The lissencephaly-pachygyria spectrum is useful in describing the spectrum of diseases that cause relative smoothness of the brain surface and includes:
- agyria: no gyri
- pachygyria: broad gyri
- lissencephaly: smooth brain surface
Lissencephaly-pachygyria can be further divided into types I (classic) and type II, which differ in clinical presentation, underlying genetic abnormalities, and both microscopic and macroscopic (including imaging) appearances 2,6. They themselves represent a heterogeneous group of disorders. This article highlights a few generalities and outlines the differences between the two types, which are otherwise discussed separately:
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Type I (classic) lissencephaly typically presents with marked hypotonia and paucity of movement.
Although lissencephaly can be identified on all cross-sectional modalities (antenatal and neonatal ultrasound, CT and MRI), MRI is the modality of choice to fully characterise the abnormalities.
Type I and type II lissencephaly demonstrate vaguely similar appearances (thus the common term lissencephaly) but different macroscopic and imaging appearances are visible.
Type I (classic) lissencephaly can appear as the classic hour glass or figure-8 appearance or with a few poorly formed gyri (pachygyria) and a smooth outer surface. It is usually associated with band heterotopia.
Type II lissencephaly on the other hand has a microlobulated surface referred to as a cobblestone complex. Band heterotopia is not evident and the cortex is thinner than in type I.
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- 3. Allanson JE, Ledbetter DH, Dobyns WB. Classical lissencephaly syndromes: does the face reflect the brain? J. Med. Genet. 1998;35 (11): 920-3. J. Med. Genet. (link) - Free text at pubmed - Pubmed citation
- 4. Barkovich AJ, Kjos BO. Gray matter heterotopias: MR characteristics and correlation with developmental and neurologic manifestations. Radiology. 1992;182 (2): 493-9. Radiology (abstract) - Pubmed citation
- 5. Abdel razek AA, Kandell AY, Elsorogy LG et-al. Disorders of cortical formation: MR imaging features. AJNR Am J Neuroradiol. 2009;30 (1): 4-11. doi:10.3174/ajnr.A1223 - Pubmed citation
- 6. Volpe JJ. Neurology of the newborn. W B Saunders Co. (2008) ISBN:1416039953. Read it at Google Books - Find it at Amazon