Showing papers by "St. Jude Children's Research Hospital published in 1994"

Fusion of a Kinase Gene, ALK, to a Nucleolar Protein Gene, NPM, in Non-Hodgkin's Lymphoma

Abstract: The 2;5 chromosomal translocation occurs in most anaplastic large-cell non-Hodgkin's lymphomas arising from activated T lymphocytes. This rearrangement was shown to fuse the NPM nucleolar phosphoprotein gene on chromosome 5q35 to a previously unidentified protein tyrosine kinase gene, ALK, on chromosome 2p23. In the predicted hybrid protein, the amino terminus of nucleophosmin (NPM) is linked to the catalytic domain of anaplastic lymphoma kinase (ALK). Expressed in the small intestine, testis, and brain but not in normal lymphoid cells, ALK shows greatest sequence similarity to the insulin receptor subfamily of kinases. Unscheduled expression of the truncated ALK may contribute to malignant transformation in these lymphomas.

Association and activation of Jak-Tyk kinases by CNTF-LIF-OSM-IL-6 beta receptor components.

Abstract: A recently defined family of cytokines, consisting of ciliary neurotrophic factor (CNTF), leukemia inhibitory factor (LIF), oncostatin M (OSM), and interleukin-6 (IL-6), utilize the Jak-Tyk family of cytoplasmic tyrosine kinases. The beta receptor components for this cytokine family, gp130 and LIF receptor beta, constitutively associate with Jak-Tyk kinases. Activation of these kinases occurs as a result of ligand-induced dimerization of the receptor beta components. Unlike other cytokine receptors studied to date, the receptors for the CNTF cytokine family utilize all known members of the Jak-Tyk family, but induce distinct patterns of Jak-Tyk phosphorylation in different cell lines.

Interaction of IL-2R beta and gamma c chains with Jak1 and Jak3 : implications for XSCID and XCID

Abstract: Interleukin-2 (IL-2) signaling requires the dimerization of the IL-2 receptor beta.(IL-2R beta) and common gamma (gamma c) chains. Mutations of gamma c can result in X-linked severe combined immunodeficiency (XSCID). IL-2, IL-4, IL-7 (whose receptors are known to contain gamma c), and IL-9 (whose receptor is shown here to contain gamma c) induced the tyrosine phosphorylation and activation of the Janus family tyrosine kinases Jak1 and Jak3. Jak1 and Jak3 associated with IL-2R beta and gamma c, respectively; IL-2 induced Jak3-IL-2R beta and increased Jak3-gamma c associations. Truncations of gamma c, and a gamma c, point mutation causing moderate X-linked combined immunodeficiency (XCID), decreased gamma c-Jak3 association. Thus, gamma c mutations in at least some XSCID and XCID patients prevent normal Jak3 activation, suggesting that mutations of Jak3 may result in an XSCID-like phenotype.

Involvement of the Jak-3 Janus kinase in signalling by interleukins 2 and 4 in lymphoid and myeloid cells

Abstract: Many cytokines function through interaction with receptors of the cytokine receptor superfamily. Although lacking catalytic domains, cytokine receptors couple ligand binding to induction of protein tyrosine phosphorylation. Recent studies have shown that one or more of the Janus kinase family members (Jaks) associate with cytokine receptors and are tyrosine phosphorylated and activated following ligand binding. Here we describe a new Jak family kinase, Jak-3, and demonstrate that Jak-3, and to a lesser extent Jak-1, are tyrosine phosphorylated and Jak-3 is activated in the responses to interleukin-2 and interleukin-4 in T cells and myeloid cells. Jak-3 activation requires the serine-rich, membrane-proximal domain of the interleukin-2 receptor beta-chain, but does not require the acidic domain that is required for association and activation of Src family kinases.

Functional activation of Jak1 and Jak3 by selective association with IL-2 receptor subunits

Abstract: The interleukin-2 receptor (IL-2R) consists of three subunits: the IL-2R alpha, IL-2R beta, and IL-2R gamma chains, the last of which is also used in the receptors for IL-4, IL-7, and IL-9. Stimulation with IL-2 induces the tyrosine phosphorylation and activation of the Janus kinases Jak1 and Jak3. Jak1 and Jak3 were found to be selectively associated with the "serine-rich" region of IL-2R beta and the carboxyl-terminal region of IL-2R gamma, respectively. Both regions were necessary for IL-2 signaling. Furthermore, Jak3-negative fibroblasts expressing reconstituted IL-2R became responsive to IL-2 after the additional expression of Jak3 complementary DNA. Thus, activation of Jak1 and Jak3 may be a key event in IL-2 signaling.

Virus-specific CD8 + T-cell memory determined by clonal burst size

Abstract: Although some viruses, particularly the herpes viruses, may never be eliminated from the body, others like influenza A, regularly reinfect humans and boost waning crossreactive CD8+ T-cell immunity. Prolonged T-cell memory is found for viruses that are unlikely to be re-encountered and which do not persist in the host genome, indicating that CD8+ T-cell memory might be independent of continued (or sporadic) antigenic exposure. A feature of virus-specific CD8+ T-cell memory is that antigen-specific cytotoxic T-lymphocyte precursors (CTLp) are greatly increased and remain high throughout life. The idea that persistence of the inducing antigen is essential is based on experiments in which adoptively transferred CD8+ memory T cells could not be detected for more than a few weeks in naive recipient mice without secondary challenge. Here we show that restimulation of such chimaeric mice with an inducing Sendai virus antigen increases the clonal burst size more than 7-fold within 8 days, making memory CTLp easier to detect in the longer term. We find that Sendai-virus-specific CTLp are maintained for > 250 days in irradiated uninfected recipients, including reconstituted beta 2-microglobulin-/- mice. To determine whether a source of viral peptide can persist after primary infection, we gave Sendai-virus-specific Thy1.1+ memory spleen cells to naive mice that had been minimally depleted of Thy1.2+ T cells, or to comparable recipients that had recovered from infection with Sendai virus or influenza virus. Although antibody against Sendai virus was never found in the naive recipients, Sendai-virus-specific CD8+ memory T cells were maintained equally well in each case for > 100 days after cell transfer. We find no evidence for persisting depots of viral protein that might feed into the endogenous processing pathway and maintain virus-specific CD8+ T-cell memory.

Identification of a new catenin: the tyrosine kinase substrate p120cas associates with E-cadherin complexes.

Abstract: p120cas is a tyrosine kinase substrate implicated in ligand-induced receptor signaling through the epidermal growth factor, platelet-derived growth factor, and colony-stimulating factor receptors and in cell transformation by Src. Here we report that p120 associates with a complex containing E-cadherin, alpha-catenin, beta-catenin, and plakoglobin. Furthermore, p120 precisely colocalizes with E-cadherin and catenins in vivo in both normal and Src-transformed MDCK cells. Unlike beta-catenin and plakoglobin, p120 has at least four isoforms which are differentially expressed in a variety of cell types, suggesting novel means of modulating cadherin activities in cells. In Src-transformed MDCK cells, p120, beta-catenin, and plakoglobin were heavily phosphorylated on tyrosine, but the physical associations between these proteins were not disrupted. Association of p120 with the cadherin machinery indicates that both Src and receptor tyrosine kinases cross talk with proteins important for cadherin-mediated cell adhesion. These results also strongly suggest a role for p120 in cell adhesion.

JAK2 associates with the beta c chain of the receptor for granulocyte-macrophage colony-stimulating factor, and its activation requires the membrane-proximal region.

Abstract: The high-affinity receptor for granulocyte-macrophage colony-stimulating factor (GM-CSF) consists of a unique alpha chain and a beta c subunit that is shared with the receptors for interleukin-3 (IL-3) and IL-5. Two regions of the beta c chain have been defined; these include a membrane-proximal region of the cytoplasmic domain that is required for mitogenesis and a membrane-distal region that is required for activation of Ras, Raf-1, mitogen-activated protein kinase, and S6 kinase. Recent studies have implicated the cytoplasmic protein tyrosine kinase JAK2 in signalling through a number of the cytokine receptors, including the IL-3 and erythropoietin receptors. In the studies described here, we demonstrate that GM-CSF stimulation of cells induces the tyrosine phosphorylation of JAK2 and activates its in vitro kinase activity. Mutational analysis of the beta c chain demonstrates that only the membrane-proximal 62 amino acids of the cytosolic domain are required for JAK2 activation. Thus, JAK2 activation is correlated with induction of mitogenesis but does not, alone, activate the Ras pathway. Carboxyl truncations of the alpha chain, which inactivate the receptor for mitogenesis, are unable to mediate GM-CSF-induced JAK2 activation. Using baculovirus-expressed proteins, we further demonstrate that JAK2 physically associates with the beta c chain but not with the alpha chain. Together, the results further support the hypothesis that the JAK family of kinase are critical to coupling cytokine binding to tyrosine phosphorylation and ultimately mitogenesis.

A note on Gauss—Hermite quadrature

Abstract: SUMMARY For Gauss-Hermite quadrature, we consider a systematic method for transforming the variable of integration so that the integrand is sampled in an appropriate region. The effectiveness of the quadrature then depends on the ratio of the integrand to some Gaussian density being a smooth function, well approximated by a low-order polynomial. It is pointed out that, in this approach, order one Gauss-Hermite quadrature becomes the Laplace approximation. Thus the quadrature as implemented here can be thought of as a higher-order Laplace approximation.

Regulation of cyclin D-dependent kinase 4 (cdk4) by cdk4-activating kinase.

Abstract: The accumulation of assembled holoenzymes composed of regulatory D-type cyclins and their catalytic partner, cyclin-dependent kinase 4 (cdk4), is rate limiting for progression through the G1 phase of the cell cycle in mammalian fibroblasts. Both the synthesis and assembly of D-type cyclins and cdk4 depend upon serum stimulation, but even when both subunits are ectopically overproduced, they do not assemble into complexes in serum-deprived cells. When coexpressed from baculoviral vectors in intact Sf9 insect cells, cdk4 assembles with D-type cyclins to form active protein kinases. In contrast, recombinant D-type cyclin and cdk4 subunits produced in insect cells or in bacteria do not assemble as efficiently into functional holoenzymes when combined in vitro but can be activated in the presence of lysates obtained from proliferating mammalian cells. Assembly of cyclin D-cdk4 complexes in coinfected Sf9 cells facilitates phosphorylation of cdk4 on threonine 172 by a cdk-activating kinase (CAK). Assembly can proceed in the absence of this modification, but cdk4 mutants which cannot be phosphorylated by CAK remain catalytically inactive. Therefore, formation of the cyclin D-cdk4 complex and phosphorylation of the bound catalytic subunit are independently regulated, and in addition to the requirement for CAK activity, serum stimulation is required to promote assembly of the complexes in mammalian cells.

The clinicopathologic spectrum of putative extrarenal rhabdoid tumors. An analysis of 42 cases studied with immunohistochemistry or electron microscopy.

Abstract: The existence of extrarenal rhabdoid tumor (ERRT) as a discrete pathologic entity has been controversial despite frequent reports of its occurrence. We performed immunohistochemistry, electron microscopy, or both on 42 cases with this diagnosis sent in consultation to us. Only 12 of the 42 neoplasms had the histological findings of "classic" malignant rhabdoid tumor of the kidney; the remainder displayed a variety of neural, epithelial, myoid, mesenchymal, or ependymal patterns. Electron microscopy also showed that most possessed neural, epithelial, or ependymal features. Immunohistochemistry generally revealed marked polyphenotypia, with immunoreactivity to a wide array of antibodies against neural, epithelial, glial, and myogenic markers. A specific tissue-based diagnostic category could not be assigned in only 11 of the 42 cases, seven of which lacked material for a comprehensive ultrastructural or immunohistochemical study. We conclude that tumors currently diagnosed as ERRT represent a heterogeneous group of neoplasms that may form unique subsets of known entities within the specific site where they arise or that may defy classification into a specific alternative category. Our findings lead us to believe that the term ERRT is not valid as representing a specific diagnostic entity and to prefer the term "poorly differentiated neoplasm with rhabdoid features" for undifferentiated tumors.

Reverse genetics provides direct evidence for a correlation of hemagglutinin cleavability and virulence of an avian influenza A virus.

Abstract: To obtain direct evidence for a relationship between hemagglutinin (HA) cleavability and the virulence of avian influenza A viruses, we generated a series of HA cleavage mutants from a virulent virus, A/turkey/Ontario/7732/66 (H5N9), by reverse genetics. A transfectant virus containing the wild-type HA with R-R-R-K-K-R at the cleavage site, which was readily cleaved by endogenous proteases in chicken embryo fibroblasts (CEF), was highly virulent in intramuscularly or intranasally/orally inoculated chickens. By contrast, a mutant containing the HA with an avirulent-like sequence (R-E-T-R) at the cleavage site, which was not cleaved by the proteases in CEF, was avirulent in chickens, indicating that a genetic alteration confined to the HA cleavage site can affect cleavability and virulence. Mutant viruses with HA cleavage site sequences of T-R-R-K-K-R or T-T-R-K-K-R were as virulent as viruses with the wild-type HA, whereas a mutant with a two-amino-acid deletion but retention of four consecutive basic residues (R-K-K-R) was as avirulent as a virus with the avirulent-type HA. Interestingly, although a mutant containing an HA with R-R-R-K-T-R, which has reduced cleavability in CEF, was as virulent as viruses with high HA cleavability when given intramuscularly, it was less virulent when given intranasally/orally. We conclude that the degree of HA cleavability in CEF predicts the virulence of avian influenza viruses.

Thiopurine methyltransferase activity in American white subjects and black subjects

Abstract: Background Thiopurine methyltransferase (TPMT) is a cytoplasmic enzyme that preferentially catalyzes the S-methylation of aromatic and heterocyclic sulfhydryl compounds, including 6-mercaptopurine. TPMT exhibits genetic polymorphism in white populations, with 89% of individuals having high TPMT activity, 11% having intermediate activity, and one in 300 having extremely low or absent activity. TPMT activity is inversely correlated with formation of active 6-mercaptopurine metabolites (thioguanine nucleotides), thereby influencing 6-mercaptopurine toxicity and efficacy. Methods To investigate ethnic and gender differences in TPMT, we measured erythrocyte TPMT activity in 209 white healthy subjects and 196 black healthy subjects (202 women and 203 men). Results The black population had lower TPMT activity than the white population (median, 14.4 versus 16.8 units/ml packed erythrocytes; p < 0.001). Maximum likelihood estimation of TPMT activity distribution identified 91.9% and 93.9% with high activity and 7.7% and 6.1% with intermediate activity in the white and black groups, respectively. Conclusions These data indicate that TPMT activity is similarly polymorphic in American black subjects and white subjects, although median TPMT activity is approximately 17% lower in black subjects. Clinical Pharmacology and Therapeutics (1994) 55, 15–20; doi:10.1038/clpt.1994.4

Ornithine decarboxylase is a mediator of c-Myc-induced apoptosis.

Abstract: c-Myc plays a central role in the regulation of cell cycle progression, differentiation, and apoptosis. However, the proteins which mediate c-Myc function(s) remain to be determined. Enforced c-myc expression rapidly induces apoptosis in interleukin-3 (IL-3)-dependent 32D.3 murine myeloid cells following IL-3 withdrawal, and this is associated with the constitutive, growth factor-independent expression of ornithine decarboxylase (ODC), a rate-limiting enzyme of polyamine biosynthesis. Here we have examined the role of ODC in c-Myc-induced apoptosis. Enforced expression of ODC, like c-myc, is sufficient to induce accelerated death following IL-3 withdrawal. ODC induced cell death in a dose-dependent fashion, and alpha-difluoromethylornithine (DFMO), an irreversible inhibitor of ODC enzyme activity, effectively blocked ODC-induced cell death. ODC-induced cell death was due to the induction of apoptosis. We also demonstrate that ODC is a mediator of c-Myc-induced apoptosis. 32D.3-derived c-myc clones have augmented levels of ODC enzyme activity, and their rates of death were also a function of their ODC enzyme levels. Importantly, the rates of death of c-myc clones were inhibited by treatment with DFMO. These findings demonstrate that ODC is an important mediator of c-Myc-induced apoptosis and suggest that ODC mediates other c-Myc functions.

Stat4, a novel gamma interferon activation site-binding protein expressed in early myeloid differentiation.

Abstract: Interferon regulation of gene expression is dependent on the tyrosine phosphorylation and activation of the DNA-binding activity of two related proteins of 91 kDa (STAT1) and/or 113 kDa (STAT2). Recent studies have suggested that these proteins are substrates of Janus kinases and that proteins related in STAT1 are involved in a number of signalling pathways, including those activated in myeloid cells by erythropoietin and interleukin-3 (IL-3). To clone STAT-related proteins from myeloid cells, degenerate oligonucleotides were used in PCRs to identify novel family members expressed in myeloid cells. This approach allowed the identification and cloning of the Stat4 gene, which is 52% identical to STAT1. Unlike STAT1, Stat4 expression is restricted but includes myeloid cells and spermatogonia. In the erythroid lineage, Stat4 expression is differentially regulated during differentiation. Functionally, Stat4 has the properties of other STAT family genes. In particular, cotransfection of expression constructs for Stat4 and Jak1 and Jak2 results in the tyrosine phosphorylation of Stat4 and the acquisition of the ability to bind to the gamma interferon (IFN-gamma)-activated sequence of the interferon regulatory factor 1 (IRF-1) gene. Stat4 is located on mouse chromosome 1 and is tightly linked to the Stat1 gene, suggesting that the genes arose by gene duplication. Unlike Stat1, neither IFN-alpha nor IFN-gamma activates Stat4. Nor is Stat4 activated in myeloid cells by a number of cytokines, including erythropoietin, IL-3, granulocyte colony-stimulating factor, stem cell factor, colon-stimulating factor 1, hepatocyte growth factor, IL-2, IL-4, and IL-6.

Proprotein-processing endoproteases PC6 and furin both activate hemagglutinin of virulent avian influenza viruses.

Abstract: Among the proprotein-processing subtilisin-related endoproteases, furin has been a leading candidate for the enzyme that activates the hemagglutinin (HA) of virulent avian influenza viruses. In the present study, we examined the cleavage activity of two other recently isolated ubiquitous subtilisin-related proteases, PACE4 and PC6, using wild-type HA of A/turkey/Ireland/1378/83 (H5N8) and a series of its mutant HAs. Vaccinia virus-expressed wild-type HA was not cleaved in human colon adenocarcinoma LoVo cells, which lack active furin. This processing defect was corrected by the expression of furin and PC6 but not of PACE4 and a control wild-type vaccinia virus. PC6 showed a sequence specificity similar to that with the endogenous proteases in cultured cells. When LoVo cells were infected with a virulent avian virus, A/turkey/Ontario/7732/66 (H5N9), only noninfectious virions were produced because of the lack of HA cleavage. However, when the cells were coinfected with vaccinia virus that expressed either furin or PC6, the avian virus underwent multiple cycles of replication, indicating that both furin and PC6 specifically cleave the virulent virus HA at the authentic site. These data suggest that PC6, as well as furin, can activate virulent avian influenza viruses in vivo, implying the presence of multiple HA cleavage enzymes in animals.

Activation of cyclin-dependent kinase 4 (cdk4) by mouse MO15-associated kinase.

Abstract: The assembly of functional holoenzymes composed of regulatory D-type cyclins and cyclin-dependent kinases (cdks) is rate limiting for progression through the G1 phase of the mammalian somatic cell cycle. Complexes between D-type cyclins and their major catalytic subunit, cdk4, are catalytically inactive until cyclin-bound cdk4 undergoes phosphorylation on a single threonyl residue (Thr-172). This step is catalyzed by a cdk-activating kinase (CAK) functionally analogous to the enzyme which phosphorylates cdc2 and cdk2 at Thr-161/160. Here, we demonstrate that the catalytic subunit of mouse cdc2/cdk2 CAK (a 39-kDa protein designated p39MO15) can assemble with a regulatory protein present in either insect or mammalian cells to generate a CAK activity capable of phosphorylating and enzymatically activating both cdk2 and cdk4 in complexes with their respective cyclin partners. A newly identified 37-kDa cyclin-like protein (cyclin H [R. P. Fisher and D. O. Morgan, Cell 78:713-724, 1994]) can assemble with p39MO15 to activate both cyclin A-cdk2 and cyclin D-cdk4 in vitro, implying that CAK is structurally reminiscent of cyclin-cdk complexes themselves. Antisera produced to the p39MO15 subunit can completely deplete mammalian cell lysates of CAK activity for both cyclin A-cdk2 and cyclin D-cdk4, with recovery of activity in the resulting immune complexes. By using an immune complex CAK assay, CAK activity for cyclin A-cdk2 and cyclin D-cdk4 was detected both in quiescent cells and invariantly throughout the cell cycle. Therefore, although it is essential for the enzymatic activation of cyclin-cdk complexes, CAK appears to be neither rate limiting for the emergence of cells from quiescence nor subject to upstream regulatory control by stimulatory mitogens.

11q23/MLL rearrangement confers a poor prognosis in infants with acute lymphoblastic leukemia

Abstract: PURPOSELeukemic cell characteristics were analyzed in infants less than 1 year of age with acute lymphoblastic leukemia (ALL) to determine adverse prognostic factors that might explain the poor prognosis of this group.PATIENTS AND METHODSTreatment outcomes were analyzed according to the presenting clinical and laboratory features of 30 infants treated between May 1979 and April 1993. A stepwise multivariate regression model was used to identify the most important prognostic indicator with respect to event-free survival.RESULTSInfant ALL cases were characterized by high presenting leukocyte count (median, 87 x 10(9)/L), increased frequency of CNS leukemia (50%), and blast cells with a CD10- phenotype (67%), myeloid-associated antigen expression (48%), and 11q23/MLL rearrangement (68%). The 11q23/MLL involvement was correlated with age less than 6 months, CD10- phenotype, myeloid-associated antigen expression, and high leukocyte count. Although 11q23/MLL involvement, age less than 6 months, myeloid-associat...

Patient characteristics associated with high-risk methotrexate concentrations and toxicity.

Abstract: PURPOSEFollowing high-dose methotrexate (HD-MTX) treatment, delayed MTX elimination is an important problem because it necessitates increased leucovorin rescue and additional hospitalization for hydration and urinary alkalinization. Our purpose was to identify factors associated with high-risk MTX plasma concentrations (defined by plasma concentration > or = 1.0 mumol/L at 42 hours from the start of MTX) and with toxicity.PATIENTS AND METHODSVariables associated with MTX concentrations and toxicity were assessed in 134 children treated with one to five courses of HD-MTX (900 to 3,700 mg/m2 intravenously [i.v.] over 24 hours for a total of 481 courses) for acute lymphoblastic leukemia (ALL).RESULTSHigh-risk MTX concentrations, toxicity (usually mild mucositis), and delay in resuming continuation chemotherapy occurred in 106 (22%), 123 (26%), and 66 (14%) of 481 courses, respectively. Using a mixed effects model for repeated measures, high-risk MTX concentrations were significantly associated with a higher ...

Blast cell methotrexate-polyglutamate accumulation in vivo differs by lineage, ploidy, and methotrexate dose in acute lymphoblastic leukemia.

Abstract: High-dose methotrexate (HDMTX) is a component of most treatment protocols for childhood acute lymphoblastic leukemia (ALL), yet recent studies of receptor-mediated transport and saturable polyglutamylation have questioned its rationale. To investigate this in vivo, methotrexate and its active polyglutamated metabolites (MTX-PG) were measured in bone marrow blasts obtained from 101 children randomized to single-agent therapy with either HDMTX (1 g/m2 per 24 h i.v., n = 47) or low-dose MTX (LDMTX, 30 mg/m2 by mouth every 6 h x 6, n = 54), before remission induction therapy. Blast concentrations of total MTX-PGs (median 460 vs 1380 pmol/10(9) cells) and of long-chain MTX-glu4-6 were both significantly higher after HDMTX (P nonhyperdiploid), and percentage S-phase. This is the first evidence that HDMTX achieves higher MTX-PG concentrations in ALL blasts in vivo, establishing a rationale for HDMTX in the treatment of childhood ALL, especially T-lineage or nonhyperdiploid B-lineage ALL, disease characteristics associated with a poor prognosis on conventional therapy.

Granulocytic sarcoma in childhood leukemia: imaging features.

Abstract: PURPOSE: To assess imaging features of granulocytic sarcoma (GS) in children with myelogenous leukemia. MATERIALS AND METHODS: Retrospectively analyzed were radiographs, bone scintigrams, ultrasound (US) scans, computed tomography (CT) scans, and magnetic resonance (MR) images obtained in 30 patients with acute and one with chronic myelogenous leukemia. RESULTS: With one exception in which GS antedated leukemia, GS was present concurrently with onset of leukemia or during remission or relapse. Radiographs, nuclear studies, and US findings were nonspecific. One parascapular GS was hyperintense on T2-weighted MR images, but in all eight central nervous system studies, tumors were isointense to gray matter, muscle, or marrow on T1-weighted images and to white matter or muscle, marrow, or both on T2-weighted images. Contrast enhancement of GS was homogenous on cranial CT scans and all MR studies. CONCLUSION: CT and MR imaging features may allow distinction of GS from hematomas and abscesses, which are also co...