Venous air emboli identified on head and neck CT scans.

OBJECTIVE: Small venous air emboli probably occur frequently. Our purpose was to describe the locations of small venous air emboli detected on CT scans of the head and neck and their clinical presentations. MATERIALS AND METHODS: The head CT scans of 17 patients and neck CT scans of 10 patients with suspected venous air emboli were reviewed and the locations of the gas collections were recorded. The charts of these patients were reviewed to identify possible sources of these gas collections and any symptoms they may have produced. RESULTS: The most likely source of these gas collections was venous air emboli. The neck CT scans demonstrated gas in the inferior internal jugular vein, subclavian vein, and small anterior neck veins. The head CT scans demonstrated gas in the cavernous sinus, the frontal and temporal scalp, the infratemporal fossa, the carotid canal, the straight sinus, the superior ophthalmic vein, the superior sagittal sinus, extracranially in the region of the foramen magnum, and in a canal in the skull base for an emissary vein or the inferior petrosal sinus. Most of the intravenous lines were placed within 6 h of the scans demonstrating gas. The gas collections did not produce symptoms. CONCLUSION: Asymptomatic venous air emboli can be identified in several locations in the head and neck. The time between manipulation of intravenous lines and the scan, the position of the patient, and the anatomy of the patient probably all affect the likelihood of identifying venous air emboli on CT scans.

Gasserian ganglion: appearance on contrast-enhanced MR.

PURPOSE: To characterize the appearance of the gasserian ganglion on contrast-enhanced MR images. METHODS: We retrospectively reviewed the MR images from 57 patients with suspected pituitary disease. These patients had undergone unenhanced and contrast-enhanced MR imaging of the sella, including evaluation of Meckel's cave. None of the patients had clinical signs or symptoms referable to the fifth cranial nerve or ganglion. Correlation was made with a previous study that compared gross anatomy with high-resolution CT scans of cadaveric specimens. RESULTS: A discrete semilunar enhancing structure within the inferolateral aspect of Meckel's cave was identified in 100 of the 114 caves examined; the other 14 caves had a thickened area of enhancement that blended with the dura inferolaterally. A small semilunar structure within the inferolateral aspect of Meckel's cave was also identified on CT scans of the cadaveric specimens. CONCLUSION: The gasserian ganglion enhances on MR images and should not be confused with a pathologic process.

Accuracy of pedicle screw placement in lumbar fusions by plain radiographs and computed tomography.

STUDY DESIGN: Postoperative radiographs and computed tomography scans were used to evaluate 74 pedicle screws in 16 consecutive patients who underwent lumbar spine fusion with pedicle screw fixation. OBJECTIVE: To evaluate pedicle screw placement using plain radiographs versus computed tomographic scans. SUMMARY OF BACKGROUND DATA: Plain radiographs are the primary means of assessing pedicle screw placement. Comparison of plain radiographs and computed tomography has not been done. METHODS: Screws were graded as IN, OUT, or QUESTIONABLE; the direction of misplacement was noted. All evaluations were performed independently by three observers. RESULTS: Fewer screws were clearly within the pedicle on computed tomography when compared with plain radiographs. Computed tomography showed 10 times as many screws violating the medial cortex as did radiographs. Interobserver differences were not statistically significant. Intraobserver differences approached statistical significance when the two tests were compared. No recognized neurologic complications resulted from pedicle screw placement. CONCLUSIONS: Plain radiographs alone may not accurately reveal pedicle screw placement. Plain radiographs and thin section computed tomographic scans should be used to evaluate postoperative neurologic deficits in patients undergoing instrumented lumbar spine fusion with pedicle screws.

Partial development of the corpus callosum.

PURPOSE: To determine whether the MR findings of callosal dysgenesis suggest that the partially formed corpus callosum in humans is the result of arrested growth or delayed continued development. METHODS: The MR scans of 25 patients with callosal dysgenesis were reviewed to determine whether the observed corpus callosum corresponded to the form and position of a portion of a normal corpus callosum, as suggested by a theory of arrested growth. RESULTS: In 10 of the 25 cases, the partially formed corpus callosum corresponded to a portion of a normal corpus callosum. In the remaining 15 cases, the partially formed corpus callosum was located posterior to the expected location of a normal genu and inferior to the expected location of a normal body. CONCLUSIONS: Corpus callosum dysgenesis in humans may be caused by arrested growth in some cases; in other cases it is most likely caused by delayed continued development that attempts to compensate for earlier abnormalities in the evolution of midline structures.

Posterior fossa venous angiomas with drainage through the brain stem.

PURPOSE: To describe 11 cases of posterior fossa venous angiomas with drainage through the brain stem. METHODS: Eleven cases of posterior fossa venous angioma with drainage through the brain stem were evaluated using MR. Correlation with known routes of venous drainage for the cerebellum and brain stem is made. RESULTS: Six of the 11 venous angiomas were found in the cerebellum, four in the brain stem; one involved both the cerebellum and brain stem. The cerebellar venous angiomas drained to subependymal veins about the fourth ventricle and dorsal pons. These then connected with an enlarged transmesencephalic or transpontine vein, to drain anteriorly to the anterior pontine veins. The brain stem angiomas had variable drainage depending on location. Evidence of hemorrhage was seen in five cases. CONCLUSION: Cerebellar and brain stem venous angiomas have several potential routes of drainage, including an enlarged vein traversing the pons, midbrain, or medulla. A knowledge of the normal venous anatomy of this region helps to understand the occurrence of these uncommon routes of venous drainage.

MRI and clinical findings in rhombencephalosynapsis.

Rhombencephalosynapsis is an unusual disorder characterized predominantly by agenesis/hypogenesis of the cerebellar vermis and fusion of the cerebellar hemispheres. Three cases are reported with emphasis on the MRI and clinical findings. Discussion of the relative importance of the cerebellar anomalies and associated supratentorial abnormalities is included.

MR imaging of the pituitary stalk: size, shape, and enhancement pattern.

The size, shape, signal intensity, and enhancement pattern of the normal pituitary stalk were determined retrospectively by review of MR images of 58 patients. The pituitary stalk was measured at the level of the optic chiasm and at its insertion on the pituitary gland. The contour of the stalk was smoothly tapering, measuring 3.25 +/- 0.56 mm in transverse diameter at the optic chiasm and 1.91 +/- 0.40 mm at its pituitary insertion. The signal intensity of the pituitary stalk on unenhanced T1-weighted images was less than that of the neurohypophysis in all cases and less than that of the optic chiasm in 84% of the cases. After the administration of contrast material, enhancement of the pituitary stalk occurred in all cases. A central area of nonenhancement in an otherwise uniformly enhancing stalk was variably present, depending on the size of the infundibular recess. Our study defines the size, contour, and MR signal characteristics of the normal pituitary stalk. These criteria can be used to distinguish the normal from the abnormal stalk.