Absent septum pellucidum

Case contributed by Bruno Di Muzio
Diagnosis certain



Patient Data

Age: 42-year-old
Gender: Male

CT Brain


Technique: Non-contrast images obtained through the brain.

Findings: The septum pellucidum is not clearly visualized. No evidence of fusion of thalami or absence of the corpus callosum. The optic nerves are present.

Moderate rounding of the frontal horns of the lateral ventricles is present with upward bowing of the thinned corpus callosum and a 15mm x 9 mm low density lesion in the region of the pineal gland possibly compressing the aqueduct of Sylvius and obstructing CSF flow. No transependymal edema to suggest acute obstruction.

No intra or extra-axial hemorrhage, collection or parenchymal contusion. Subtle hyperdensity in the posterior aspect of the middle cranial fossae bilaterally most likely relates to beam hardening artefact rather than traumatic contusion.

Dense 5mm focus of plaque-like calcification seen along the lateral wall of the left cavernous sinus may be related calcified meningioma.

No skull vault or base of skull fracture.

Right parietal scalp hematoma

Conclusion: No evidence of traumatic brain injury. Apparent absence of the septum pellucidum raises the possibility of mild abnormality in the spectrum of lobar holoprosencephaly/septo-optic dysplasia and congenital midline malformation.15 x 9 millimeter low density pineal gland lesion with fourth ventricular dilatation raises the possibility of chronic hydrocephalus which may produce a fenestrated appearance to the septum pellucidum. 5 mm focus of calcification involving the lateral wall of the left cavernous sinus may reflect dural calcification associated with a meningioma.

Clinical correlation and further the MRI imaging may help delineate the above findings.

MRI Brain


Technique: Multiplanar, multisequence images were acquired including volumetric T1 weighted images and post-contrast images.

Findings: The septum pellucidum is noted to be absent and there is a flattening of the roof of the anterior horns of the lateral ventricles. The optic chiasm is not small and no features to suggest a lobar holoprosencephaly. No schizencephaly, cortical dysplasia or gray matter heterotopia.

The ventricles are the fourth and third ventricles are slightly large, but no transependymal edema to suggest this might represent acute hydrocephalus. The cerebral aqueduct is narrowed by a cystic structure in the pineal gland measuring 14 x 15 x 13 mm, which has thin internal septations within it.

The calcified focus in the left cavernous sinus is better assessed on the CT and is shown on MR as a focus of susceptibility artefact at this site of dubious clinical significance. No mass lesion identified at this site.

No parenchymal susceptibility artefact.

Conclusion: Absent septum pellucidum, but no features to suggest a lobar holoprosencephaly and the optic chiasm is not small to suggest a septo-optic dysplasia. Cystic pineal lesion, probably a pineal cyst, however, the thin internal septations and size means follow up imaging is probably warranted to exclude a pineocytoma. The lateral and third ventricles are slightly dilated, which could be due to narrowing of the cerebral aqueduct by the cystic pineal lesion.​

Case Discussion

This case illustrates an absent septum pellucidum and a minimally complicated pineal cyst (measuring more than 10 mm and showing some internal septa) that compress the tectal plate and narrows the cerebral aqueduct. There is no evidence of other cerebral malformation associated with the absent septum pellucidum. 

As the patient is asymptomatic and all those findings were incidentally found, an MRI follow-up was proposed for surveillance of the pineal cyst. 

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