We present an illustration of the spectrum of intracranial abnormaliti
es associated with absence of the septum pellucidum to better define a
nd illustrate this disorder. CT and 1.5 Tesla MRI examinations of fift
een Patients with absence of the septum pellucidum were meticulously a
nalyzed and correlated with clinical and laboratory studies. The findi
ngs were compiled and categorized based upon the presence and type of
associated radiologic abnormalities. Absence of the septum pellucidum
may occur as an isolated abnormality (n = 3). In most patients (n = 12
), associated complex developmental abnormalities are present which in
clude heterotopias, hypoplastic falx, ventricular clefts, encephalocel
e, small pituitary gland, small optic nerves and chiasm, and corpus ca
llosal dysgenesis. Inferior pointing and a squared-off appearance of t
he frontal horns are frequently noted. These, or other, more severe ve
ntricular configuration deformities are present in all patients. We ha
ve portrayed the complete range of findings associated with absence of
the septum pellucidum using an illustrative approach to clarify the d
ifferent patterns of radiologic abnormalities which may be seen with t
his complex entity.