Browsing by Author "Malinzak, Michael D"

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    Intraspecific variation in semicircular canal morphology-A missing element in adaptive scenarios?
    (American journal of physical anthropology, 2019-01) Gonzales, Lauren A; Malinzak, Michael D; Kay, Richard F
    OBJECTIVES:Recent evidence suggests that the amount of intraspecific variation in semicircular canal morphology may, itself, be evidence for varying levels of selection related to locomotor demands. To determine the extent of this phenomenon across taxa, we expand upon previous work by examining intraspecific variation in canal radii and canal orthogonality in a broad sample of strepsirrhine and platyrrhine primates. Patterns of interspecific variation are re-examined in light of intraspecific variation to better understand the resolution at which locomotion can be reconstructed from single individuals. MATERIALS AND METHODS:Data was collected from high-resolution CT scans of 14 size-matched, related species. Six of these taxa have existing data on rotational head speeds. RESULTS:The level of intraspecific variation was found to differ in strepsirrhine and in platyrrhine species pairs, with larger ranges of variation generally observed for the slower moving taxon than the faster moving one. Taxa that are classified as relatively agile can to some extent be separated from those who are slower-moving, but only when comparing similarly sized, closely related species with more extreme forms of locomotion. DISCUSSION:Our findings agree with previous research showing that canal intraspecific variation can fluctuate according to species-specific locomotor behavior and extends this further by identifying behaviors that may be under unusual selective pressure. It also demonstrates the complexity of interpreting inner ear morphology in the context of broadly applicable locomotor "categories" of the kind commonly used in behavioral studies. We suspect that simplified models predicting vestibular sensitivity may be unable to differentiate behaviors when only a single specimen is available.
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    Locomotor head movements and semicircular canal morphology in primates.
    (Proc Natl Acad Sci U S A, 2012-10-30) Malinzak, Michael D; Kay, Richard F; Hullar, Timothy E
    Animal locomotion causes head rotations, which are detected by the semicircular canals of the inner ear. Morphologic features of the canals influence rotational sensitivity, and so it is hypothesized that locomotion and canal morphology are functionally related. Most prior research has compared subjective assessments of animal "agility" with a single determinant of rotational sensitivity: the mean canal radius of curvature (R). In fact, the paired variables of R and body mass are correlated with agility and have been used to infer locomotion in extinct species. To refine models of canal functional morphology and to improve locomotor inferences for extinct species, we compare 3D vector measurements of head rotation during locomotion with 3D vector measures of canal sensitivity. Contrary to the predictions of conventional models that are based upon R, we find that axes of rapid head rotation are not aligned with axes of either high or low sensitivity. Instead, animals with fast head rotations have similar sensitivities in all directions, which they achieve by orienting the three canals of each ear orthogonally (i.e., along planes at 90° angles to one another). The extent to which the canal configuration approaches orthogonality is correlated with rotational head speed independent of body mass and phylogeny, whereas R is not.
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    Myelography Using Energy-Integrating Detector CT Versus Photon-Counting Detector CT for Detection of CSF-Venous Fistulas in Patients With Spontaneous Intracranial Hypotension.
    (AJR. American journal of roentgenology, 2024-01) Schwartz, Fides R; Kranz, Peter G; Malinzak, Michael D; Cox, David N; Ria, Francesco; McCabe, Cindy; Harrawood, Brian; Leithe, Linda G; Samei, Ehsan; Amrhein, Timothy J
    Background: CSF-venous fistulas (CVFs) are an increasingly recognized cause of spontaneous intracranial hypotension (SIH) that are often diminutive in size and exceedingly difficult to detect by conventional imaging. Objective: This study's objective was to compare EID-CT myelography and PCD-CT myelography in terms of image quality and diagnostic performance for detecting CVFs in patients with SIH. Methods: This retrospective study included 38 patients (15 men, 23 women; mean age, 55±10 years) with SIH who underwent both clinically indicated EID-CT myelography (slice thickness, 0.625 mm) and PCD-CT myelography (slice thickness, 0.2 mm; performed in ultrahigh-resolution mode) to assess for CSF leak. Three blinded radiologists reviewed examinations in random order, assessing image noise, discernibility of spinal nerve root sleeves, and overall image quality using 0-100 scales (100=highest quality), and recording locations of CVFs. Definite CVFs were defined as CVFs described in CT myelography reports using unequivocal language and showing attenuation >70 HU. Results: For all readers, PCD-CT myelography, in comparison with EID-CT myelography, showed higher image noise (reader 1: 69±19 vs 38±15; reader 2: 59±9 vs 49±13; reader 3: 57±13 vs 43±15), higher nerve root sleeve discernibility (reader 1: 84±19 vs 30±14; reader 2: 84±19 vs 70±19; reader 3: 60±13 vs 52±12), and higher overall image quality (reader 1: 84±21 vs 40±15; reader 2: 81±10 vs 72±20; reader 3: 58±11 vs 53±11) (all p<.05). Eleven patients had a definite CVF. Sensitivity and specificity for detection of definite CVF for EID-CT myelography and PCD-CT myelography for reader 1 were 45% and 96% versus 64% and 85; for reader 2 were 36% and 100% versus 55% and 96%; and for reader 3 were 45% and 100% versus 55% and 93%. For all readers, PCD-CT myelography, in comparison with EID-CT myelography, showed significantly higher sensitivity (all p<.05), without significant difference in specificity (all p>.05). Conclusion: In comparison with EID-CT myelography, PCD-CT myelography yielded significantly improved image quality with significantly higher sensitivity for CVFs without significant loss of specificity. Clinical Impact: The findings support a potential role of PCD-CT myelography in facilitating earlier diagnosis and targeted treatment of SIH, avoiding high morbidity during potentially prolonged diagnostic workups.