Biomedical subjects
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Two cases of cystic metastatic melanoma are presented. The only reliable computed tomography sign of a true cystic lesion is the presence of an interface, such as between blood and tumor fluid. Differentiation of cystic metastatic melanoma from other cystic lesions of the brain is discussed.
The CT findings in 16 patients with histologically proved primary central nervous system (CNS) reticulum cell sarcoma (RCS) showed this malignancy to have predilection for the basal ganglia and thalamus, the periventricular white matter, the corpus callosum, and the vermis cerebelli. In 43% of patients with untreated tumor it presented as multifocal lesions; in each of these patients the basal ganglia were involved in conjuction with another site. In the other 57% of patients with untreated tumor presenting as solitary lesions the basal ganglia, the corpus callosum, and the frontal lobe were sites of predilection. Such solitary lesions may be indistinguishable from other tumors. Contrast enhancement of RCS was characteristically homogeneous with rare lucency, even in very large lesions.
Simultaneous 111In-DPTA and metrizamide CT cisternography correlated closely in the qualitative imaging of cerebrospinal fluid (CSF) dynamics in 9 normal patients and in 11 patients thought to have communicating hydrocephalus. CSF clearance of both tracers was similar; significant absorption occurred in the spinal dural sac. Although delayed elevated serum iodine levels correlated highly with abnormal persistent ventricular penetration (detection at 48 hours), these levels cannot be used to predict abnormal ventricular stasis. The pattern of ventricular and cortical sulcus enlargement on the plain CT scan did not indicate whether the dynamic metrizamide cisternogram would be normal or abnormal.
Application of computed tomography (CT) to neck masses has received little attention. The authors reviewed 10 cervical masses studied with CT as well as conventional imaging modalities. CT was extremely useful in defining both the osseous and soft-tissue extent of the lesion. In several instances, CT was able to show the relationship of the tumor to the spinal canal. When combined with angiography, CT demonstrated the relationship of the major cervical vascular channels to the lesion. Pathological conditions included neurofibroma, chordoma, branchial cleft cyst, neuroblastoma, lymphoma, neurilemmoma, and metastatic carcinoma.
Computerized tomography as a diagnostic procedure is characterized by its high sensitivity but limited specificity. This lack of specificity may result in an erroneous diagnosis and, possibly, in ill-advised therapy unless clinical and objective data are carefully considered in interpreting the study. The most common pitfalls encountered are the phenomena of contrast enhancement of infarcts and mass effect associated with infarcts. Many different pathological processes can have similar enhancement patterns. The evolution of high density, acute hemorrhage to isodense areas in the chronic hematoma can become a serious diagnostic problem unless an appropriate history is available. The authors discuss 30 cases in which misinterpretation of CT scans resulted in erroneous diagnoses. Seventeen of these patients underwent operation.
Meningiomas have been reported to have associated areas of surrounding low density on computerized tomography (CT). These low-density areas may represent edema, widened subarachnoid spaces, loculated cerebrospinal fluid, demyelination, or adjacent tumor. Two cases are presented in which this adjacent area of low density represented a tumor cyst. Recognition is important as the CT appearance of these lesions may simulate a metastatic tumor.
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A clinical study comparing the relative sensitivities of computed tomography, skull radiography, and radionuclide scanning in the detection of skull metastases indicated that CT was the least sensitive of these three modalities. CT could however detect a majority of lesions if scans were viewed at appropriate window settings. Phantom studies showed that the limitations of CT can be related to limited spatial resolution, the density of the lesions, partial volume averaging, and plane of section.
Phantom studies comparing skull radiography and cranial computed tomography (CT) show that CT is 5 to 15 times more sensitive than skull radiography in the detection of intracranial calcifications. The difference in detectability varies with object size. The relative sensitivity of CT increases with increased object size within the constraints of the section thickness. The relationship of these findings to the detectability of pineal and choroid calcifications is discussed.
Various contrast agents with either sodium or meglumine cations and iothalamate and diatrizoate anions are compared in a series of patients with malignant gliomas. There is no difference in the ability of these agents to enhance tumors in cranial computed tomography.
The CT appearance of metastatic malignant melanoma is varied, but it can show features suggesting the correct diagnosis. Intracerebral hemorrhage alone, associated with an adjacent tumor nodule or mixed diffusely with a tumor, occurred in 10 of 33 patients. Identification of a tumor nodule is important, since it may be the site of recurrent hemorrhage if not removed completely at surgery. Unusual presentations such as meningeal carcinomatosis and lesions simulating primary gliomas also occurred.
The course of 36 patients with medulloblastoma and ependymoma was evaluated prospectively by clinical examination, radionuclide (RN) studies and computed tomography (CT). Seventeen of the 36 patients (47%) had tumor recurrence. Twelve (41%) of the 29 patients with medulloblastoma had recurrent tumors of which 7 of 12 (58%) were at the primary site and 2 of 12 (17%) were within the ventricles while 10 of 12 (83%) were in the subarachnoid space. Five of the 7 patients with ependymoma had recurrent tumors. In 4 of the 5 patients tumor recurred at the primary site while subarachnoid seeding occurred in 2 of 5 patients (40%) and intraventricular metastases were found in 4 of 5 patients (80%). Progressive ventricular enlargement often accompanied subarachnoid seeding, presumably secondary to obstruction of cerebrospinal fluid (CSF) flow in the subarachnoid pathways. CT and RN scans were frequently complementary in detecting tumor recurrence.
On the initial computed tomographic (CT) scan in 10 of 13 patients with herpes simplex encephalitis (HSE), the most characteristic finding was a unilateral, low-density lesion in the medial temporal lobe and/or insular cortex. This lesion was seen in all patients as the disease progressed. When associated with hemorrhage and streaked contrast enhancement this lesion added specificity to the CT scan, but this situation occurred in only 3 patients. Early in the course of HSE, focal CT findings localized the temporal lobe of greatest involvement in 12 patients; 1 had a normal initial CT scan.
The temporal relationship of blood iodine levels to tumor enhancement in cranial computed tomography was studied in a series of patients. Both the bolus and biphasic techniques were evaluated. Peak tumor intensity may not develop immediately, but may be more pronounced on a 20-minute scan. The low-density centers seen in malignant gliomas show delayed enhancement. These low-density centers represent a second compartment which equilibrates with the intravascular and interstitial contrast material at a much slower rate. Patients with malignant gliomas can be scanned up to one hour following contrast injection without significant loss of information.
Computed tomography demonstrated areas of abnormal attenuation in the white matter in 14 patients with multiple sclerosis (MS). Nine were studied two or more times. Acute MS lesions exhibit decreased or normal attenuation without contrast enhancement and increased attenuation with it. On later scans these lesions show decreased attenuation with or without contrast material. Some lesions remain decreased in attenuation and some become normal both with and without contrast material.
Retrospective analysis of 25 pyogenic brain abcesses diagnosed by computed tomography (CT) revealed relatively specific morphologic characteristics of these infections. The ability to obtain an early accurate diagnosis resulted in a dramatic decrease in patient morbidity and mortality. Repeated examinations by CT permitted close monitoring of the response of the abscess to antibiotic therapy. In some instances the need for surgical intervention was eliminated or the surgical approach was modified as a result of these studies.
Comparison of different contrast dosages in adult patients with malignant gliomas studied by computed tomography indicates that 28-42 g of iodine is required for clinically diagnostic results. This can be translated into a 10 min iodine blood level of 100 mg/100 ml. Contrast doses in the range of 14 g of iodine are not satisfactory.
The application of wide aperture scanners to neuroradiology permits improved anatomic definition and localization of intracranial and intraorbital lesions. Coronal scans are most useful in demonstrating lesions of the skull base and apex, distinguishing between infra- and supratentorial lesions, and in determining if a lesion is intra- or extraaxial. Limitations of coronal scans include discomfort in positioning, high spatial frequency artifacts, and additional radiation exposure.