Mechanical characterization of structurally porous biomaterials built via additive manufacturing: experiments, predictive models, and design maps for load-bearing bone replacement implants.

Porous biomaterials can be additively manufactured with micro-architecture tailored to satisfy the stringent mechano-biological requirements imposed by bone replacement implants. In a previous investigation, we introduced structurally porous biomaterials, featuring strength five times stronger than commercially available porous materials, and confirmed their bone ingrowth capability in an in vivo canine model. While encouraging, the manufactured biomaterials showed geometric mismatches between their internal porous architecture and that of its as-designed counterpart, as well as discrepancies between predicted and tested mechanical properties, issues not fully elucidated. In this work, we propose a systematic approach integrating computed tomography, mechanical testing, and statistical analysis of geometric imperfections to generate statistical based numerical models of high-strength additively manufactured porous biomaterials. The method is used to develop morphology and mechanical maps that illustrate the role played by pore size, porosity, strut thickness, and topology on the relations governing their elastic modulus and compressive yield strength. Overall, there are mismatches between the mechanical properties of ideal-geometry models and as-manufactured porous biomaterials with average errors of 49% and 41% respectively for compressive elastic modulus and yield strength. The proposed methodology gives more accurate predictions for the compressive stiffness and the compressive strength properties with a reduction of the average error to 11% and 7.6%. The implications of the results and the methodology here introduced are discussed in the relevant biomechanical and clinical context, with insight that highlights promises and limitations of additively manufactured porous biomaterials for load-bearing bone replacement implants. STATEMENT OF SIGNIFICANCE: In this work, we perform mechanical characterization of load-bearing porous biomaterials for bone replacement over their entire design space. Results capture the shift in geometry and mechanical properties between as-designed and as-manufactured biomaterials induced by additive manufacturing. Characterization of this shift is crucial to ensure appropriate manufacturing of bone replacement implants that enable biological fixation through bone ingrowth as well as mechanical property harmonization with the native bone tissue. In addition, we propose a method to include manufacturing imperfections in the numerical models that can reduce the discrepancy between predicted and tested properties. The results give insight into the use of structurally porous biomaterials for the design and additive fabrication of load-bearing implants for bone replacement.

Late-onset temporal lobe epilepsy and dilatation of the hippocampal sulcus by an enlarged Virchow-Robin space.

MRI signal changes within the hippocampal sulcus have been attributed to a dilated Virchow-Robin space within that sulcus, but no clinical correlates have previously been described. We present a 64-year-old man who developed right temporal seizures. MRI revealed an unusually enlarged Virchow-Robin space within the hippocampus, suggesting space-occupying effect. Such an abnormality should be considered a possible etiology in patients with late-onset temporal lobe epilepsy.

Three-dimensional computed tomographic angiography of cerebral aneurysms.

We describe our technique and results of dynamic, reconstructed, three-dimensional (3-D) computed tomographic (CT) angiography in our first 18 patients with either complex aneurysms, producing subarachnoid hemorrhage or the compression of neighboring structures, or small asymptomatic aneurysms, and assess the role of this technique in treatment planning. A dynamic, infused CT scan producing 1.5-mm cuts of the area of interest was performed, and the two-dimensional images were reconstructed in three dimensions with the ISG Allegro system (ISG Technologies, Toronto, Ontario, Canada). Results were compared with intra-arterial digital subtraction angiography and magnetic resonance angiography. All aneurysms over 3 mm and half of the aneurysms less than or equal to 3 mm were demonstrated by 3-D CT angiography. The neck of the aneurysm, its relationship to the parent artery and associated branches, and its relationship to surrounding bony structures, such as the anterior clinoid, were also demonstrated. This was especially useful for ophthalmic aneurysms. The 3-D image could be rotated on the screen to mimic the operative approach. The active, filling portion and the thrombosed part of partially thrombosed, giant aneurysms could be seen on the same image, and the active, filling portion could be better appreciated with 3-D CT angiography than with magnetic resonance angiography. A partially treated, acrylic-coated aneurysm that could not be completely assessed otherwise has been demonstrated by this technique. 3-D CT angiography is useful in the evaluation of aneurysms, especially when the local anatomy is obscured or distorted by its mass or by the anterior clinoid.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of the age of subdural hematomas by computerized tomography.

The computerized tomography (CT) scans of 50 patients with surgically proven subdural hematomas were subdivided into three groups on the basis of the attenuation coefficients of the subdural fluid collections: 28% were more dense, 24% isodense, and 48% less dense than the surrounding brain. The 42 patients with the available data were then subdivided into three groups; acute, subacute, and chronic, according to the time interval between trauma or duration of symptoms and date of CT scanning. Subdural hematomas were found to be hyperdense in 100% of acute patients, isodense in 70% of the subacute group, and hypodense in 76% of the chronic group.

Traumatic intracranial aneurysm due to arterial injury at surgery. Case report.

A case is presented of false intracranial aneurysm of traumatic origin which developed following direct surgical attack on a congenital anterior communicating artery aneurysm. The secondary aneurysm was discovered on the 25th postoperative day and was clipped at a subsequent procedure. The possible pathophysiology is discussed with respect to other direct vessel injuries.

Computerized tomography as a possible aid to histological grading of supratentorial gliomas.

Computerized tomography (CT) is known to be very helpful in demostrating the presence and extent of supratentorial gliomas, practically in combination with intravenous injection of contrast material. Certain specific density patterns were found to exist and enabled us to differentiate with confidence the low-grade gliomas from the glioblastomas. Overlapping did occur, however, as was to be expected, since histological proof was sometimes obtained by the needle biopsy with its inherent doubt as to true tumor representation. Future CT techniques such as sequential scanning after intravenous injection of contrast material may further increase the usefulness of CT scans in the diagnosis and therapeutic approach to the patient with a suspected glioma.

Electroencephalography, magnetic resonance imaging and pathology in patients treated surgically for temporal lobe epilepsy.

In a consecutive series of 40 patients selected by EEG studies for surgical treatment of temporal lobe seizures, magnetic resonance imaging showed structural lesions in 25% and signal abnormalities, usually in the mesial temporal region, in another 35%. Pathological changes included structural lesions in over 30% of patients and sclerosis of the amygdala in almost half of the series. These findings further substantiate the implication of the amygdala in the pathogenesis of temporal lobe seizures with automatism and amnesia.

The role of computed tomographic angiography in the assessment of intracranial vascular disease.

Both technical and clinical implications of three-dimensional computed tomographic angiography in the evaluation of intracranial circulation, and in particular cerebral aneurysms, are presented. Three-dimensional computed tomographic angiography allows excellent visualization of the aneurysm, its neck, and its relationship with the parent artery and important adjacent bony structures. This technique has a major role in the evaluation of difficult aneurysms. In addition, advantages and disadvantages are discussed in comparison with more conventional techniques such as magnetic resonance imaging, magnetic resonance angiography, and digital subtraction angiography. Three-dimensional computed tomographic angiography will continue to develop with the advent of more rapid computed tomography scanners, playing a key role in the investigation and screening of patients with a family history of cerebral aneurysms.

[Angiolipoma of the central nervous system]. / Angiolipomes du système nerveux central.

Angiolipomas of the central nervous system are rare tumors (37 cases in the literature) and are mostly located in the spine (95%), rarely in the skull. When they are intraspinal, these masses are extradural in more than 90% of the cases. Angiolipomas are benign tumors containing vascular and mature adipose elements. The clinical symptomatology is non specific, but computed tomography and mostly MRI provide a precise diagnosis. With 2 additional cases and a review of the literature, we define the main characteristics of these tumors.

[Sub-callus epidermoid cyst. A case report]. / Kyste épidermoïde sus-calleux. A propos d'un cas.

The cranio-encephalic epidermoid cysts are rare tumors. These lesions are extra-axial and can occur at the infratentorial or supratentorial level. The epidermoid cysts are classically in contact with the base of the skull, and less often intraventricular; the other locations are exceptional. Because of their CT aspect (hypodense lesion, rarely isodense, well defined, without contrast enhancement, and without surrounding edema) and MR aspect (in more than 70% of the cases: more or less homogeneous lesion, hypointense in T1 and hyperintense in T2), the authors believe that it is possible to suggest such a diagnosis even with an atypically located case. We report the case of an epidermoid cyst located between the corpus callosum and the falx cerebri.

[A simplified terminology for abnormalities of the lumbar disks]. / Une terminologie simplifiée des anomalies des disques lombaires.

The terminology for abnormalities of the lumbar disk has always been a source of confusion. Recent advances in pathological studies have inspired the authors to propose a simple classification of common disk anomalies suitable not only for diagnostic radiologists but also for referring clinicians. Although the diagnosis of a few pathological entities will only be possible with specific imaging techniques, the proposed classification is appropriate for reporting observations from plain films, conventional tomograms, myelograms, discograms, computed tomography scans and magnetic resonance images. All lumbar disks can thus be classified into one or more of the following categories: normal, aging, scarred, ruptured and herniated. A disk herniation is defined as a localized exit of disk material beyond the limits of the original intervertebral space.

MR imaging features of amyloid-related imaging abnormalities.

BACKGROUND AND PURPOSE: AD is one of the few leading causes of death without a disease-modifying drug; however, hopeful agents are in various phases of development. MR imaging abnormalities, collectively referred to as amyloid-related imaging abnormalities, have been reported for several agents that target cerebral Aß burden. ARIA includes ARIA-E, parenchymal or sulcal hyperintensities on FLAIR indicative of parenchymal edema or sulcal effusions, and ARIA-H, hypointense regions on gradient recalled-echo/T2* indicative of hemosiderin deposition. This report describes imaging characteristics of ARIA-E and ARIA-H identified during studies of bapineuzumab, a humanized monoclonal antibody against Aß. MATERIALS AND METHODS: Two neuroradiologists with knowledge of imaging changes reflective of ARIA reviewed MR imaging scans from 210 bapineuzumab-treated patients derived from 3 phase 2 studies. Each central reader interpreted the studies independently, and discrepancies were resolved by consensus. The inter-reader κ was 0.76, with 94% agreement between neuroradiologists regarding the presence or absence of ARIA-E in individual patients. RESULTS: Thirty-six patients were identified with incident ARIA-E (17.1%, 36/210) and 26 with incident ARIA-H (12.4%, 26/210); of those with incident ARIA-H, 24 had incident microhemorrhages and 2 had incident large superficial hemosiderin deposits. CONCLUSIONS: In 49% of cases of ARIA-E, there was the associated appearance of ARIA-H. In treated patients without ARIA-E, the risk for incident blood products was 4%. This association between ARIA-E and ARIA-H may suggest a common pathophysiologic mechanism. Familiarity with ARIA should permit radiologists and clinicians to recognize and communicate ARIA findings more reliably for optimal patient management.

Imaging in primary central nervous system lymphoma.

Primary central nervous system (CNS) lymphoma (PCNSL) accounts for approximately 3% of all primary CNS tumors. Congenital or acquired immunodeficiency is the only established risk factor for PCNSL. Rates decreased slightly in the mid-1990s, concordantly with the decreasing rates of AIDS. However, the incidence has been increasing in the elderly immunocompetent population, and this trend seems to be independent of improvements in diagnostic techniques, and of overall trends in the incidence of brain tumors and systemic lymphomas. This study presents our experience with the imaging features of PCNSL. Computed tomography (CT) and magnetic resonance imaging (MRI) findings were reviewed in a series of 38 cases of pathologically proven PCNSL. The incidence rate of PCNSL was higher in men than in women (58% versus 42%). Mean age at presentation was 63 years; 120 lesions were demonstrated in the 38 patients, with a 53% frequency of tumor multiplicity. Both CT and MR mainly showed solitary or multiple well-defined round or oval-shaped mass lesions, typically hyperdense on unenhanced CT scans, iso to hypointense on T2 MR weighted images. These lesions also showed an increased signal intensity on diffusion-weighted images. Virtually all lesions enhanced after intravenous administration of contrastmedium. On (1)H-magnetic resonance spectroscopy ((1)H-MRS) most lesions presented increased Cho/Cr, Cho/NAA and lactate/Cr ratios when compared to normal gray matter. No changes in the imaging presentation have occurred over the past two decades, apart from lesions now being smaller at diagnosis. Our imaging findings are in agreement with the existing literature data and with the reported increasing trend of multifocal tumors. Our epidemiologic results add value to the existing evidence of increasing incidence rates among the immunocompetent elderly population.

Myoinositol trends in different types of brain lesions.

Myoinositol (Myo) is a not yet well known metabolite detected using short echo time proton magnetic resonance spectroscopy (HMRS). We examined the role of Myo in 26 patients with new diagnosis of brain lesions including tumors, inflammatory and infectious processes. Histological confirmation of the diagnosis was obtained during gross total surgical resection or stereotactic biopsy of the lesions. The highest ratios of Myo/Cr were found in the hemangiopericytoma and meningioma followed by cortical dysplasia, low grade gliomas, gliobastomas, lymphomas, demyelinating lesions and toxoplasmosis. There was no Myo detected in the cases of metastasis and abscess. Increased Myo levels correlated with low grade gliomas suggesting its potential use in the differentiation of glial tumor. Myo demonstrated a unique pattern in hemangiopericytoma.

Is bone enhancement a helpful finding in the diagnosis of convexity meningiomas?

We have assessed the enhancement of the overlying bone as a new finding in patients with convexity meningioma. This finding was present in 68.6% of cases in our series. This finding was found very helpful in the differential diagnosis of atypical and cystic meningiomas.

Production and properties of bacteriocin-like inhibitory substances from the swine pathogen Streptococcus suis serotype 2.

Streptococcus suis serotype 2 is a major pathogen found in the upper respiratory tract of swine. In this study, isolates of this bacterial species were tested for the production of bacteriocin-like inhibitory substances (BLIS). Of the 38 strains tested, four inhibited the growth of other S. suis isolates according to a deferred-antagonism plate assay. Interestingly, three of the strains were originally isolated from healthy carrier pigs and were considered nonvirulent. Three isolates (94-623, 90-1330, and AAH4) that produced BLIS in liquid broth were selected for further characterization. None of the inhibitory activities was related to the production of either organic acids or hydrogen peroxide. The BLIS produced by these strains were heat stable and proteinase K, pronase, and elastase sensitive but were trypsin and chymotrypsin resistant. They were stable at pH 2 and 12 and had molecular masses in the range of 14 to 30 kDa. Maximum production was observed during the mid-log phase. Following a curing procedure with novobiocin, only 90-1330 lost the ability to produce BLIS, suggesting that the BLIS might be plasmid encoded. Analysis of the inhibitory spectra revealed that the BLIS-producing strains also inhibited the growth of Actinobacillus minor, Actinobacillus porcinus, Enterococcus durans, Micrococcus luteus, Streptococcus agalactiae, Streptococcus dysgalactiae subsp. dysgalactiae, Streptococcus equi subsp. zooepidemicus, and S. dysgalactiae subsp. equisimilis. This study reports for the first time the ability of the swine pathogen S. suis serotype 2 to produce BLIS with the characteristics of classic bacteriocins. Further studies are required to investigate the possibility of using bacteriocin-producing strains to prevent swine infections caused by virulent strains of S. suis serotype 2.

Hypoglossal paralysis due to compression by a tortuous internal carotid artery in the neck.

Severe hemiatrophy of the right half of the tongue in a 22 year old patient was demonstrated to be due to compression of the hypoglossal nerve by a tortuous internal carotid artery in the neck. The nerve was trapped between an abnormal loop of the internal carotid artery and the sternocleidomastoid branch of the occipital artery. Although impairment of cranial nerve function with cases of tortuous and dilated vessels has been reported frequently, twelfth nerve palsy has never been demonstrated before.