According to a recent review in Neurosurgical Clinics of North America: Cerebral salt wasting (CSW) is a syndrome of hypovolemic hyponatremia caused by natriuresis and diuresis.
SIADH and CSW have similar urine chemistries, so the differentiation lies in volume assessment, which is often difficult. But distinction is important because the treatments differ. To further complicate matters, not all salt wasting syndromes are cerebral, leading to increasing popularity of the more general term renal salt wasting (RSW).
Related articles can be found here and here.