infants and in 80% of preterm infants. Persistence of neonatal jaundice beyond 2 weeks of age demands US evaluation to differentiate between the three most common causes: hepatitis, biliary atresia, and choledochal cyst. In all three conditions, the hepatic echotexture is diffusely coarse and hyperechoic, but this appearance may be seen in a variety of hepatic inflammatory, obstructive, and metabolic processes. Thus, hepatic scintigraphy and at times percutaneous liver biopsy are necessary to narrow the differential diagnosis and to identify patients who require more invasive techniques (eg, intraoperative cholangiography). US is useful for demonstrating inspissated bile and biliary duct stones. In infants, stones are usually secondary to obstructive congenital anomalies of the biliary tract, total parenteral nutrition, furosemide treatment, phototherapy, dehydration, infection, hemolytic anemia, and short-gut syndrome, whereas in older children, stones are usually associated with sickle cell disease, bowel resection, hemolytic anemia, and choledochal cyst. Jaundice in infants and children may also be due to cirrhosis, benign strictures, and neoplastic processes.