Posterior semicircular canal dehiscence: CT prevalence and clinical symptoms.

OBJECTIVE: To estimate the prevalence of and symptoms associated with posterior semicircular canal dehiscence (PSCD) compared to superior semicircular canal dehiscence (SSCD) and nondehiscent semicircular canals (NDSC). STUDY DESIGN: Retrospective review. SETTING: Academic tertiary referral center. PATIENTS: Review of 412 temporal bone CT scans and associated patient records, excluding patients with prior mastoid or skull base surgery. INTERVENTION(S): CT images (0.625 mm thick) were reviewed in the planes of the semicircular canals. Patient demographics and symptoms were tabulated and analyzed. MAIN OUTCOME MEASURE(S): Prevalence of PSCD and SSCD; degree of hearing loss; presence or absence of aural fullness, autophony, tinnitus, pulsatile tinnitus, disequilibrium, vertigo, and Tullio phenomenon. RESULTS: Review of the 412 CT scans revealed 5 cases of PSCD (1.2%) and 20 cases of SSCD (4.9%). All patients with PSCD were male, aged 16 to 73 years. One patient with PSCD reported tinnitus, autophony, disequilibrium, vertigo, and Tullio phenomenon; 2 patients reported only tinnitus and aural fullness, and 1 patient had no symptoms. PSCD was commonly associated with SSCD. There were no significant differences in symptoms between PSCD patients and the other groups. There were, however, statistically significant differences between SSCD patients and NDSC patients in the rates of autophony, tinnitus, and disequilibrium. CONCLUSION: The prevalence of PSCD in patients undergoing temporal bone CT scans is considerably less than SSCD (1.2% versus 4.9%), and the 2 conditions commonly coexist. Given the small numbers in our study, we were not able to demonstrate any distinguishable clinical features for the PSCD patients.

Gadolinium- and 5-aminolevulinic acid-induced protoporphyrin IX levels in human gliomas: an ex vivo quantitative study to correlate protoporphyrin IX levels and blood-brain barrier breakdown.

In recent years, 5-aminolevulinic acid (ALA)-induced protoporphyrin IX (PpIX) fluorescence guidance has been used as a surgical adjunct to improve the extent of resection of gliomas. Exogenous administration of ALA before surgery leads to the accumulation of red fluorescent PpIX in tumor tissue that the surgeon can visualize and thereby discriminate between normal and tumor tissue. Selective accumulation of PpIX has been linked to numerous factors, of which blood-brain barrier breakdown has been suggested to be a key factor. To test the hypothesis that PpIX concentration positively correlates with gadolinium (Gd) concentrations, we performed ex vivo measurements of PpIX and of Gd using inductively coupled plasma mass spectrometry, the latter as a quantitative biomarker of blood-brain barrier breakdown; this was corroborated with immunohistochemistry of microvascular density in surgical biopsies of patients undergoing fluorescence-guided surgery for glioma. We found positive correlations between PpIX concentration and Gd concentration (r = 0.58, p < 0.0001) and between PpIX concentration and microvascular density (r = 0.55, p < 0.0001), suggesting a significant, yet limited, association between blood-brain barrier breakdown and ALA-induced PpIX fluorescence. To our knowledge, this is the first time that Gd measurements by inductively coupled plasma mass spectrometry have been used in human gliomas.

Genetics of glioblastoma: a window into its imaging and histopathologic variability.

Glioblastoma is a highly malignant brain tumor that relentlessly defies therapy. Efforts over the past decade have begun to tease out the biochemical details that lead to its aggressive behavior and poor prognosis. There is hope that this new understanding will lead to improved treatment strategies for patients with glioblastoma, in the form of targeted, molecularly based therapies that are individualized to specific changes in individual tumors. However, these new therapies have the potential to fundamentally alter the biologic behavior of glioblastoma and, as a result, its imaging appearance. Knowledge about common genetic alterations and the resultant cellular and tissue changes (ie, induced angiogenesis and abnormal cell survival, proliferation, and invasion) in glioblastomas is important as a basis for understanding imaging findings before treatment. It is equally critical that radiologists understand which genetic pathway is targeted by each specific therapeutic agent or class of agents in order to accurately interpret changes in the imaging appearances of treated tumors.

Placement of occipital condyle screws for occipitocervical fixation in a pediatric patient with occipitocervical instability after decompression for Chiari malformation.

In cadaveric studies and recently in one adult patient the occipital condyle has been studied as an option to allow bone purchase by fixation devices. In the current case the authors describe the use of occipital condyle screws in a child undergoing occipitocervical fixation. To the best of the authors' knowledge this case is the first reported instance of this technique in a pediatric patient. This girl had a history of posterior fossa decompression for Chiari malformation Type I when she was 22 months of age. When she was 6 years old she presented with neck pain on flexion and extension of her head. Magnetic resonance imaging in flexion and extension revealed occipitocervical instability. She underwent an occiput to C-2 posterior arthrodesis with bilateral screw placement in the occipital condyles, C-2 lamina, and C-1 lateral masses. Postoperatively, she was neurologically intact. Computed tomography demonstrated a stable construct, and her cervical pain had resolved on follow-up.

Optic canal diameter in infantile osteopetrosis.

Infants with osteopetrosis may present early for ophthalmologic examination because of threatened visual impairment, primarily related to optic nerve compression. The authors describe two children with osteopetrosis who had narrow optic canals on orbital computed tomography. These canals were statistically narrower than those of newly developed, age-matched controls. Optic canal diameters, in addition to visual evoked potential data, may be helpful in determining prognosis.

High-field magnetic resonance imaging of brain iron in Alzheimer disease.

OBJECTIVES: Increased iron deposition in the brain may occur in several neurodegenerative diseases, including Alzheimer disease (AD). Iron deposits shorten T2 relaxation times on T2-weighted magnetic resonance (MR) images. Iron-dependent contrast increases with magnetic field strength. We hypothesized that T2 mapping using 3 T MR imaging (MRI) can disclose differences between normal controls and AD subjects. METHODS: High-resolution brain imaging protocols were developed and applied to 24 AD patients and 20 age-matched controls using 3 T MRI. Eight anatomical regions of interest were manually segmented, and T2 histograms were computed. A visual analysis technique, the heat map, was modified and applied to the large image data sets generated by these protocols. RESULTS: A large number (163) of features from these histograms were examined, and 38 of these were significantly different (P < 0.05) between the groups. In the hippocampus, evidence was found for AD-related increases in iron deposition (shortened T2) and in the concentration of free tissue water (lengthened T2). Imaging of a section of postmortem brain before and after chemically extracting the iron established the presence of MRI-detectable iron in the hippocampus, cortex, and white matter in addition to brain regions traditionally viewed as containing high iron concentrations.

Pediatric ophthalmic computed tomographic scanning and associated cancer risk.

PURPOSE: To review pediatric neuroimaging studies of the head and orbit and the radiation-induced cancer risk associated with computed tomography in light of recent attention to pediatric radioimaging by the US Food and Drug Administration, the National Cancer Institute, pediatricians, and radiologists. DESIGN: Perspective. METHODS: Literature review. SETTING: Institutional. PATIENT POPULATION: Pediatric ophthalmic patients requiring neuroimaging studies. INTERVENTION/PROCEDURE: Review of the current literature. MAIN OUTCOME MEASURES: After review of the current literature and discussion of the related issues, recommendations are made for pediatric neuroimaging studies of the head and orbit. RESULTS: Computed tomography (CT) of the head and orbit may be performed in children with the appropriate indications as long as the radiation exposure is minimized. CONCLUSIONS: Information obtained from CT scans of the head and orbit may determine or affect management in the pediatric ophthalmic population. Because of the concern of cancer induced by radiation exposure in children, neuroimaging modalities without radiation exposure, such as magnetic resonance imaging or ultrasound, may be considered. However, when CT is indicated, it is reasonable and acceptable to perform CT of the head and orbit while minimizing the radiation exposure, thereby adhering to the "ALARA" (as low as reasonably achievable) policy recommended by the US Food and Drug Administration. Further studies of the actual radiation dose delivered during pediatric CT of the head and orbit and the true incidence of radiation-induced cancers after scans are warranted.

MR imaging of the globe and optic nerve.

The superb contrast resolution of MR imaging has significantly improved radiologists' ability to evaluate the anterior visual pathways and globe. Optimal imaging of the orbit requires the radiologist to have a working understanding of the clinical questions the ophthalmologist needs answered. In this article, basic orbit anatomy, MR imaging protocols for the orbit, and common clinical scenarios encountered when imaging the orbit are reviewed, with a focus on the optic nerve and globe.

Calcific cerebral arterial embolization in the setting of bacterial endocarditis superimposed on prior rheumatic aortic valvular disease.

Stroke from a calcific cerebral artery embolus demonstrated by noncontrast computed tomography (CT) is rare. Although the ability of CT to demonstrate early acute cerebral emboli is limited, in the uncommon event of a calcific cerebral embolus, CT can easily visualize the embolized material. We present an unusual case of calcific cerebral arterial embolization to the proximal middle cerebral artery and illustrate the usefulness of CT in diagnosing this rare entity in conjunction with important predisposing clinical factors.

The surgical bed after BCNU polymer wafer placement for recurrent glioma: serial assessment on CT and MR imaging.

OBJECTIVE: The objective of our study was to describe the CT and MR imaging appearances of the surgical bed in the brains of patients receiving biodegradable polymers impregnated with N, N'1, 3-Bis-(2-chloroethyl)-N-nitrosourea (BCNU) for recurrent glioma and to determine whether patients receiving placebos could be differentiated from those receiving BCNU based on the pattern and growth kinetics of tumor recurrence. MATERIALS AND METHODS: The CT and MR images of 20 patients who underwent surgery for resection of recurrent high-grade gliomas and placement of intratumoral wafers (11 received BCNU polymer wafers, nine received control wafers) were analyzed for wafer appearance, volume of gas in the tumor bed, and volume of enhancement on serial scans. RESULTS: Wafers appeared as linear hyperdense structures on CT and as linear low-signal-intensity structures on MR imaging and caused no significant enhancement. In the BCNU polymer group, gas volume was 4.0 +/- 3.4 cm(3) (mean +/- SD), whereas gas volume was 1.6 +/- 3.0 cm(3) for the placebo group (Mann-Whitney test, p = 0.03). A trend toward linear rather than exponential recurrent tumor growth was identified for the BCNU polymer group but not for the placebo group. CONCLUSION: BCNU polymer wafers have a specific appearance on CT and MR imaging with which radiologists should be familiar: gas in the surgical bed is an expected transient finding, and tumor regrowth in patients receiving BCNU polymer wafers appeared to occur at a slower rate than in those receiving the placebo.

CT evaluation of bone dehiscence of the superior semicircular canal as a cause of sound- and/or pressure-induced vertigo.

PURPOSE: To describe the computed tomographic (CT) findings at different collimation widths associated with superior semicircular canal (SSC) dehiscence syndrome and to determine the frequency of these findings in a control population. MATERIALS AND METHODS: Temporal bone CT scans with 1.0-mm and/or 0.5-mm collimation were obtained in 50 patients with sound- and/or pressure-induced vestibular symptoms. The control population consisted of 50 patients undergoing CT at 1.0-mm collimation and 57 patients undergoing CT at 0.5-mm collimation for other reasons. RESULTS: SSC dehiscence was documented on CT scans in all 36 patients with the clinical syndrome, with bilateral findings in six patients. Six other patients without specific clinical signs appeared to have dehiscence on 1.0-mm-collimated scans. Intact bone overlaying the SSC was subsequently identified with 0.5-mm-collimated CT in each case. On the 1.0-mm-collimated scans in 50 control patients, an area judged as possible or definite dehiscence was identified in 18 of 100 ears. The bone overlaying the SSC was intact in each of the 114 control ears evaluated with 0.5-mm-collimated CT. CT findings from the patients with vestibular symptoms combined with those in the control population indicated that the positive predictive value of an apparent dehiscence in the diagnosis of SSC dehiscence syndrome improved from 50% with 1.0-mm-collimated CT with transverse and coronal images to 93% with 0.5-mm-collimated CT with reformation in the plane of the SSC. CONCLUSION: The positive predictive value of CT in identification of SSC dehiscence syndrome improves with 0.5-mm-collimated helical CT and reformation in the SSC plane.

Magnetic resonance imaging findings in a case of cytarabine-induced myelopathy.

A 44-year-old white male with an isolated central nervous system relapse of acute lymphoblastic leukemia was treated with intrathecal cytarabine. He developed Staphylococcus epidermidis meningitis, which was treated successfully with intrathecal vancomycin. Four weeks after the initiation of intrathecal cytarabine, the patient developed progressive ascending paralysis to the upper cervical level. Initial magnetic resonance imaging of the brain and spine were normal, and cerebrospinal fluid evaluation showed no evidence of ongoing infection and clearance of lymphoblasts. Three weeks later, magnetic resonance imaging demonstrated marked edema and peripheral enhancement of the spinal cord, consistent with cytarabine toxicity.

MR imaging of the globe and optic nerve.

MR imaging is an important tool for the evaluation of the optic nerve and globe. A working knowledge of the clinical questions an ophthalmologist faces helps radiologists optimize MR imaging protocols and focus their attention on the important clinical issues.