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Biomedical subjects

A Valavanis

Publications and source records attributed to A Valavanis.

140 records · Page 8Linked to original sources
PubMed1978

Computed tomography for small acoustic neuromas.

The minimal size of acoustic neuromas detectable by computered tomography (CT) is, according to the available literature, 1.5 to 2 cm. The new otoneurosurgical technic using the transtemporal and translabyrinthine approach necessitates an early diagnosis of neuromas protruding 1 cm or less into the cerebellopontine angle cistern. This seemed impossible with the available CT equipment. Eight proven acoustic neuromas 1 cm or less in diameter, detected with CT, are reported. Diagnostic criteria are elaborated. The study shows that small cerebellopontine angle tumors can be detected by use of CT machines of the newer generation which perform scanning with thin and overlapping slices.

Aged↗
PubMed1978

Computed tomography of acoustic neuromas with emphasis on small tumor detectability.

The results of CT analysis of 41 acoustic neuromas are presented. Large and medium-sized tumors are easily detected: our results are comparable to the reported findings of other authors. The detectability of small acoustic neuromas is considerably improved by the application of newer-generation CT apparatus and the use of specific scanning parameters, including extremely thin overlapping slices, low scan speed, high gantry tilt, short time between contrast agent application and tumor scanning, and computer-assisted magnification of the posterior fossa.

Humans↗
PubMedDate not supplied

Target definition and trajectory optimization for interactive MR-guided biopsies of brain tumors in an open configuration MRI system.

We present an imaging strategy for planning and guiding brain biopsies in an open configuration MR system. Preprocedure imaging was performed in a 1.5-T MR system and was designed to provide, in a clinically efficient manner, high resolution anatomical and functional/physiologic information for precise definition and tissue characterization of the target, aiming at optimization of the biopsy trajectory for planning a safe and accurate procedure. The interventions were performed in a .5-T open bore magnet, and imaging was optimized to provide the imaging quality and temporal resolution necessary for performing the procedure interactively in near real time. Brain biopsies of 21 patients were performed in a 10-month period. Segmentation and surface rendering analysis of the lesions and vascular structures and dynamic MR perfusion and cortical activation studies provided an efficient and comprehensive way to appreciate the relationship of the target to surrounding vital structures, improved tissue characterization and definition of the tumor margins, and demonstrated the location of essential cortex, allowing appropriate placement of the burr hole and choice of optimal trajectory. Interactive protocols provided good visualization of the target and the interventional devices and offered the operator real-time feedback and control of the procedure. No complications were encountered. Advanced methods of image acquisition and processing for accurate planning of interventional brain procedures and interactive imaging with MR guidance render feasible the performance of safe and accurate neurointerventional procedures.

Adult↗
PubMedDate not supplied

Computed tomography of gliomatosis cerebri.

Two cases of gliomatosis cerebri which underwent serial CT-examination with contrast enhancement and histological examination of autopsy material are presented. No one single CT showed all the lesions discovered on neuropathological examination, the lesions in the brainstem, basal ganglia and cerebellum being isodense. The presentation of the lesions on CT was in both cases different. In one case there were several hypodense areas predominantly scattered throughout the white matter of both hemispheres, in the other the main lesion was a "tumor' of the corpus callosum, which lead to the decision for operation. Both cases showed periventricular enhancement expressing the histologically verified periventricular spread of tumor cells. Contrast enhancement appeared in the late stages of the diseases. In the different diagnosis, pseudotumor cerebri, multiple sclerosis, encephalitis and multiple brain metastases are considered. Bearing the possibility of gliomatosis cerebri in mind, CT would help limit the differential diagnosis, especially on the basis of serial CT examinations and in combination with the clinical course.

Adult↗
PubMedDate not supplied

Blood-brain-barrier disruption in acute Wernicke encephalopathy: MR findings.

The clinical and MR features of an alcoholic woman with Wernicke encephalopathy are reported. During the acute stage Gd-diethylenetriamine pentaacetic acid enhanced MR revealed damage of the blood-brain barrier bilaterally and symmetrically adjacent to the third ventricle, cerebral aqueduct, and fourth ventricle. The enhancement disappeared after successful thiamine therapy, as demonstrated in a repeat postcontrast MR 1 week later.

Adult↗
PubMedDate not supplied

Patency of external and internal carotid artery in the presence of an occluded common carotid artery: noninvasive evaluation with combined cerebrovascular Doppler examination and sequential computertomography.

The patency of the external carotid artery (ECA) and internal carotid artery (ICA) in the presence of an occlusion of the common carotid artery (CCA) was evaluated in 7 patients with a symptomatic CCA occlusion by the combined application of cerebrovascular Doppler examination (cv-Doppler) based on continuous-wave equipment and sequential computertomographic scans with intravenous bolus injection of contrast material (sequential CT-scans). Occlusion of the CCA was demonstrated by cv- Doppler and sequential CT-scans and confirmed by routine angiography. A patent ECA was found in all 7 patients by the combined method, but could not be demonstrated by routine angiography in one of these patients. A patent ICA was found in 2 patients by the combined method, while routine angiographic findings concerning the patency of the ICA were equivocal. An occluded ICA was found in 5 patients by the cv-Doppler-sequential CT-scans method, where routine angiographic findings also were equivocal. Operation to restore blood flow in the CCA was performed in 5 patients and successful in 3 patients in whom blood flow from the CCA to the ECA could be achieved in 2 patients, and to the ECA and ICA in one patient, as predicted by the combined cv-Doppler-sequential CT-scans method. Thus, the patency of the ICA in the presence of a CCA occlusion can be reliably evaluated by the combined diagnostic procedure. The method may help to decide for further diagnostic work-up, e.g., specific selective injections and projections in more than two plans during cerebral angiography, and/or successful surgical intervention in a given patient with a CCA occlusion, even if angiographic findings are equivocal.

Adult↗
PubMedDate not supplied

Spinal cord vascular disease: characterization with fast three-dimensional contrast-enhanced MR angiography.

BACKGROUND AND PURPOSE: Noninvasive characterization of spinal vascular lesions is essential for guiding clinical management, and several MR angiographic techniques have been applied in the past with variable results. The purpose of our study was to assess the potential of a dynamic 3D contrast-enhanced MR angiographic sequence to characterize spinal vascular lesions and to identify their arterial feeders and venous drainage. METHODS: A contrast-enhanced gradient-echo 3D pulse sequence providing angiographic information within 24 seconds was applied prospectively in 12 consecutive patients with a presumed spinal vascular lesion. The images were evaluated for visibility of the arterial feeder, and the results were compared with those of conventional angiography performed the next day. RESULTS: The MR angiographic findings proved that the lesions were correctly characterized as spinal arteriovenous malformations (AVMs) (n = 6), spinal dural arteriovenous fistulas (AVFs) (n = 3), a hemangioblastoma (n = 1), a teratoma (n = 1), and a vertebral hemangioma (n = 1). The arterial feeder was visible in all six AVMs and in the hemangioblastoma, corresponding to conventional angiographic findings. In two of three spinal dural AVFs, an enlarged draining medullary vein was seen within the neural foramen, providing correct localization. The third fistula could not be seen owing to reduced image quality from motion artifacts. CONCLUSION: Fast 3D contrast-enhanced MR angiography is a noninvasive technique with high accuracy in the characterization of spinal vascular disease. Visibility of the arterial pedicles corresponds well with that of digital subtraction angiography, facilitating the management of these patients.

Adult↗
PubMedDate not supplied

Preoperative embolization of the head and neck: indications, patient selection, goals, and precautions.

Preoperative embolization was performed in 39 patients with 44 paragangliomas of the head and neck. Because of their complex vascular supply and their relation to vital structures such as the internal carotid artery and the lower cranial nerves, paragangliomas of the temporal bone represent challenging lesions to both the neuroradiologist and the otoneurosurgeon. Detailed classification by high-resolution CT and recognition of the multi- or monocompartmental vascular composition and of dangerous situations by selective angiography are essential prerequisites for safe and effective devascularization of paragangliomas of the temporal bone. Major complications that may occur if embolic material reaches intraaxial vessels through anastomoses between external carotid artery branches and the internal carotid and/or the vertebral artery can be avoided with the use of specific precautionary techniques. Palsies of the facial and lower cranial nerves can also be avoided if reabsorbable material is used for embolization of vessels supplying cranial nerves in asymptomatic patients. In selected cases with significant supply from the internal carotid artery, special interventional techniques, including embolization of the pericarotid tumor portion through the caroticotympanic artery and pre- or peroperative balloon occlusion of the petrous internal carotid artery, allow radical removal of extensive paragangliomas of the temporal bone. Techniques and selection of materials for embolization of carotid body, vagal body, and other paragangliomas of the head and neck mainly depend on the vascular composition of the tumor and on the specific vascular territory in which the tumor is located. In this series, preoperative embolization significantly improved surgical conditions of paragangliomas of any location in the head and neck and proved to represent an essential prerequisite for successful surgery of extensive paragangliomas of the temporal bone.

Adult↗
PubMedDate not supplied

High-resolution CT investigation of nonchromaffin paragangliomas of the temporal bone.

Twenty-six cases of surgically verified nonchromaffin paragangliomas (NCPs) of the temporal bone were investigated by contrast-enhanced, thin-section, multiplanar high-resolution computed tomography (CT). Based on the high-resolution CT findings the tumors were classified according to a recently introduced surgical classification of NCP into four main types (A, B, C1-C3, and D1-D3). With high-resolution CT tumors were correctly classified in all cases, as was shown with intraoperative correlation. On the basis of these findings, high-resolution CT should replace conventional tomography and should be regarded as complementary to selective angiography in the preoperative evaluation of NCP.

Ear Neoplasms↗
PubMedDate not supplied

Postoperative lumbar CT: technique, results, and indications.

Seventy-seven patients with recurrent radicular symptoms after operation for lumbar disk herniation were examined by plain computed tomography (CT) and by intravenously enhanced CT. With the latter technique, scar tissue and recurrent disk herniation can be distinguished: scar tissue shows definite contrast enhancement whereas recurrent disk herniation remains unenhanced. Nerve roots surrounded by scar tissue are often visualized on the postcontrast scan as rounded lucencies. Symmetrical undisplaced nerve roots were identified in 88% of cases of hypertrophic scar formation; this finding excludes recurrent disk herniation. Dural calcifications were found in five patients with hypertrophic scar formation. The authors conclude that CT with contrast enhancement should be the method of choice for evaluating patients with recurrent radicular symptoms after operation for disk herniation.

Cicatrix↗
PubMedDate not supplied

High-resolution CT of the normal and abnormal fallopian canal.

A two-part anatomic and clinical high-resolution computed tomographic (HRCT) study of the fallopian canal was conducted. From the correlation of HRCT images of eight specimen temporal bones with their corresponding anatomic sectional images, it was evident that the full length of the fallopian canal can be accurately visualized. An axial section demonstrates the labyrinthine segment, geniculate ganglion fossa, and proximal part of the tympanic segment, whereas a Stenver projection is used for the tympanic segment, second knee, and mastoid segment. In clinical studies axial sections simultaneously visualized the proximal parts of the fallopian canal in 82% of 28 cases, whereas Stenver projections simultaneously visualized the distal parts in 75% of 16 cases of acute facial nerve palsy. Twenty-one patients with intratemporal facial nerve palsy and six patients with congenital atresia of the external auditory canal were also examined. HRCT was highly accurate in detecting and defining neoplastic, inflammatory, and congenital lesions of the fallopian canal. A lower rate of detection was recorded for traumatic lesions.

Cranial Nerve Neoplasms↗
PubMedDate not supplied

Contrast-enhanced MR of the facial nerve in patients with posttraumatic peripheral facial nerve palsy.

PURPOSE: To estimate the value of noncontrast and contrast-enhanced T1-weighted MR imaging in detecting the underlying mechanisms of injury and regeneration in immediate- or delayed-onset posttraumatic peripheral facial nerve palsy. METHODS: Twenty-four patients with posttraumatic peripheral facial nerve palsy were examined on a 1.5-T MR imaging unit with precontrast and postcontrast T1-weighted spin-echo and gradient-echo sequences. RESULTS: Abnormal enhancement of the distal intrameatal nerve segment was visible in 92% of the patients up to 2 years after their initial trauma. A hematoma within the geniculate ganglion was seen in 33% of the patients with a longitudinal fracture. The greater superficial petrosal nerve (in 32% of patients) and the geniculate ganglion (in 48% of patients) were thick and intensely enhancing. Hematoma within the cochlea/vestibule or enhancement of the cochlea/vestibule and the vestibulocochlear (eighth) nerve was observed in transverse fractures. CONCLUSION: MR images can show long-lasting abnormal nerve enhancement, especially in the distal intrameatal nerve segment, related to the long-lasting breakdown of the blood/peripheral nerve barrier associated with nerve degeneration and regeneration after traumatic stretching of the greater superficial petrosal nerve. Additionally, intraoperatively observed perineural and intraneural scar formation leads to thickening and intense enhancement of the affected nerve segments on MR images. A hematoma in the region of the geniculate ganglion can be seen in some but not all patients. Associated damage of the inner ear structures in patients with transverse fractures is also visible on MR images.

Adolescent↗