[X-ray computed tomographic aspects of benign primary cerebral melanomas. Apropos of 4 cases]. / Aspects tomodensitométriques des mélanomes bénins primitifs cérébraux. A propos de 4 observations.

Benign primitive melanomas are rare tumours usually involving the leptomeninges. Four cranial localizations are reported: 2 tumours of the foramen magnum, 1 of the cerebellopontine angle and 1 supratentorial. The clinical symptomatology is variable according to the level. Slow medullary compression is frequent. One can emphasize the special and difficult problem of foramen magnum tumours that present with a very variable clinical status frequently simulating a non surgical disease of the central nervous system. The benign and primitive appearance of these tumours is evocated by the slow and favourable evolution and by the absence of extraneurologic melanotic tumour. Our purpose is essentially to emphasize the radiological and particularly the computed tomographic (CT) findings poorly described in the literature. Benign melanomas have resemblance with meningiomas: osseous or meningeal relationship, homogeneity and high density. On the other hand the angiography shows poor vascularization. One can think that a tumor simulating a meningioma by CT but not by angiography is perhaps a benign melanoma. The special problem of the radiological diagnosis of foramen magnum tumours is evocated: Computed myelography, tridimensional imaging by NMR.

[Pelvimetry by digitalized radiography]. / Pelvimétrie par radiographie numérisée.

We studied the ability of digital radiographs generated on a computed tomography scanner to replace conventional pelvimetry. Two digital radiograph's and one CT section permit us to measure the maternal pelvis. The anteroposterior digital radiograph allows measurement of the maximum transverse and median transverse diameters of the pelvic inlet. These two distances are corrected for magnification after reference to the lateral digital radiograph and to a graph determined owing to a phantom. The anteroposterior digital radiograph also permits to perform a CT section passing through the ischial spines with direct measurement of the inter spinous diameter. The lateral digital radiograph gives us the true values for the anteroposterior diameter of the pelvic inlet, the low sagittal diameter, the cord and the rise of the sacrum. The dosimetry studies demonstrated that maternal skin doses and fetal gonad doses were very low. Pelvimetry using digital radiography is a simple and rapid to perform procedure which offers the advantage of low radiation exposure to both fetus and mother and a high accuracy of measurement.

Pelvimetry by digital radiography.

We studied the ability of digital radiographs generated on a computed tomography scanner to replace conventional pelvimetry. Two digital radiographs were usually sufficient to measure the maternal pelvis. The antero-posterior (AP) digital radiograph allowed measurement of the transverse diameter of the pelvic inlet, the interspinous distance and the intertuberous diameter. These three distances were corrected for magnification after reference to the lateral digital radiograph. The lateral radiograph gives the AP diameter of the pelvic inlet and the low sagittal diameter. Dosimetry studies demonstrated that maternal skin doses and fetal gonad doses were very low. Pelvimetry using digital radiography is a simple procedure which offers the advantage of low radiation exposure to both fetus and mother and a high accuracy of measurement.

The role of computed tomography in the assessment and treatment of acetabular fractures.

The assessment of acetabular fractures by conventional radiology is difficult whilst essential to the planning of orthopaedic treatment. This report details the results of computed tomography (CT) in a study of acetabular fractures in 30 patients. Computed tomography was always superior to conventional radiology, particularly in the evaluation of lesions of the posterior acetabular margin. The standard classification of the fractures did not require modification but was reinforced by the three-dimensional visualisation of the lesions. The particular contribution of CT was in the assessment of associated lesions often not apparent on conventional views of the pelvis: these comprised sacroiliac lesions in 60% of cases, intra-articular loose bodies in 33% of cases and pelvic haematomas in 17% of cases. As a result of CT, treatment was changed in one third of cases. In addition to its role in indicating the need for surgical or orthopaedic treatment, CT sometimes permitted a better choice of surgical technique, especially in respect of sacroiliac lesions causing as yet unexplained sciatica.

Optic nerve head drusen. High-resolution computed tomographic approach.

Optic nerve head drusen are rare, inherited concretions, which are almost always calcified; their appearance must be known because they represent one of the major causes of pseudopapilledema. The computed tomographic (CT) scan can show small and buried drusen, which are sometimes difficult to diagnose by the ophthalmoscopic examination. Four cases of drusen (two bilateral and two unilateral) were confirmed or diagnosed by high-resolution CT. The CT appearance of drusen is characteristic because the calcifications are well defined, punctate, and strictly located in the optic disc. The use of high-resolution CT scanners is very helpful.

Retinitis pigmentosa associated with astrocytic hamartomas of the optic disc.

A case of retinitis pigmentosa associated with astrocytic hamartomas of the optic disc is described. The rarity of tuberous sclerosis in this association is discussed, as well as differences between optic nerve head drusen and astrocytic hamartomas ('giant drusen') which can both be associated with retinitis pigmentosa.