The degree to which the processes involved in visual perception and visual imagery share a common neuroanatomical substrate is unclear. Physiological evidence for localization of visual imagery early in the visual pathways would have important bearing on current theories of visual processing. A magnetic resonance imaging technique sensitive to regional changes in blood oxygenation was used to obtain functional activation maps in the human visual cortex. During recall of a visual stimulus, focal increases in signal related to changes in blood flow were detected in Vl and V2 cortex in five of seven subjects. These experiments show that the same areas of the early visual cortex that are excited by visual stimulation are also activated during mental representation of the same stimulus. Some of the processes used in topographically mapped cortical areas during visual perception may also be utilized during visual recall.

Children with primary tuberculosis infection without disease must be identified and treated preventively to avoid an increase in the incidence of tuberculosis in children. However, the recognition of infected cases without disease is often difficult. In particular, minimal active disease may be present in many cases but unrecognised on chest radiography. Computed tomography was therefore performed in 15 children with tuberculous infection and a normal chest radiograph to measure the size oftheir mediastinal lymph nodes. Ten control children without tuberculosis were also evaluated. When compared with controls it was found that nine of 15 (60%1/o) infected children had enlarged lymph nodes. Adenopathies were more frequent in infected children less than 4 years old than in those over 8 years old. The demonstration of unrecognised active disease in many infected children raises the question of the adequate treatment for these children. It is proposed that a two drug regimen would be more appropriate than isoniazid alone in these cases. (Arch Dis Child 1993; 69: 430-432) H6pital des Enfints Malades,

Synovial hypertrophy, effusion, and articular cartilage status were evaluated with gadolinium tetraazacyclododecanetetraacetic acid (DOTA)-enhanced magnetic resonance (MR) imaging in 24 knees in 24 pediatric patients (17 female, seven male; mean age, 10 years; range, 3-18 years) with juvenile rheumatoid arthritis (JRA). T1-weighted spin-echo sequences were performed with a 0.5-T unit before and immediately after injection of Gd-DOTA (0.1 mmol/kg). Substantial enhancement of synovial proliferation was seen in 23 of 24 knees, allowing precise assessment of pannus extension (n = 23), joint effusion (n = 21), cartilage loss (n = 21), and meniscal hypotrophy (n = 23). On T1-weighted images without contrast enhancement, cartilage thickness, loculation of joint effusion, and pannus extension were underestimated. Thus, Gd-DOTA-enhanced MR imaging is mandatory in the assessment of knee involvement in children with JRA and may prove to be useful in the evaluation of response to therapy.

In order to evaluate the role of gadolinium-DOTA enhanced MRI in the management of painful osseous crises in children with sickle cell anemia (SCA), nine children with SCA underwent MRI, bone scans and ultrasonographic studies during 11 osseous crises. Imaging findings were compared with the final diagnosis: three acute osteomyelitis (AO) and 16 acute infarcts (AI). MRI could not differentiate AO from AI. The appearance of severe AI was very misleading and was similar to the usual appearance of AO, including soft tissue changes, periosteal reaction and patterns of enhancement. Gadolinium-DOTA enhanced MRI was useful for determining the anatomic site and extent of AO or AI and for distinguishing between necrotic material, fluid collection and vascularized inflammatory tissue. It can also help to guide the aspiration of intraosseous, subperiosteal and soft tissue fluid collections.