Impact of the Armed Forces Institute of Pathology Radiologic Pathology Course on radiology resident performance on the ACR In-Training and ABR written Examinations. American College of Radiology. American Board of Radiology

RATIONALE AND OBJECTIVES

The purpose of this study was to assess resident scores on the American College of Radiology (ACR) In-Training Examination and on the written American Board of Radiology (ABR) Examination relative to attendance at and timing of the Armed Forces Institute of Pathology (AFIP) Radiologic Pathology Course.

MATERIALS AND METHODS

A survey of 200 radiology residency program directors requested the type of residency program, whether the program sent residents to the AFIP course, dates of AFIP attendance for individual residents, percentile scores of residents on the ACR examination from 1995 through 1998, and ABR examination scores for 1997. Scores were analyzed before and after AFIP attendance and also temporally for examinations during or after AFIP attendance. Improvement in percentile scores for residents undergoing the ACR examination while attending the AFIP were compared with scores of matched residents from their programs who had not attended.

RESULTS

Thirty-six (18%) program directors responded, providing data on 619 residents who underwent the ACR examination, ABR examination, or both. No significant improvement was found between pre- and post-AFIP ACR Examination scores for residents at university or military programs. There were statistically significantly improved scores for residents at community programs (mean percentile improvement, 8.1 points; P = .0064). Residents who underwent the ACR examination during the AFIP course improved their scores by 10.7 percentile points compared with matched residents who had not attended the AFIP course (P = .041).

CONCLUSION

Residents undergoing the ACR examination while attending the AFIP improve their percentile scores more than residents who have not attended the AFIP.

Dopamine D4/D2 receptor selectivity is determined by A divergent aromatic microdomain contained within the second, third, and seventh membrane-spanning segments

Conserved features of the sequences of dopamine receptors and of homologous G-protein-coupled receptors point to regions, and amino acid residues within these regions, that contribute to their ligand binding sites. Differences in binding specificities among the catecholamine receptors, however, must stem from their nonconserved residues. Using the substituted-cysteine accessibility method, we have identified the residues that form the surface of the water-accessible binding-site crevice in the dopamine D2 receptor. Of approximately 80 membrane-spanning residues that differ between the D2 and D4 receptors, only 20 were found to be accessible, and 6 of these 20 are conservative aliphatic substitutions. In a D2 receptor background, we mutated the 14 accessible, nonconserved residues, individually or in combinations, to the aligned residues in the D4 receptor. We also made the reciprocal mutations in a D4 receptor background. The combined substitution of four to six of these residues was sufficient to switch the affinity of the receptors for several chemically distinct D4-selective antagonists by three orders of magnitude in both directions (D2- to D4-like and D4- to D2-like). The mutated residues are in the second, third, and seventh membrane-spanning segments (M2, M3, M7) and form a cluster in the binding-site crevice. Mutation of a single residue in this cluster in M2 was sufficient to increase the affinity for clozapine to D4-like levels. We can rationalize the data in terms of a set of chemical moieties in the ligands interacting with a divergent aromatic microdomain in M2-M3-M7 of the D2 and D4 receptors.

Renal medullary cystic disease: assessment by MRI

Medullary cystic disease is an important cause of renal failure in adolescent patients. Imaging plays a primary role in the diagnosis of this entity as cysts are characteristically seen in the renal medulla and corticomedullary junction with normal to small sized kidneys. Imaging studies that do not use intravenous contrast or ionizing radiation are particularly useful given the young age of these patients and presence of renal failure. In this case, we demonstrate the imaging findings of medullary cystic disease by MRI.

Expression and characterization of a dopamine D4R variant associated with delusional disorder

Multiple genetic polymorphisms of the human dopamine D4 receptor (hD4R) have been identified including a 12 bp repeat in exon 1 associated with a psychotic condition called delusional disorder. Competition binding assays revealed minor pharmacological differences between the recombinant A1 (normal) and A2 (delusional) proteins with respect to quinpirole and the antipsychotic clozapine, however no functional differences were detected for receptor activation by dopamine, epinephrine, or norepinephrine. Our results suggest that this polymorphism may only confer susceptibility to delusional disorder in combination with other genetic or environmental factors.

Development and characterization of antibodies against the N terminus of the human dopamine D4 receptor

The human dopamine D4 receptor (hD4R), which has been implicated in human diseases such as schizophrenia and in a personality trait called "novelty seeking," has not yet been characterized at the protein level. Following epitope scanning of the hD4R, we have produced a highly specific monoclonal antibody named DFR1 raised against an amino-terminal peptide in a predicted extracellular region of the receptor. DFR1 decorated recombinant hD4Rs on the surface of intact Chinese hamster ovary (CHO) cells by flow cytometry and fluorescence microscopy and also recognized recombinant hD4.2, hD4.4, and hD4.7 receptor isoforms by western blot analysis. When expressed stably in CHO cells, all three hD4R isoforms contained N-linked glycosylation and showed apparent molecular masses of 48, 55, and 67 kDa for hD4.2, hD4.4, and hD4.7, respectively. DFR1 immunoreactivity representing hD4R protein or dopamine D4 receptor-like antigens was observed in crude membrane extracts of postmortem human brain tissue by immunoblotting. The DFR1 antibody provides a new immunological tool with the potential to further our understanding of the human dopamine D4 receptor protein.

Renal cystic diseases

Renal cystic disease comprises a mixed group of heritable, developmental, and acquired disorders. Because of their diverse etiology, histology, and clinical presentation, no single scheme of classification has gained acceptance. Conditions include autosomal dominant polycystic kidney disease, acquired renal cystic disease, medullary sponge kidney, autosomal recessive polycystic kidney disease, multicystic dysplastic kidney, medullary cystic disease, tuberous sclerosis, cysts of the renal sinus, and von Hippel-Lindau's disease. An awareness of the pathology of each cystic disease is helpful in the understanding of the corresponding radiological images. Imaging techniques used in evaluating renal cystic disease include intravenous urography, sonography, CT, MRI, nuclear medicine, and renal angiography. Many types of cystic disease show similar imaging features. Meticulous attention to subtle radiological findings is therefore essential for reaching a correct diagnosis. Imaging features requiring analysis include whether the cysts are unilateral or bilateral, renal size and functional status, cyst distribution in the kidneys, and the presence of hemorrhagic and calcified renal cysts, solid renal masses, renal sinus cysts, and cysts in adjacent organs. Radiological findings should be carefully correlated with clinical features such as patient age, family history, symptoms, physical findings, and renal functional status before a diagnosis is attempted.

Diversity of dopamine receptors: new molecular and pharmacological developments

Five distinct dopamine (DA) receptors, named D1-D5, are expressed in the central nervous system where they control motor function, emotional states, and endocrine physiology. With the production of receptor-specific knockout mice and the development of receptor subtype specific ligands, our understanding of dopaminergic systems in the brain is expanding rapidly. In some of the more recent developments, the D4R has been shown to be activated by all three catecholamine neurotransmitters: DA, epinephrine, and norepinephrine. This functional activation by multiple neurotransmitters provides a novel mechanism for integration of catecholamine signaling. In addition, the D4R was reported last year to show genetic linkage to a personality trait called novelty seeking, and now has been implicated in the manifestation of attention deficit hyperactivity disorder, which affects 3-6% of school age children. New evidence has emerged indicating that yet another DA receptor subtype may exist which has D1-like pharmacology but couples to phosphoinositol turnover, which may be of particular importance in the light of recent studies which show decreased D1-like receptor density in brain from schizophrenic patients. This review will cover these and other new developments in the area of DA receptors which have important implications for the understanding of human behavior and disease.

Current concepts and controversies in imaging of renal cystic diseases

Renal cystic disease compromises a diverse group of inherited and acquired entities. This article reviews the clinical, pathologic, and radiologic findings of eight renal cystic diseases. For each entity, the current concepts of pathogenesis and pathophysiology are discussed. When appropriate, controversies concerning terminology, management, and malignant potentials are addressed. Renal cystic diseases that are discussed include autosomal dominant and autosomal recessive polycystic kidney disease, medullary sponge kidney, medullary cystic disease, multicystic, dysplastic kidney, von Hippel-Lindau disease, acquired cystic kidney disease, and tuberous sclerosis.

Epinephrine and norepinephrine act as potent agonists at the recombinant human dopamine D4 receptor

The catecholamines dopamine (DA), epinephrine (EP), and norepinephrine (NE) play important roles in learning and memory, emotional states, and control of voluntary movement, as well as cardiovascular and kidney function. They activate distinct but overlapping neuronal pathways through five distinct DA receptors (D1R-D5R) and at least 10 different adrenergic receptors (alpha 1a/b/c, alpha 2a/b/c-1/c-2, and beta 1/beta 2/beta 3). The D4R, which is localized to mesolimbic areas of the brain implicated in affective and emotional behavior, has a deduced amino acid sequence with homology to both adrenergic and dopaminergic receptor subtypes. We report here that DA, EP, and NE all show binding in the nanomolar range to three isoforms of the recombinant human D4R (hD4R): D4.2, D4.4, and D4.7. Submicromolar concentrations of DA, EP, and NE were sufficient to activate hD4R isoforms in two different functional assays: agonist-induced guanosine 5'-O-(3-[35S]thiotriphosphate) binding and modulation of adenylyl cyclase activity. DA was approximately fivefold more potent than EP and NE at the D4R, whereas activation of the human D2R required at least 100-fold higher catecholamine concentrations. Functional activation of the D4R by multiple neurotransmitters may provide a novel mechanism for integration of catecholamine signaling in the brain and periphery.

Radiologic assessment of renal masses: implications for patient care

The relationships between the gross pathologic features of neoplastic and nonneoplastic renal masses and their radiologic analogues, described above, establish specific guidelines for the influence of radiologic studies on clinical management. A tumor that contains fat, as determined with CT or MR imaging, can be confidently diagnosed as an angiomyolipoma without further diagnostic intervention. The size of the lesion should be used to influence clinical decisions related to the fact that angiomyolipomas larger than 4 cm in diameter are more apt to hemorrhage than those smaller than that size. High confidence can also be assigned to those renal masses that exhibit the radiologic analogues for hemangioma with use of imaging modalities that document their vascular nature. These findings should be sufficient for therapeutic decisions directed toward embolization or surgical excision when clinically warranted. If a mass can be characterized as a simple cyst by satisfying all of the required CT or sonographic criteria, no further diagnostic interventions are required. This includes the radiologic findings of thin rim of peripheral calcification and thin septa with or without calcification. An equally high level of confidence is associated with the broad range of CT, sonographic, or MR imaging findings that indicate malignant tumor. These militate for radical surgery. However, the same findings are also encountered in hemorrhagic and infected renal cyst, abscess, benign neoplasms, and inflammatory mass. Therefore, surgical excision, the nature of which will vary according to individual circumstances, is usually required to establish these diagnoses. Exceptions to the need for a tissue diagnosis might be considered in the patient in whom a renal mass is detected in the clinical setting of infection and in the patient with either a small asymptomatic renal mass or a small hyperattenuating mass that meets the other criteria of a simple cyst. Here again, individual circumstances may lead to such alternatives as aspiration of the mass for culture, interval follow-up to seek evidence of growth, or dismissal.

Molecular attributes of dopamine receptors: new potential for antipsychotic drug development

The neurotransmitter dopamine (DA) plays a central role in the control of motor function, emotional states, and endocrine physiology. The discovery that schizophrenic symptoms can be alleviated by neuroleptic drugs and the finding that these drugs interact at dopamine receptors has indicated involvement of the dopamine system in schizophrenia. The dopamine system has recently been shown to rely on the activation of five distinct subtypes of DA receptors (D1-D5) identified by molecular cloning, and pharmacological studies have specifically implicated the D2-like receptors (D2R, D3R and D4R) in antipsychotic action. In addition, the localization of D3R and D4R expression in the mesolimbic/mesocortical DA pathways is consistent with their proposed involvement in affective behaviour, and suggests that drugs developed specifically for these receptor subtypes might have potent antipsychotic activity with a lower propensity for extrapyramidal, endocrine, and cognitive side-effects.

Lack of expression of dopamine D2 receptors in malignant melanoma: evidence for interaction of iodobenzofurans with melanin

OBJECTIVES

(1) To compare scintigraphy using the new dopamine D2 receptor binding radioligand iodobenzofuran (IBF) versus whole-body positron emission tomography (PET) in demonstrating metastasizing melanoma, and (2) to determine, for the first time using a panel of histochemical techniques, whether the ability of D2 receptor binding radioligands to detect melanoma metastases is due to tumor-expressed D2 receptors.

METHODS

Seven patients with metastatic melanoma were examined using 123I-IBF scintigraphy. Findings were compared to the results of PET and metastasis histochemistry: D2 receptor mRNA assay (metastases: n = 5; melanoma cell lines: n = 4) using the reverse transcriptase polymerase chain reaction (RT-PCR) versus D2 receptor-transfected Chinese hamster ovary cell controls: in vitro 125I-IBF binding (n = 19), and immunohistochemical staining for dopamine D2 receptor protein (n = 19).

RESULTS

IBF scintigraphy detected 2/10 melanoma metastases detected by PET (sensitivity 20%). No dopamine D2 receptor mRNA was found in melanoma cells using RT-PCR. The binding of 125I-IBF correlated with the amount of melanin present in the metastases; two amelanotic melanomas both failed to bind 125I-IBF. Immunohistochemical staining was negative in all metastases.

CONCLUSION

Melanoma cells do not appear to express dopamine D2 receptors. Although IBF had high dopamine D2 receptor affinity, its ability to detect melanoma metastases is more likely explained by low affinity binding to melanin than by the presence of dopamine receptors.

Renal medullary carcinoma associated with sickle cell trait: radiologic findings

PURPOSE

To correlate the radiologic and pathologic findings in patients with renal medullary carcinoma and sickle cell trait.

MATERIALS AND METHODS

Radiologic studies of five pathologically proved cases of renal medullary carcinoma were retrospectively correlated with gross pathologic findings. Excretory urograms, computed tomographic (CT) scans, sonograms, photographs of the gross surgical specimens, and an angiogram were available for review. Each case was analyzed for tumor location, pattern of growth, contrast enhancement and echotexture, angiographic pattern, and stage.

RESULTS

All tumors arose centrally within the kidney, grew in an infiltrative pattern, and invaded the renal sinus. Caliectasis without pelviectasis was present in three cases. Contrast enhancement and echotexture were heterogeneous in all patients. Tumor necrosis with communication into the collecting system occurred in one patient. The one available angiogram demonstrated hypovascularity.

CONCLUSION

Patients with renal medullary carcinoma share particular demographic, clinical, and radiologic features that might enable radiologists to suggest a specific diagnosis.

Nerve growth factor-induced differentiation in neuroblastoma cells expressing TrkA but lacking p75NGFR

Nerve growth factor (NGF) binds to two distinct cell surface receptors, TrkA, which is a receptor tyrosine kinase, and p75NGFR, whose role in NGF-induced signal transduction remains unclear. We have found that human neuroblastoma IMR-32 cells express TrkA, but p75NGFR expression was not detectable in these cells by northern blot analysis, immunoblotting, or chemical crosslinking experiments. Despite the lack of p75NGFR expression, subnanomolar concentrations of recombinant human NGF induced neurite outgrowth, tyrosine phosphorylation, and immediate early gene expression in these cells. These results strongly suggest that NGF-induced neuronal differentiation in IMR-32 cells is initiated through TrkA in the absence of p75NGFR. Thus, IMR-32 cells may provide a model for studying neurotrophic effects of NGF on adult striatal cholinergic neurons, which also lack p75NGFR expression.

Interactive method of informing patients of the risks of intravenous contrast media

PURPOSE

To evaluate interactive computer-based informed consent for use of contrast material versus the same information in a written format.

MATERIALS AND METHODS

Patients (n = 160) referred for radiologic examination with intravenous contrast material were block randomized (sex, age, and previous exposure to contrast material) into two groups and were provided either written or computer-based (video) informed consent.

RESULTS

The female patients in the video group scored better on the test than those in the group with the written consent form. Male patients attained equivalent scores with both types of consent. The video took an average of 1.6 minutes longer to complete, probably because the majority of patients chose to be informed of every risk of intravenous contrast material.

CONCLUSION

This project demonstrates that a video format for informed consent before use of intravenous contrast material offers a good alternative to the written consent form.

Renal oncocytoma and carcinoma: failure of differentiation with CT

The authors studied the hypothesis that oncocytoma and adenocarcinoma of the kidney can be differentiated with computed tomographic (CT) criteria and that differences would become more apparent as tumors enlarged. On contrast material-enhanced scans, homogeneous attenuation throughout the tumor and a central, sharply marginated, stellate area of low attenuation were considered predictors of oncocytoma. Any area of decreased attenuation in the tumor except for a stellate, central area was used as a predictor of adenocarcinoma. Among oncocytomas larger than 3 cm in diameter, 67% exhibited the criteria for oncocytoma and 33% met the criterion for adenocarcinoma; among smaller oncocytomas, the respective results were 82% and 18%. Among adenocarcinomas larger than 3 cm in diameter, 84% fulfilled the criterion for malignancy and 16% were incorrectly predicted to be oncocytomas; among smaller adenocarcinomas, the respective results were 58% and 42%. The authors conclude that the CT criteria used are poor predictors of the diagnosis of oncocytoma or adenocarcinoma regardless of tumor size.

Multiple trkA proteins in PC12 cells bind NGF with a slow association rate

Rat pheochromocytoma (PC12) cells express two distinct nerve growth factor receptors (NGFRs), p75NGFR and trkA (p140trk). In addition to these receptors, by using 125I-mNGF affinity labeling and BS3 chemical cross-linking of PC12 cell protein, we have identified two additional trkA protein bands with apparent molecular weights of 220,000 and 300,000. These bands contain trkA, but were not immunoprecipitated by p75NGFR-specific antisera, suggesting that they do not represent trkA/p75NGFR protein complexes. The 220-kDa trkA band apparently represents trkA with alternate post-translational modification. The appearance of the 300-kDa trkA band was dependent on cross-linker concentration and could be diminished in the presence of reducing agents, suggesting that it represents a trkA dimer. All trkA bands were phosphorylated on tyrosine residues when bound to mNGF, suggesting that they participate in NGF-induced signal transduction. NGF binding kinetics to all three trkA bands were indistinguishable, with slow dissociation rates, and a slow association rate that required approximately 1 h to reach equilibrium levels at 4 degrees C. All three trkA bands bound the related neurotrophin brain-derived neurotrophic factor and neurotrophin-3 with a profile characteristic of trkA.

Renal cystic disease in multisystem conditions

Five renal cystic diseases have significant extrarenal manifestations: autosomal dominant polycystic kidney disease (ADPCK), autosomal recessive polycystic kidney disease (ARDCK), tuberous sclerosis (TS), von Hippel-Lindau Syndrome (VHL), and medullary cystic disease (MCD). Knowledge of these extrarenal manifestations is important since they may precede, present simultaneously, or follow the onset of the renal cystic disease. This article discusses the most significant extrarenal manifestations of these five renal cystic diseases: (1) ADPCK: hepatic cysts and cardiovascular abnormalities; (2) ARDCK: portal hypertension; (3) TS: hamartoma-like tumors of other organs; (4) VHL: central nervous system hemangioblastomas and paragangliomas; and (5) MCD: congenital hepatic fibrosis. Detecting extrarenal manifestations may be helpful (1) in confirming the renal cystic disease; (2) in thoroughly evaluating the patient with known renal cystic disease, and (3) if they antedate the renal cystic disease, their presence will alert the radiologist to evaluate the kidneys.

From the archives of the AFIP. Leiomyosarcoma of the retroperitoneum and inferior vena cava: radiologic-pathologic correlation

Leiomyosarcoma is the second most common primary retroperitoneal tumor in adults. Retroperitoneal leiomyosarcoma exhibits three major growth patterns: (a) completely extravascular (extraluminal) (62% of cases), (b) completely intravascular (intraluminal) (5% of cases), and (c) extra- and intraluminal (33% of cases). The usual clinical manifestation is a large abdominal mass. Intraluminal leiomyosarcoma may be accompanied by symptoms referable to venous thrombosis. The variable gross features and potential for intravascular extension result in various radiologic appearances, the most common being a large, partially necrotic soft-tissue mass in the retroperitoneum with or without extension into the inferior vena cava. Computed tomography and magnetic resonance imaging typically show a nonfatty, necrotic retroperitoneal mass and a vascular component when it is present. Ultrasound and angiography may also be useful, especially if vascular involvement is suspected from other imaging studies. Treatment of choice is surgical excision, which is frequently impossible due to the invasiveness of the tumor. Prognosis is related to extent of invasion and the adequacy of resection. Long-term prognosis is poor, and most patients die of local recurrence or distant metastasis.

Retroaortic left renal vein in testicular cancer patient: potential staging and treatment pitfall

A 20-year-old man was diagnosed with a left mixed germ cell testicular tumor and clinical staging with computerized tomography suggested left para-aortic subhilar retroperitoneal adenopathy. The patient received 4 cycles of cisplatin, vinblastine and bleomycin chemotherapy but the mass in the left renal hilus area remained unchanged. Subsequent retroperitoneal lymphadenectomy revealed the mass to be a retroaoritc left renal vein type 2. Further confusion occurred during followup in differentiating this anomaly from recurrent neoplasm necessitating evaluation by magnetic resonance imaging. Retroaortic left renal vein represents a potential imaging pitfall in testicular cancer that may facilitate suboptimal staging, treatment and followup.

Cystic renal masses: usefulness of the Bosniak classification

To determine the usefulness of the Bosniak classification of cystic renal masses, the computed tomographic (CT) and ultrasound findings of 16 pathologically proven cystic renal masses were retrospectively reviewed. All imaging studies were reviewed and categorized utilizing the Bosniak classification without knowledge of the final pathologic diagnosis. There were no category I lesions (classical simple cyst), four category II (minimally complicated), seven category III lesions (more complicated), and five category IV lesions (probable malignant). All category II lesions were benign, all category IV lesions were malignant. Of the seven category III lesions, three were benign and four were malignant. We conclude that the Bosniak classification is extremely useful in the management of cystic renal masses.

Extracellular synaptic factors induce clustering of acetylcholine receptors stably expressed in fibroblasts

The clustering of nicotinic acetylcholine receptors (AChRs) is one of the first events observed during formation of the neuromuscular junction. To determine the mechanism involved in AChR clustering, we established a nonmuscle cell line (mouse fibroblast L cells) that stably expresses just one muscle-specific gene product, the AChR. We have shown that when Torpedo californica AChRs are expressed in fibroblasts, their immunological, biochemical, and electrophysiological properties all indicate that fully functional cell surface AChRs are produced. In the present study, the cell surface distribution and stability of Torpedo AChRs expressed in fibroblasts (AChR-fibroblasts) were analyzed and shown to be similar to nonclustered AChRs expressed in muscle cells. AChR-fibroblasts incubated with antibodies directed against the AChR induced the formation of small AChR microclusters (less than 0.5 micron 2) and caused an increase in the internalization rate and degradation of surface AChRs (antigenic modulation) in a manner similar to that observed in muscle cells. Two disparate sources of AChR clustering factors, extracellular matrix isolated from Torpedo electric organ and conditioned media from a rodent neuroblastoma-glioma hybrid cell line, each induced large (1-3 microns 2), stable AChR clusters with no change in the level of surface AChR expression. By exploiting the temperature-sensitive nature of Torpedo AChR assembly, we were able to demonstrate that factor-induced clusters were produced by mobilization of preexisting surface AChRs, not by directed insertion of newly synthesized AChRs. AChR clusters were never observed in the absence of extracellular synaptic factors. Our results suggest that these factors can interact directly with the AChR.

Current status of imaging indeterminate renal masses

In 1986 Bosniak proposed a classification of cysts and cystic renal masses in an attempt to define precisely the radiologic findings for lesions not requiring further evaluation and for those that should be explored surgically in an attempt to salvage normal renal parenchyma. This classification has been extremely useful in expanding the number of patients treated conservatively. The following entities can be considered benign and require no further evaluation: the classic simple cyst (Bosniak category 1), a cyst with benign calcification (see Fig. 1A and B), a hyperdense cyst (see Fig. 2), and a cyst with thin (less than or equal to 1mm) septations (see Fig. 5A; Bosniak category 2). When any of the following features are present, further evaluation is warranted: aggressive calcifications (see Fig. 1C-E), abnormal density not fulfilling the criteria of a hyperdense cyst (see Figs. 3 and 4), or nodular septations (see Fig. 5B and C), or wall thickening (see Fig. 7; Bosniak) category 3). Small masses that cannot be characterized accurately also require further evaluation. Multiloculated masses(see Fig. 9) require surgery (Bosniak category 3). Most cases of multiple localized renal cysts can be distinguished from multiloculated masses and do not require surgery (see Fig. 10). Evaluation of cyst fluid by MR imaging has not been proved reliable in differentiating benign and malignant masses. MR imaging will become more useful when its spatial resolution equals that of CT. Masses that remain indeterminate after careful evaluation by ultrasonography and CT scanning can be evaluated additionally by angiography or cyst puncture. Management options for persistent enigmatic masses include follow-up radiologic studies, exploration, local excision, and nephrectomy.

Efficiency of acetylcholine receptor subunit assembly and its regulation by cAMP

Assembly of nicotinic acetylcholine receptor (AChR) subunits was investigated using mouse fibroblast cell lines stably expressing either Torpedo (All-11) or mouse (AM-4) alpha, beta, gamma, and delta AChR subunits. Both cell lines produce fully functional cell surface AChRs. We find that two independent treatments, lower temperature and increased intracellular cAMP can increase AChR expression by increasing the efficiency of subunit assembly. Previously, we showed that the rate of degradation of individual subunits was decreased as the temperature was lowered and that Torpedo AChR expression was acutely temperature sensitive, requiring temperatures lower than 37 degrees C. We find that Torpedo AChR assembly efficiency increases 56-fold as the temperature is decreased from 37 to 20 degrees C. To determine how much of this is a temperature effect on degradation, mouse AChR assembly efficiencies were determined and found to be only approximately fourfold more efficient at 20 than at 37 degrees C. With reduced temperatures, we can achieve assembly efficiencies of Torpedo AChR in fibroblasts of 20-35%. Mouse AChR in muscle cells is also approximately 30% and we obtain approximately 30% assembly efficiency of mouse AChR in fibroblasts (with reduced temperatures, this value approaches 100%). Forskolin, an agent which increases intracellular cAMP levels, increased subunit assembly efficiencies twofold with a corresponding increase in cell surface AChR. Pulse-chase experiments and immunofluorescence microscopy indicate that oligomer assembly occurs in the ER and that AChR oligomers remain in the ER until released to the cell surface. Once released, AChRs move rapidly through the Golgi membrane to the plasma membrane. Forskolin does not alter the intracellular distribution of AChR. Our results indicate that cell surface expression of AChR can be regulated at the level of subunit assembly and suggest a mechanism for the cAMP-induced increase in AChR expression.

From the Archives of the AFIP. Xanthogranulomatous pyelonephritis

Xanthogranulomatous pyelonephritis is a form of chronic infection of the kidney and surrounding tissues characterized by destruction and replacement of renal parenchyma by lipid-laden macrophages. Gross pathologic features include massive renal enlargement, lithiasis, peripelvic fibrosis, hydronephrosis, and lobulated yellow masses replacing renal parenchyma. Typically, the disease is diffuse and has characteristic imaging features. Less commonly, the process is focal and is difficult to differentiate from malignant disease on radiologic studies. Ultrasound demonstrates renal enlargement with multiple anechoic or hypoechoic masses replacing the normal corticomedullary differentiation and a contracted pelvis. Peripelvic fibrosis may obscure acoustic shadowing from a central staghorn calculus. On computed tomographic scans, a staghorn calculus may be seen in a contracted renal pelvis of an enlarged kidney, with characteristic low-attenuation, peripherally enhancing rounded masses. Extrarenal extension of the inflammatory process is frequently seen.

Cysts and cystic neoplasms

An overview of the various cystic neoplasms affecting the kidney is presented. Processes varying from a simple cyst to a cystic neoplasm will be reviewed discussing both their pathologic and imaging criteria.

Retroperitoneal tumors and lymphadenopathy

The retroperitoneum is the space between the parietal peritoneum anteriorly and the transversalis fascia posteriorly. Most retroperitoneal tumors arise from mesenchyme, neurogenic tissue, or embryonic rests. By this definition and by including lymph nodes as a retroperitoneal organ, lymphoma is not considered a primary retroperitoneal tumor.

Extraadrenal retroperitoneal paraganglioma: clinical, pathologic, and CT findings

Paragangliomas of the retroperitoneum arise from specialized neural crest cells distributed along the aorta in association with the sympathetic chain. In order to ascertain characteristic CT features of extraadrenal retroperitoneal paragangliomas to differentiate them from other retroperitoneal tumors, 31 discrete tumors and two cases of paragangliomatosis in 28 patients were reviewed retrospectively, and the CT features were correlated with clinical and pathologic findings. There were 16 men and 12 women. Average age was 37 years (range, 11-70 years). Twenty-four patients (86%) had hypertension. Of these, catecholamine levels were elevated in all 18 patients who had biochemical studies. Four patients (14%) had malignant paragangliomas. The discrete tumors were classified by location as suprarenal (26%), renal hilar (32%), or infrarenal (42%). Suprarenal paragangliomas could not be distinguished from the ipsilateral adrenal gland on CT. The average size of functional tumors was smaller (7.0 cm) than that of nonfunctional tumors (12.0 cm), but the sizes of the two groups overlapped. Smaller tumors were more likely to be homogeneous and have well-defined margins than were larger tumors. Our findings indicate that extraadrenal retroperitoneal paragangliomas are functionally active more often than previously reported and that they are readily detected by CT as soft-tissue masses closely associated with the entire length of the abdominal aorta. However, no CT feature was found that was unique for paraganglioma.

Lymphangioma of the retroperitoneum: CT and sonographic characteristic

The authors retrospectively evaluated radiologic, clinical, and pathologic findings in 19 cases of lymphangioma of the retroperitoneum. The tumors were judged confined to one compartment of the retroperitoneum in 68% of the cases, whereas in 32% of cases the tumor involved more than one compartment. Abdominal radiography depicted the mass in all cases. Excretory urography demonstrated organ displacement without tumor invasion in all cases. Sonography showed multiloculated fluid in 61% of cases and a unicameral mass in 39% of cases. All but one of the multiloculated lymphangiomas had thick septa. Sonography also depicted the fluid as uncomplicated in 56% of cases. The remainder had debris that sometimes layered in the dependent portion of the cyst. Computed tomography (CT) showed a unicameral mass in 57% and a septated mass in 43% of cases. CT also showed thin, smooth walls in 79% and thick, irregular walls in 21% of cases. At CT the fluid contents were found to be homogeneous and of fluid attenuation in 64% and were complex in 36% of cases. The attenuation of fluid in one case was the same as that of retroperitoneal fat. In two cases the mass contained mural calcification. The most characteristic radiologic finding of lymphangioma of the retroperitoneum is an elongated tumor containing uncomplicated fluid with or without septa. Chyle and mural calcification are very uncommon in this location.

Coexpression of two distinct muscle acetylcholine receptor alpha-subunits during development

The nicotinic acetylcholine receptor is a ligand-gated channel that mediates signalling at the vertebrate neuromuscular junction. It is a pentameric complex of four different subunits, assembled with a stoichiometry of alpha 2 beta gamma delta. Muscle-like alpha-subunits have been cloned from Torpedo, mouse, calf, rat, chicken, human and Xenopus, and only a single alpha-subunit complementary DNA from each species has been detected. We report here the cloning and characterization of a second muscle alpha-subunit cDNA from Xenopus, and show that this and a previously reported Xenopus alpha-subunit cDNA are encoded by distinct genes. The novel alpha-subunit reported here is expressed uniquely in oocytes; but both types of alpha-subunit are coexpressed throughout muscle development. This latter observation indicates that the expression of these two alpha-subunits is different from a previously reported developmental 'subunit-switch' mechanism used to generate channel diversity.

Coexpression of two distinct muscle acetylcholine receptor alpha-subunits during development

The nicotinic acetylcholine receptor is a ligand-gated channel that mediates signalling at the vertebrate neuromuscular junction. It is a pentameric complex of four different subunits, assembled with a stoichiometry of alpha 2 beta gamma delta. Muscle-like alpha-subunits have been cloned from Torpedo, mouse, calf, rat, chicken, human and Xenopus, and only a single alpha-subunit complementary DNA from each species has been detected. We report here the cloning and characterization of a second muscle alpha-subunit cDNA from Xenopus, and show that this and a previously reported Xenopus alpha-subunit cDNA are encoded by distinct genes. The novel alpha-subunit reported here is expressed uniquely in oocytes; but both types of alpha-subunit are coexpressed throughout muscle development. This latter observation indicates that the expression of these two alpha-subunits is different from a previously reported developmental 'subunit-switch' mechanism used to generate channel diversity.

Mature teratoma of the retroperitoneum: radiologic, pathologic, and clinical correlation

The authors retrospectively evaluated radiologic, clinical, and pathologic findings in 23 cases of mature teratoma arising within peri- or pararenal spaces. Radiologic studies--including abdominal radiographs (21 cases), excretory urograms (12 cases), sonograms (17 cases), and computed tomographic (CT) scans (18 cases)--were evaluated for tumor location, mass effect, calcification, fat, tumor invasion, echo pattern, and tissue characteristics. Most patients were female (3.4:1), younger than 6 months (50%), and asymptomatic. Abdominal radiography demonstrated a mass in 95%, calcium in 92%, and fat in 60% of cases in which CT revealed these components. Similarly, sonography showed uncomplicated fluid in 76% and calcium in 50% of cases. Fat was not reliably distinguished from other soft-tissue components on sonograms. The most characteristic radiologic findings of mature teratoma of the retroperitoneum are a complex mass containing a well-circumscribed fluid component of variable volume, adipose tissue and/or sebum in the form of a fat-fluid level, and calcification in either a congealed or linear strand pattern. These findings are better demonstrated by CT than by sonography.

Fibroblasts transfected with Torpedo acetylcholine receptor beta-, gamma-, and delta-subunit cDNAs express functional receptors when infected with a retroviral alpha recombinant

Torpedo californica acetylcholine receptor (AChR) alpha-, beta-, gamma-, and delta-subunit cDNAs were each stably introduced into muscle and/or fibroblast cell lines using recombinant retroviral vectors and viral infection, or using SV-40 vectors and DNA-mediated cotransfection. The expressed proteins were characterized in terms of their molecular mass, antigenicity, posttranslational processing, cell surface expression, stability in fibroblasts, stability in differentiated and undifferentiated muscle cells, and ability (of alpha) to bind alpha-bungarotoxin (BuTx). We demonstrated that the alpha, beta, gamma, and delta polypeptides acquired one, one, two, and three units of oligosaccharide, respectively. If all four subunits were expressed in the same cell, fully functional cell surface AChRs were produced which had a Kd for BuTx of 7.8 X 10(-11) M. In contrast, subunits expressed individually were not detected on the surface of fibroblasts and the Kd for BuTx binding to individual alpha polypeptides was only approximately 4 X 10(-7) M. The half-lives of the alpha, gamma, and delta subunits at 37 degrees C were all found to be quite short (approximately 43 min), while the half-life of the beta subunit was found to be even shorter (approximately 12 min). The unique half-life of the beta subunit suggests that it might perform a key regulatory role in the process of AChR subunit assembly. One stable fibroblast cell line was established by transfection that expressed beta, gamma, and delta subunits simultaneously. When this cell line was infected with a retroviral alpha recombinant, fully functional cell surface AChRs were produced. The successful expression of this pentameric protein complex combining transfection and infection techniques demonstrates one strategy for stably introducing the genes of a heterologous multisubunit protein complex into cells.

Neonatal ovarian cysts: sonographic-pathologic correlation

The authors reviewed the prenatal (11 infants) and postnatal (17 infants) sonograms and the clinical, surgical, and pathologic findings in 17 infants with an ovarian cyst to determine the sonographic features and natural history of neonatal ovarian cysts. An uncomplicated cyst (nontwisted, nonhemorrhagic) was completely anechoic and the cyst wall was imperceptible with sonography (five cases). A twisted or hemorrhagic cyst was cystic with a fluid-debris level, cystic with a retracting clot, septated with or without internal echoes, or solid (12 cases). These complicated cysts contained liquid and/or organized hematoma. Eleven of the 12 complicated cysts had a thin, highly echogenic wall. Cyst torsion commonly occurred in utero and could be diagnosed on prenatal sonograms by a typical sonographic appearance (eight cases). All of these infants were asymptomatic after birth. Four infants with hemorrhagic or twisted cysts were symptomatic. All cysts except one that resolved spontaneously were treated surgically, including three twisted cysts that showed no change in size over a 1-8-month interval. All of the cysts were of follicular origin.

Infiltrative renal lesions: CT-sonographic-pathologic correlation

The CT and sonographic findings in 23 cases of renal lesions in which the abnormality was infiltrative, as opposed to expansile, were analyzed (invasive transitional cell carcinoma [seven], renal lymphoma [six], metastasis to the kidney [three], acute bacterial nephritis [three], mesoblastic nephroma [two], squamous cell carcinoma of the renal pelvis [one], and renal cell carcinoma [one]). CT scans were evaluated for shape and density of the mass, pelvocaliceal displacement, effect on the renal sinus fat, and the presence of perirenal involvement. Sonograms were evaluated for the shape and echogenicity of the mass and for the effect on the renal sinus echoes. Findings of infiltrative growth included poorly defined margins of the mass; trapped, nondisplaced infundibulae; and calices with occasional calicectasis, diminished contrast enhancement, occasional nephrographic striations, replacement of central sinus fat, loss of central sinus echoes, and variable renal parenchymal echogenicity. The reniform shape was usually preserved and was present in 19 of 20 cases with CT and 13 of 15 cases with sonograms. These observations indicate that analyses of the margins, architecture, and effects on the collecting system and renal sinus by the mass are helpful in the diagnosis of those diseases that characteristically infiltrate the kidney.

Genetic reconstitution of functional acetylcholine receptor channels in mouse fibroblasts

Foreign genes can be stably integrated into the genome of a cell by means of DNA-mediated gene transfer techniques, and large quantities of homogenous cells that continuously express these gene products can then be isolated. Such an expression system can be used to study the functional consequences of introducing specific mutations into genes and to study the expressed protein in the absence of cellular components with which it is normally in contact. All four Torpedo acetylcholine receptor (AChR) subunit complementary DNA's were introduced into the genome of a mouse fibroblast cell by DNA-mediated gene transfer. A clonal cell line that stably produced high concentrations of correctly assembled cell surface AChR's and formed proper ligand-gated ion channels was isolated. With this new expression system, recombinant DNA, biochemical, pharmacological, and electrophysiological techniques were combined to study Torpedo AChR's in a single intact system. The physiological and pharmacological profiles of Torpedo AChR's expressed in mouse fibroblast cells differ in some details from those described earlier, and may provide a more accurate reflection of the properties of this receptor in its natural environment.

Multicystic dysplasia and crossed renal ectopia

Multicystic renal dysplasia in a crossed fused or nonfused ectopic kidney is a rare occurrence that produces unusual imaging findings. In four such cases in neonates, three presented with a palpable abdominal mass and one was discovered in utero with maternal sonography. In three cases, sonography showed a multicystic mass, contiguous with the lower pole of the orthotopic kidney. In the fourth infant, a crossed, tiny dysplastic kidney was not visualized, but its markedly dilated ectopic ureter was seen traversing the spine on CT. Ureteropelvic junction obstruction was present in the three fused orthotopic kidneys. The characteristic imaging findings of multicystic dysplasia and crossed renal ectopia include a multicystic mass of variable size that is contiguous with the lower pole of a hydronephrotic, malrotated kidney; ureteral displacement and/or dilatation; and contralateral absence of the kidney and its renal artery.

Primary adrenocortical carcinoma: sonographic evaluation with clinical and pathologic correlation in 26 patients

The sonograms of 26 patients (19 adults and seven children) with pathologically proven diagnoses of primary adrenocortical carcinoma were evaluated. Clinical corroboration was obtained in all cases. The size of the lesions ranged from 3 to 22 cm. The five smaller lesions (3-6 cm) showed a homogeneous echo pattern, similar to renal cortical echogenicity. The 21 larger lesions varied in echo texture, having a heterogeneous appearance with focal or scattered echopenic or echogenic zones representing areas of tumor necrosis, hemorrhage, and/or, rarely (19%), calcification. Even the largest lesions were fairly well delineated, often with a lobulated border. Few (7/26 or 27%) showed a surrounding echogenic thin capsulelike rim. All five small lesions showed clinical evidence of endocrine activity. Larger lesions were hormonally active less often (9/21 or 43%). Twelve patients (46%) showed no sign of endocrine activity and presented with symptoms such as fever, weight loss, abdominal discomfort, abdominal mass, hematuria, and hypertension. In the pediatric and adolescent age group (0-16 years), all tumors were hormonally active, while only seven (37%) of tumors in the adult population (17-69 years) were hormonally active. Unfortunately no echo pattern was characteristic enough to allow differentiation of adrenal adenoma from carcinoma. Smaller lesions are more likely to be benign, and larger lesions with areas of necrosis, hemorrhage, and calcification are more likely to be malignant.