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:
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 hourglass 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.
History and etymology
Lissencephaly is derived from the Greek word λισσος (lissos), meaning smooth 7.
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- 2. Pilz DT, Quarrell OW. Syndromes with lissencephaly. J. Med. Genet. 1996;33 (4): 319-23. J. Med. Genet. (link) - Free text at pubmed - Pubmed citation
- 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
- 7. Ian Brookes. The Chambers Dictionary. (2018) ISBN: 9780550101853