Effective One-Dimensional Coupling in the Highly Frustrated Square-Lattice Itinerant Magnet CaCo_{2-y}As_{2}.

Inelastic neutron scattering measurements on the itinerant antiferromagnet CaCo_{2-y}As_{2} at a temperature of 8 K reveal two orthogonal planes of scattering perpendicular to the Co square lattice in reciprocal space, demonstrating the presence of effective one-dimensional spin interactions. These results are shown to arise from near-perfect bond frustration within the J_{1}-J_{2} Heisenberg model on a square lattice with ferromagnetic J_{1} and hence indicate that the extensive previous experimental and theoretical study of the J_{1}-J_{2} Heisenberg model on local-moment square spin lattices should be expanded to include itinerant spin systems.

Ba(1-x)K(x)Mn2As2: an antiferromagnetic local-moment metal.

The compound BaMn2As2 with the tetragonal ThCr2Si2 structure is a local-moment antiferromagnetic insulator with a Néel temperature T(N)=625 K and a large ordered moment µ=3.9µ(B)/Mn. We demonstrate that this compound can be driven metallic by partial substitution of Ba by K while retaining the same crystal and antiferromagnetic structures together with nearly the same high T(N) and large µ. Ba(1-x)K(x)Mn2As2 is thus the first metallic ThCr2Si2-type MAs-based system containing local 3d transition metal M magnetic moments, with consequences for the ongoing debate about the local-moment versus itinerant pictures of the FeAs-based superconductors and parent compounds. The Ba(1-x)K(x)Mn2As2 class of compounds also forms a bridge between the layered iron pnictides and cuprates and may be useful to test theories of high T(c) superconductivity.

Endoscopic management of a rare case of nasal glioma in Meckel's cave in an adult: case report.

BACKGROUND: Nasal glioma or glial heterotopia is a rare embryologic anomaly that heralds its presence shortly after birth or in childhood. Nasal glioma in an adult is very rare, often asymptomatic and the occurrence of nasal glioma in Meckel's cave in an adult has not been previously reported. CASE REPORT: The authors encountered a case of an incidentally diagnosed Meckel's cave nasal glioma in a 40-year-old male which was successfully excised by an endonasal endoscopic transmaxillary transpterygoid approach. CONCLUSION: The occurrence of a nasal glioma in Meckel's cave an adult is very rare. Considering the deep skull base location, endonasal endoscopic surgery provides a minimal access technique to reach this location with excellent results.

Kondo lattice heavy fermion behavior in CeRh2Ga2.

The physical properties of an intermetallic compound CeRh2Ga2 have been investigated by magnetic susceptibility [Formula: see text], isothermal magnetization M(H), heat capacity [Formula: see text], electrical resistivity [Formula: see text], thermal conductivity [Formula: see text] and thermopower S(T) measurements. CeRh2Ga2 is found to crystallize with CaBe2Ge2-type primitive tetragonal structure (space group P4/nmm). No evidence of long range magnetic order is seen down to 1.8 K. The [Formula: see text] data show paramagnetic behavior with an effective moment [Formula: see text]/Ce indicating Ce3+ valence state of Ce ions. The [Formula: see text] data exhibit Kondo lattice behavior with a metallic ground state. The low-T [Formula: see text] data yield an enhanced Sommerfeld coefficient [Formula: see text] mJ/mol K2 characterizing CeRh2Ga2 as a moderate heavy fermion system. The high-T [Formula: see text] and [Formula: see text] show an anomaly near 255 K, reflecting a phase transition. The [Formula: see text] suggests phonon dominated thermal transport with considerably higher values of Lorenz number L(T) compared to the theoretical Sommerfeld value L 0.

Investigations of the effect of nonmagnetic Ca substitution for magnetic Dy on spin-freezing in Dy2Ti2O7.

Physical properties of partially Ca substituted hole-doped Dy2Ti2O7 have been investigated by ac magnetic susceptibility χ(ac)(T), dc magnetic susceptibility χ(T), isothermal magnetization M(H) and heat capacity C(p)(T) measurements on Dy1.8Ca0.2Ti2O7. The spin-ice system Dy2Ti2O7 exhibits a spin-glass type freezing behavior near 16 K. Our frequency dependent χ(ac)(T) data of Dy1.8Ca0.2Ti2O7 show that the spin-freezing behavior is significantly influenced by Ca substitution. The effect of partial nonmagnetic Ca(2+) substitution for magnetic Dy(3+) is similar to the previous study on nonmagnetic isovalent Y(3+) substituted Dy(2-x)Y(x) Ti2O7 (for low levels of dilution), however the suppression of spin-freezing behavior is substantially stronger for Ca than Y. The Cole-Cole plot analysis reveals semicircular character and a single relaxation mode in Dy1.8Ca0.2Ti2O7 as for Dy2Ti2O7. No noticeable change in the insulating behavior of Dy2Ti2O7 results from the holes produced by 10% Ca(2+) substitution for Dy(3+) ions.

The magnetic structure of EuCu2Sb2.

Antiferromagnetic ordering of EuCu2Sb2 which forms in the tetragonal CaBe2Ge2-type structure (space group P4/nmm #129) has been studied using neutron powder diffraction and (151)Eu Mössbauer spectroscopy. The room temperature (151)Eu isomer shift of -12.8(1) mm s(-1) shows the Eu to be divalent, while the (151)Eu hyperfine magnetic field (B(hf)) reaches 28.7(2) T at 2.1 K, indicating a full Eu(2+) magnetic moment. B(hf)(T) follows a smooth S = 7/2 Brillouin function and yields an ordering temperature of 5.1(1) K. Refinement of the neutron diffraction data reveals a collinear A-type antiferromagnetic arrangement with the Eu moments perpendicular to the tetragonal c-axis. The refined Eu magnetic moment at 0.4 K is 7.08(15) µ(B) which is the full free-ion moment expected for the Eu(2+) ion with S = 7/2 and a spectroscopic splitting factor of g = 2.

Muon spin relaxation study on itinerant ferromagnet CeCrGe3 and the effect of Ti substitution on magnetism of CeCrGe3.

A Muon spin relaxation (µSR) study has been performed on the Kondo lattice heavy fermion itinerant ferromagnet CeCrGe3. Recent investigations of bulk properties have revealed a long-range ordering of Cr moments at Tc = 70 K in this compound. Our µSR investigation between 1.2 K and 125 K confirm the bulk magnetic order which is marked by a loss in initial asymmetry below 70 K accompanied with a sharp increase in the muon depolarization rate. Field dependent µSR spectra show that the internal field at the muon site is higher than 0.25 T apparently due to the ferromagnetic nature of ordering. The effect of Ti substitution on the magnetism in CeCrGe3 is presented. A systematic study has been made on polycrystalline CeCr(1-x)Ti(x)Ge3 (0 ⩽ x ⩽ 1) using magnetic susceptibility χ(T), isothermal magnetization M(H), specific heat C(T) and electrical resistivity ρ(T) measurements which clearly reveal that the substitution of Ti for Cr in CeCrGe3 strongly influences the exchange interaction and ferromagnetic ordering of Cr moments. The Cr moment ordering temperature is suppressed gradually with increasing Ti concentration up to x = 0.50 showing Tc = 7 K beyond which Ce moment ordering starts to dominate and a crossover between Cr and Ce moment ordering is observed with a Ce moment ordering Tc = 14 K for x = 1.0. The Kondo lattice behavior is evident from temperature dependence of ρ(T) in all CeCr(1-x)Ti(x)Ge3 samples.

Zygomatic approach to skull-base lesions.

A modification of the preauricular skull-base approach is described. After sectioning and downward displacement of the zygomatic arch, the coronoid process of the mandible is dissected and sectioned at its base. The temporal muscle, with its coronoid insertion, is then retracted upward. This approach provides direct and unobstructed access to the temporal and infratemporal fossae. Adequate vascularity of the temporal muscle is maintained. The exposure encompasses the internal carotid artery in the neck for vascular control. Extensive reconstruction is eliminated. The described technique was used in seven patients with lesions of the skull base. There was no operative mortality, and morbidity consisted of temporary restriction of mandibular opening in two patients.

Plasticity of the extracranial facial nerve.

Although the expansion properties of peripheral nerves have been a matter of considerable study in recent years, investigations of the plasticity of cranial nerves, including the facial nerve, have been lacking. Clinicians, however, have long recognized the tenacity of facial nerve function in patients with slow-growing benign tumors that enormously distort the nerve. An experimental study was designed to assess whether tissue expansion techniques can be applied to the extracranial portion of the facial nerves of cats. In eight cats the frontozygomatic branch of the facial nerve was expanded by stages in seven sessions over a period of 40 days. The length of the nerve increased an average of 95% without significantly impairing nerve function. Pressure changes in the expander averaged 75 mm Hg during each stage of expansion. Electroneurography was performed after each injection of the expander. Statistical analysis of these data did not show consistent evidence of demyelination or denervation, and all but one cat exhibited a normal blink reflex and had normal electromyographic findings at the end of the experiment. Histologic examination of the expanded nerves, however, did show inflammatory changes, intraneural edema, and occasional demyelination.

Sublabial surgical approach to the nasal cavity and paranasal sinuses.

A sublabial approach to the nasal cavity, paranasal sinuses and the nasopharynx degloving the middle third of the face has been described. Its major advantages over the other approaches have been compared and the usefulness of this approach has been stressed. The incidence of complications from this approach has been described and found to be acceptable.

Surgical considerations in tracheal stenosis.

From 1969 to 1990, 43 patients with tracheal stenosis were treated at the University of Mississippi Medical Center. Seventy-four percent of these patients (n = 32) had intrinsic tracheal stenosis, most frequently as a complication of prolonged endotracheal trauma. A total of 41 distinctly separate stenotic segments were identified in the 32 patients. The stenoses were considered moderate or severe in 33 (80%) of the 41 cases and the length of the stenotic segment was greater than 1 cm in 23 (56%) of the cases. An overall 70% success rate was achieved following 93 surgical procedures in this group. The concurrent presence of glottic/subglottic stenosis, multiple segments of stenosis, bilateral vocal cord paralysis, tracheoesophageal fistula, and a tendency to marked hypertrophic scar formation were found to be significant factors in the surgical management of this patient group.

Intracranial complications of mucormycosis: an experimental model and clinical review.

The clinical course of patients with mucormycosis of the paranasal sinuses can be unpredictable and is often determined by intrinsic host factors. The degree to and mechanism(s) by which these factors influence a patient's ability to survive the disease are poorly understood. Extensions to orbital and intracranial structures occur in some patients with paranasal sinus mucormycosis despite aggressive treatment. Controversies persist over adequate antifungal regimen, the precise role of hyperbaric oxygenation, and the appropriate extent of surgical debridement. We have developed an alloxan-induced immunocompromised murine model of mucormycosis in mice. Deferoxamine iron chelation produced rhinocerebral mucormycosis in these animals when challenged intraethmoidally with Rhizopus spores. The implications of our experimental studies in the content of our clinical experience in managing patients with intracranial extensions of paranasal sinus mucormycosis are discussed.

Magnetic resonance navigation for head and neck lesions.

OBJECTIVE: Review applications of interventional magnetic resonance imaging and describe methods, procedures, and additional instrumentation for the magnetic resonance "operating theater." Describe advantages of magnetic resonance navigation for biopsies of head and neck tumors. STUDY DESIGN: Patients with palpable and nonpalpable head and neck and cranial base tumors were recruited into the study. Patients underwent magnetic resonance-guided biopsy. Retrospective analysis of 21 patients was conducted. METHODS: 0.5 Tesla superconducting open magnetic resonance imaging was used for navigation of the biopsy needle. Patient records and magnetic resonance images were reviewed. The type, size, and location of the lesions were tabulated. Type of anesthesia and monitoring method were analyzed. The histopathologic correlation was conducted in patients who required further surgeries or open surgical biopsies. RESULTS: Twenty-two biopsies were carried out in the magnetic resonance suite. One patient required general anesthesia and the other biopsies were conducted under intravenous sedation. There was only one case of nonconcurrence in a patient with Wegener's granulomatosis of the posterior orbit. Overall, a 92% concurrence rate between image-directed fine-needle aspiration, open biopsy, and surgical therapy was encountered. No complications occurred. CONCLUSIONS: The use of interventional magnetic resonance imaging to assist with fine-needle aspiration core biopsy has made the biopsy procedure safer and more accurate. Potentially morbid and disfiguring surgeries have been avoided in some patients. Deeper lesions have been more easily approached, as the needle for biopsy is under constant magnetic resonance guidance. Improved visualization for critical structures allows safer performance of biopsies. The primary difficulties of open magnetic resonance imaging relate to the need for nonferromagnetic instrumentation and equipment and their high costs. An inverse relationship exists between the imaging quality and the "dead time" required to acquire images.

Sinusitis complicated by meningitis: current management.

OBJECTIVES: Meningitis is the most common intracranial complication of sinusitis. We review the incidence, current management, outcomes, and complications of this serious infection. Our study also examines the evolving roles of endoscopic sinus surgery and other new therapeutic and diagnostic modalities in our armamentarium. STUDY DESIGN: A retrospective chart review was performed at a tertiary academic medical center of all patients diagnosed with sinusitis with complications between January 1985 and December 1999. METHODS: The patients were divided into two main groups: intracranial versus orbital complications. Meningitis was the most common intracranial complication. Data on patients with sinusitis and meningitis were collected and analyzed. RESULTS: Intracranial complications were present in 39 of 82 patients whereas orbital complications were noted in 43 patients. Twenty-one of the 39 intracranial complications were meningitis. The most common computed tomography finding in adults (54%) was sphenoid sinusitis. All patients with AIDS (6 of 21) had unique cryptococcus meningitis. In patients without AIDS, the most common organism was Streptococcus pneumoniae (10 of 21). The most common sequela was seizure disorder (4 of 21). Endoscopic sinus surgery was performed on 7 of 21 patients. One patient with AIDS who had sinusitis and meningitis died. CONCLUSIONS: Meningitis as a complication of sinusitis may still pose a serious threat. Although outcomes are encouraging, sequelae such as seizure disorders and hearing loss are common complications. The introduction of high-resolution computed tomography scans and magnetic resonance imaging and the availability of wide-spectrum antibiotics have improved our management significantly.

Management of the internal carotid artery during carotid body tumor surgery.

Patients with carotid body tumors require accurate preoperative assessment of vessel involvement and the probable impact of interrupting blood flow through the internal carotid artery. Recent developments in imaging, methods of measuring cerebral blood flow, balloon occlusion testing, and techniques to maintain vascular flow when a graft is required have improved the surgeon's ability to completely resect these tumors with reduced complications. We discuss these methods with respect to our review of 20 carotid body tumors in 18 patients. Twenty-five percent of patients were misdiagnosed, and in four patients injury to the vessel wall required appropriate surgical intervention.

Neurovascular considerations in surgery of glomus tumors with intracranial extensions.

Paragangliomas of the skull base, by virtue of their location, locally infiltrative behavior, and vascular nature, are difficult tumors to resect. Surgical removal is especially complicated when intracranial extensions are encountered. Our experience with a one-stage resection of intracranial extensions of glomus tumors in 20 patients is presented. These 20 patients had a total of 29 paragangliomas: 23 glomus jugulare or tympanicum tumors, 5 carotid body tumors, and 1 pterygopalatine lesion. Ten patients had intradural extension; the other 10 had intracranial extradural tumors. The primary complicating treatment factor was the loss of surgical planes in 6 patients with prior surgery and or radiotherapy. The presence of multiple paragangliomas (20%) and catecholamine secretion by the tumors (15%) complicated surgical treatment as well. Surgical morbidity was primarily related to deficits of lower cranial nerves (50%).

Odontogenic keratocysts: a study of 50 patients.

The odontogenic keratocyst (OKC) is a locally aggressive neoplasm with rates of recurrence reported as high as 60%. Correlation between histopathology and the likelihood of recurrence remains a subject of controversy. In this review of the authors' experience in treating 50 patients with OKC between 1977 and 1993, 58 specimens were studied to correlate the likelihood of recurrence with the presence of the following histologic features--parakeratosis, orthokeratosis, satellite cysts, epithelial rests, or epithelial proliferation. Orthokeratinized cysts were associated with a higher recurrence rate than in previously reported studies. Disruption of the epithelial lining in the resected specimen was found to be a primary determinant of recurrence.

Evaluation of the utility and cost-effectiveness of obtaining histopathologic diagnosis on all routine tonsillectomy specimens.

OBJECTIVES: To evaluate the use and necessity of obtaining histopathology on patients undergoing tonsillectomy, and to provide indications and guidelines for requesting histopathology on tonsillectomy patients. STUDY DESIGN: At the University of Mississippi Medical Center, we have been routinely obtaining histopathologic diagnoses on every patient undergoing tonsillectomy or tonsillectomy and adenoidectomy. Specimens are separated into left and right tonsils and adenoids. This study was designed at our tertiary care academic center to evaluate the necessity for obtaining histopathologic diagnosis on each of these patients. METHODS: A retrospective review of histopathologic reports on all patients in both pediatric and adult age groups undergoing tonsillectomy or tonsillectomy and adenoidectomy between January 1994 and December 1999 was performed. RESULTS: A total of 2438 reports were reviewed. There were 2099 in the pediatric age group and 339 were adults. None of the children had an unusual histopathology finding other than lymphoid hyperplasia. Of the 339 adults, 34 had squamous cell carcinoma and 6 had lymphoma; however, these findings were suspected preoperatively by history and clinical manifestations. CONCLUSIONS: The general practice guidelines mandate obtaining histopathologic diagnoses on most of the tissues received. Based on our review, histopathology of tonsillectomy and/or adenoidectomy may not be necessary, especially in children. In this era of cutting excess costs of health care dollars, waving histopathology in these cases may have major implications without compromising delivery of quality care.

Upper-airway surgery for treating obstructive sleep apnea. Measuring and predicting success.

The effectiveness of upper-airway surgery in treating obstructive sleep apnea was examined in 37 patients. All patients received a uvulopalatopharyngoplasty. Some also received tonsillectomies, septoplasties, and turbinectomies. The success of the operations was evaluated along three dimensions: a decrease in the number of apneas per sleep hour, a reduction in maximum nocturnal oxygen desaturation, and a decrease in daytime somnolence. Over 80% of the patients improved on at least one of these factors following surgery. However, postoperative intercorrelations among these three variables were relatively low. Furthermore, preoperative indexes of apnea severity could not be used to predict the degree of postoperative improvement.

Modern presentations of Bezold's abscess.

The use of antibiotics in suppurative otitis media has greatly diminished the incidence of complications. Deep neck abscess arising from acute mastoiditis, a disease thoroughly described by Frederick Bezold early in this century, has become rare. In the last three years we have treated five cases of deep neck abscess of otogenic origin at our hospital. These cases exemplify Bezold's classic description in their site of origin in the mastoid process and route of spread in the neck. However, our contemporary examples differed in clinical setting, latency of onset, and bacterial cause. In four of the cases, delay in diagnosis occurred because of failure to recognize the disorder. Computed tomography has proved valuable in the anatomic diagnosis and surgical planning. Renewed familiarity with the clinical presentations and pathogenesis of this now uncommon condition may prevent delay in diagnosis and initiation of therapy.