Absent septum pellucidum

Dr Maxime St-Amant ◉ and Dr Henry Knipe ◉ ◈ et al.

An absent septum pellucidum may rarely be an isolated finding, or more commonly be seen in association with a variety of conditions.

Cavum septum pellucidum is always visualized between 18 and 37 weeks and within a biparietal diameter of 44 to 88 mm. Failure to detect the cavum septum pellucidum within this time interval requires further investigation. However, the absence of cavum septum pellucidum on the ultrasound exam prior to 18 weeks or later than 37 weeks is considered a normal finding.

Developmental

Acquired

Radiographic features

Non-visualization of the septum pellucidum with direct communication of the frontal horns. Additionally, the following characteristics may be seen ³:

boxing/squaring off of the frontal horns
inferior pointing frontal horns
abnormally inferiorly positioned fornix (coronal views)

References

Malformations of the central nervous system

malformations of cortical development
- abnormal cell proliferation or apoptosis
  - abnormal brain size
    - microcephaly
      - with normal to simplified cortical pattern
      - microcephaly with lissencephaly
      - microcephaly with extensive polymicrogyria
    - macrocephalies (megalencephaly/macrocephaly)
  - abnormal cell proliferation
    - non-neoplastic
      - cortical hamartomas of tuberous sclerosis
      - hemimegalencephaly
      - focal cortical dysplasia (Type I and Type IIb)
        
        Palmini classification (2004)
        
        Barkovich classification (2005)
        
        Blumcke classification (2011)
    - neoplastic
  - abnormal neuronal migration
    - lissencephaly
      - lissencephaly type I: subcortical band heterotopia spectrum (band heterotopia): undermigration
      - lissencephaly type II (cobblestone complex)
    - heterotopia: ectopic migration
      - subependymal heterotopia
      - subcortical heterotopia (not including band heterotopia)
      - marginal glioneuronal heterotopia
  - abnormal cortical organization
    - mild malformations of cortical development (previously microdysgenesis)
    - polymicrogyria and schizencephaly
      - bilateral polymicrogyria syndromes
      - schizencephaly
    - focal cortical dysplasia (Type IIa)
- not otherwise classified
  - malformations secondary to inborn errors of metabolism
    - mitochondrial and pyruvate metabolic disorders
    - peroxisomal disorders
  - other unclassified malformations
    - sublobar dysplasia
midline abnormalities of the brain
- absent septum pellucidum
- cephaloceles
- midline nasal region lesions
  - nasal dermoid
  - nasal glioma
  - nasal dermal sinus
- cerebral hemispheres
  - holoprosencephaly/septo-optic dysplasia spectrum
    - septo-optic dysplasia
    - lobar holoprosencephaly
    - semilobar holoprosencephaly
    - alobar holoprosencephaly
    - middle interhemispheric variant/syntelencephaly
- corpus callosum
  - corpus callosum agenesis/dysgenesis
    - racing car sign
- intracranial lipoma
malformations of the cerebellum
- cerebellar hypoplasia
  - focal hypoplasia
  - generalized hypoplasia
    - with enlarged fourth ventricle
      - Dandy-Walker continuum
        
        Dandy-Walker malformation
        
        Dandy-Walker variant
        isolated inferior vermian hypoplasia
        
        Blake’s pouch cyst
        
        fourth ventriculocoele
    - normal fourth ventricle
      - with normal pons
      - with small pons
        normal foliation
        
        pontocerebellar hypoplasias of Barth, types I and II
        
        cerebellar hypoplasias, not otherwise specified
- cerebellar dysplasia
  - focal dysplasia
    - isolated vermian dysplasia
      - molar tooth malformations including Joubert syndrome
      - rhombencephalosynapsis
    - isolated hemispheric dysplasia
      - focal cerebellar cortical dysplasias/heterotopia
      - Lhermitte-Duclos-Cowden syndrome
  - generalized dysplasia
    - congenital muscular dystrophies
    - cytomegalovirus
    - lissencephaly with RELN mutation
    - lissencephaly with agenesis of corpus callosum and cerebellar dysplasia
    - associated with diffuse cerebral polymicrogyria
    - diffusely abnormal foliation
malformations of the brainstem