Teaching Case

Facial angiofibroma, seizures, and developmental delay.

The patient had facial angiofibroma, seizures, and developmental delay. Dermal depigmented nevi, and multiple subungual fibromas were noted. A CT scan obtained elsewhere revealed a calcified, subependymal nodule, and a hypodense lesion in the right frontal region. The patient was referred to MRI. Besides conventional MR imaging sequences, echo-planar diffusion imaging was performed utilizing the 'trace-diffusion' sequence with TR=5700, and TE=139.03 msec.

The main cerebral lesions of tuberous sclerosis include calcified subependymal hamartomas, parenchymal (cortical and white matter) hamartomas, and rarer giant cell tumors. Diffusion imaging, a relatively new MR sequence, is dependent on the mobility of water molecules, and provides data on tissue integrity. This sequence has mainly been used for evaluation of acute ischemia, and its differention from vasogenic edema. If the mobility of water molecules is restricted such as in ischemia (cytotoxic edema) high signal is observed on diffusion imaging at b=1000 sec/mm2 (low signal on corresponding ADC maps). In the presence of vasogenic edema high signal is seen on ADC maps. However, this is apparently lower than CSF, as diffusion coefficents are very high in fluids where diffusion is free. In a recent study calculated mean ADC values for cytotoxic edema, vasogenic edema, and CSF were: 0.32±0.09 X 103 mm2/sec, 1.68±0.27 X 10-3 mm2/sec, and 3.40±0.45 X 10-3 mm2/sec, respectively (R.N. Sener, unpublished data, 2000). In the current patient with tuberous sclerosis the ADC value of a right frontal hamartoma was 1.31 X 10-3 mm2/sec, indicating an increased molecular motion comparable to vasogenic edema. It was interesting that the true diffusion image (b=1000 sec/mm2 image) was negative for the hamartoma, while the ADC map showed it with high signal, and with abovementioned ADC value.