On Natural History and Management of Colloid Cysts: Time to Rethink?

BACKGROUND

Colloid cysts, although benign, may occasionally cause obstructive hydrocephalus and sudden death. Reliable prognostic factors for symptomatic progression have been sought, with heterogenous results.

METHODS

We conducted a retrospective review of all cases of colloid cysts of the third ventricle managed at our center between 2009 and 2019. Clinical and neuroimaging characteristics were analyzed using logistic regression in relation to symptomatic status and hydrocephalus. The cutoff values for outcome prediction were calculated using the receiver operating characteristic curve analysis.

RESULTS

There were 82 patients with colloid cysts, of whom 60 were asymptomatic and 22 symptomatic. None of the asymptomatic patients experienced acute neurologic decline or hydrocephalus during follow-up, whereas half (n = 11) of the symptomatic patients presented with hydrocephalus, 8 of whom had acute hydrocephalus. We found 3 putative candidate risk factors for symptomatic colloid cysts: T1-weighted magnetic resonance imaging hyperintense/mixed signal appearance (P = 0.004), location in risk zone I (P = 0.007), and a volume >236.49 mm³ (P = 0.007). Cyst diameter and volume/foramen of Monro diameter ratios had a decreasing trend over time among asymptomatic patients, providing new insights into the natural history of the disease.

CONCLUSIONS

Only a few asymptomatic colloid cysts showed progression requiring surgery, with no acute deterioration or fatal events, whereas the rest remained stable over time, thus supporting a more conservative approach for this group of patients. Higher risk for developing symptomatic colloid cyst was defined by a risk score that included T1-weighted magnetic resonance imaging appearance, risk zone, and colloid cyst volume, aiding the detection of patients at risk of clinical deterioration.

Energy cost determination using a portable accelerometer

The purpose of this study was to determine the physical activity of physical therapists during clinical practice. Nineteen physical therapists from three clinical facilities wore portable accelerometers on their waist belts or chest pockets for the duration of their work shifts. The subjects repeated the experiment on the second day. The accelerometer readings (in arbitrary units) were converted to oxygen consumption VO2 and energy expenditure (kcal) values using previously derived regression equations. The PTs worked an average of 7.9 hours during each shift. The total energy expended during the work shift ranged from 933.6 to 1,689.6 kcal. A correlation coefficient of .91 was found between the accelerometer readings (count X hr-1) recorded on day 1 and day 2 of the study. The analysis of variance revealed that the PTs in the three clinical facilities were not significantly different in age, height, and work-shift duration, but were significantly different (p less than .05) in weight, mean accelerometer readings, and estimated VO2 (L X min-1). When the VO2 was expressed in mL X kg-1 X min-1, no significant difference was found between the PTs in the three clinical facilities. The implications and limitations of the findings are discussed.

Screen/film system speed: its dependence on x-ray energy

Dependence of the speed of various screen/film systems on x-ray energy was studied using the nearly monoenergetic x rays emitted by a filtered fluorescent source. The results show that response depends on screen phosphor composition and thickness. Barium and rare earth screens having K absorption energies lower than that of calcium tungstate are relatively more sensitive to x rays in the 40-70-keV region.

Validity of computer simulation of blood vessel imaging in angiography

The computer-simulation technique for imaging of vessels in angiography is being recognized as a useful tool for the study of the effect of physical parameters on the vessel image. We have examined the validity of this technique by comparing the computed image distribution directly with experimental results. The imput x-ray pattern of a blood vessel phantom, the LSF of the focal spot, and the LSF of a screen-film system were measured. From the data obtained, the final image distributions of the phantom were computed and compared with the experimentally determined distributions. A high-precision device for the alignment and positioning of the vessel phantom was employed in the experiments. Results indicate that computer simulation can correctly predict the image distribution of the blood vessel phantom.

Application of longitudinal magnification effect to magnification stereoscopic angiography: a new method of cerebral angiography

A new method of stereoscopic cerebral angiography has been developed which employs 2X radiographic magnification. In order to obtain the same depth perception in the object as with conventional contact stereoscopic angiography, one can made the x-ray exposures at two focal spot positions which are separated by only 1 inch (2.5 cm), whereas the contact technique requires a separation of 4 inches (10 cm). The smaller distance is possible because, with 2X magnification, the transverse detail in the object is magnified by a factor of two, but the longitudinal detail, which is related to the stereo effect, is magnified by a factor of four, due to the longitudinal magnification effect. The small focal spot separation results in advantages such as improved stereoscopic image detail, better image quality, and low radiation exposure to the patient.

Comparison of convolution and ray-tracing methods for computing small blood vessel images in angiography

Two methods for computing x-ray images of small blood vessels in angiography are presently available, namely, convolution and ray tracing. The convolution method, which is simpler and more powerful than the ray-tracing method, is based on the assumption that blood vessel imaging is isoplantic, whereas ray tracing is considered to provide correct images. In this study, the approximation error (difference between two images, normalized by the maximum value) due to nonisoplanatic imaging was determined by computation of blood vessel images according to both methods. The approximation error for geometric conditions normally encountered in angiography was less than 0.01. It is concluded that an approximation error of this magnitude is negligible and that the convolution method can be applied instead of the ray-tracing method for the computation of images of small blood vessels.

The effect of x-ray spectra from molybdenum and tungsten target tubes on image quality in mammography

The measured x-ray spectra from a molybdenum anode Senographe mammography unit and a tungsten anode unit were used to calculate the x-ray energy spectra transmitted through various thicknesses of fat and water (breast-equivalent materials). The dependence of subject contrast and patient exposure on (a) x-ray spectra, (b) attenuation properties of two breast-equivalent materials, and (c) thickness of breast-equivalent material was predicted. Radiographs of resected breast tissue confirmed these predictions and demonstrated the general relative effects of x-ray beam quality on image contrast in mammography.

Comparison of image quality obtained with optical and radiographic magnification techniques in fine-detail skeletal radiography: effect of object thickness

High-resolution radiography may be done using either optical or radiographic magnification. In the former technique, industrial Type M film was used without screens and the image was viewed with 4-10X optical magnification. In the latter technique, RP film was used with Detail screens and 4X geometric magnification together with a microfocus x-ray tube having a nominal focal spot size of 50 mum. The imaging properties of both techniques were evaluated by means of H & D curves, modulation transfer functions, and Wiener spectra. It was found that for thin objects such as the hand, optical magnification provides better bone images than radiographic magnification; whereas for thicker parts such as the knee, radiographic magnification is superior.

X-ray images of small blood vessels in angiography: question of isoplanatism

The basic theory of x-ray image formation of blood vessels, which is related to isoplanatism, is discussed. The x-ray intensity distributions of the blood vessel images are derived first for the actual case, which gives "correct" x-ray images obtained by the ray-tracing method. Secondly, as an approximation of the actual case, the image distributions are derived by the convolution method, which corresponds to an isoplanatic case. It is concluded that, under practical conditions, x-ray images of blood vessels are given approximately by a convolution integral of the object distribution, that is, the input x-ray pattern of the vessel exposed with a parallel x-ray beam, with the line spread function of geometric unsharpness. Therefore, this theory provides support for the experimental procedure commonly used in obtaining blood vessel images, and for the validity of applying in angiography the concept of the line spread function and the modulation transfer function of geometric unsharpness.

New device for accurate measurement of the x-ray intensity distribution of x-ray tube focal spots

A new device has been developed with which the focal spot distribution can be measured accurately. The alignment and localization of the focal spot relative to the device are accomplished by adjustment of three micrometer screws in three orthogonal directions and by comparison of red reference light spots with green fluorescent pinhole images at five locations. The standard deviations for evaluating the reproducibility of the adjustments in the horizontal and vertical directions were 0.2 and 0.5 mm, respectively. Measurements were made of the pinhole images as well as of the line-spread functions (LSFs) and modulation transfer functions (MTFs) for an x-ray tube with focal spots of 1-mm and 50-mum nominal size. The standard deviations for the LSF and MTF of the 1-mm focal spot were 0.017 and 0.010, respectively.

Effect of focal spot distribution on blood vessel imaging in magnification radiography

From a computer simulation study of blood vessel imaging with uniform, triangular, gaussian, and twin gaussian line spread functions (LSF) corresponding to various focal spot distributions, it is found that vessel images magnified less than 6 times are not strongly dependent upon the focal spot distributions when the size of the focal spot is equal to or smaller than the vessel diameter. When the focal spot is larger than the vessel, image distributions vary appreciably with focal spot distributions, except at low magnification. It is concluded that, in many practical cases, the focal spot distribution does not seriously affect magnified image distributions of blood vessels.

Longitudinal magnification in radiologic images of thick objects: a new concept in magnification radiography

New concepts which are useful for evaluating image resolution and distortion in magnification radiography are introduced. It is shown theoretically and experimentally that "longitudinal magnification" defined as the ratio of the magnified image size to the conventional image size for objects located in a plane perpendicular to the film, is given approximately by the square of the conventional magnification. Resolution in the radiographically magnified image of such objects is much higher than that obtained by optical magnification. This is confirmed experimentally by radiographs of square-wave test objects. The related image distortion is also discussed.

Effect of film graininess and geometric unsharpness on image quality in fine-detail skeletal radiography

Three direct x-ray films and three geometric conditions were used to study the effect of noise and sharpness on high resolution radiography of the hand. The Wiener spectrum of film graininess and the MTF of geometric unsharpness were measured. Radiographs of a wire mesh and a hand phantom, together with the Wiener spectra and MTFs, led to the following conclusions regarding fine-detail skeletal radiography, as currently employed: 1) bone structure detectable in vivo does not show minute structural detail; 2) the technique is primarily noise-limited; 3) the use of better geometry or finer grain film for improving resolution or noise is of limited practical value, whereas the use of poorer geometry or more noisy film results in appreciable degradation of skeletal images; and 4) the present standard technique for in vivo radiography of the hand, therefore, may be very nearly optimal for clinical applications.

The effect of geometric and recording system unsharpness in mammography

Modulation transfer functions (MTFs) and test object radiographs were used to study the effect of geometric and recording system unsharpness in mammography with the CGR Senographe x-ray unit. Results show that geometric unsharpness can be a significant factor in the detection of microcalcifications within the breast, depending on the size and shape of the focal spot, the focal spot-to-recording system distance, and the object-to-recording system distance (o.r.d.). A new recording system for mammography, the DuPont Lo-dose system, requires approximately 1/15th the exposure of a direct x-ray film, such as Kodak RP/M, to provide mammograms with comparable photographic density. With the Lo-dose system, geometric unsharpness can be reduced by use of a specially designed long cone with an increased focal spot-to-recording system distance. This cannot be accomplished with direct x-ray films because the x-ray unit is operating at near-maximum output conditions even when short cones are used. Although direct x-ray films have a higher resolution than the Lo-dose system, at certain o.r.d.s total resolution is found to be affected more significantly by geometric unsharpness than by the Lo-dose recording system. In several cases, clinical results show improved detection of microcalcifications at larger o.r.d.s by the Lo-dose system with a long one, combined with a reduction by a factor of 15 in patient exposure.