CM1

Q.  Match the following congenital malformations with the proper description from the list below:

A. 

Hydrocephalus

Cranioschisis

Telencephalic aplasia

Meningoencephalocele

Exencephaly

Lipomeningocele

Dicephalus

Diprosopus

Caudal occipital malformation

Holoprosencephaly-arrhinencephaly

Hydranencephaly

Lissencephaly

Diplomyelia

Diastematomyelia

Hydromyelia

Spinal cord segmental hypoplasia

Rachischisis

1. Failure of the cerebral hemispheres to form. 
2. Smooth brain without gyri and sulci
3. A fetus with two faces that typically have four nares and two complete jaws
4. Excess CSF accumulation within the brain. 
5. Atypical narrowing of the spinal cord, sometimes with only white matter present. 
6. Duplication of the spinal cord with the components sharing a single meningeal sheath
7. Brain tissue protruding outside of the cranium without skin covering. 
8. Cyclopian malformation. 
9. A calvarial opening on midline allowing the soft tissue structures to protrude externally.  
10. Failure of vertebral arch development; defined as several malformed (as in spina bifida) adjacent vertebrae. 
11. Two spinal cords, each with its own meningeal sheath and vertebral column.
12. Dilation of the central canal with CSF fluid. 
13. Fat-filled meningeal tissue protruding from a calvarial or vertebral midline defect.  The structure is covered by skin.
14. The meninges and brain tissue protrude through a calvarial midline defect.  The structure is covered by skin. 
15. The lack of cerebral parenchymal tissue.  The empty space is usually filled with CSF fluid covered by a thin pial-glial membrane and ependymal layer (from the compensatory expanded ventricles). 
16. Development of two complete brain structures that are conjoined caudally. 
17. A group of malformations affecting the back of the skull.  This may include rostral deviation of normal caudal occipital bone, absence of bone (often with a “keyhole shape), and replacement of normal bone with a fibrous sheet. 

A.

1. Telencephalic aplasia:  Failure of the cerebral hemispheres to form.  This may be caused by failure of the neurectoderm of the prosencephalon to separate from the skin ectoderm at the level of the rostral neuropore.  Folic acid deficiency in the mother and hyperthermia have been implicated in this defect development. 
2. Lissencephaly:  Smooth brain without gyri and sulci.  This is seen most often in Lhasa apso as a heritable defect.  A defect in neuronal migration causes thickening of the cortical tissue (pachygyria).  May be seen with cerebellar hypoplasia, so watch for this on the exam!  In humans it can be seen with episodes of intrauterine hypoxia and poor perfusion. 
3. Diprosopus:  A fetus with two faces that typically have four nares and two complete jaws.  There are usually three orbits with a malformed central eye.  There are four cerebral hemispheres, two diencephalons, and fusion of the brainstem/ cerebellar structures. 
4. Hydrocephalus:  Excess CSF accumulation within the brain.  Hydrocephalus can be described as internal, external, non-communicating, communicating, normotensive, hypertensive, compensatory, and obstructive. 
5. Spinal cord segmental hypoplasia:  Atypical narrowing of the spinal cord, sometimes with only white matter present. 
6. Diplomyelia:  Duplication of the spinal cord with the components sharing a single meningeal sheath.  The cord structures are commonly fused ventromedially.  The central canal may be absent or replaced by hydromyelia.
7. Exencephaly:  Brain tissue protruding outside of the cranium without skin covering. 
8. Holoprosencephaly-arrhinencephaly:  Cyclopian malformation.  These animals will have a single central eye, lack of olfactory structures, and a single prosencephalic structure that can be alobar, hemilobar, or lobar.  It is most common in lambs whose dams were exposed to Veratrum californicum on the 14^th or 15^th day of gestation.  The plant has cyclopamine that interferes with sonic hedgehog signaling in the prechordal plate.  This prevents the visual area from diving into two fields. 
9. Cranioschisis:  Also known as cranium bifidum.  A calvarial opening on midline allowing the soft tissue structures to protrude externally.  This is due to a failure of neural tube closure. 
10. Rachischisis:  Failure of vertebral arch development; defined as several malformed (as in spina bifida) adjacent vertebrae.  A myeloschisis includes failure of cord development as well along several spinal cord segments. 
11. Diastematomyelia:  Two spinal cords, each with its own meningeal sheath and vertebral column (may be joined by a bony wall). 
12. Hydromyelia:  Dilation of the central canal with CSF fluid.  Do not confuse with syringomyelia which is a posket of fluid separate from the central canal. 
13. Lipomeningocele:  Fat-filled meningeal tissue protruding from a calvarial or vertebral midline defect.  The structure is covered by skin.  Cause is unknown. 
14. Meningoencephalocele:  The meninges and brain tissue protrude through a calvarial midline defect.  This usually appears as a skin covered round, soft swelling outside the skull.  This problem can be seen in all species and the cause is usually unknown.  It has been seen as part of an inherited an inherited craniofacial anomaly in Burmese cats, and in one kitten occurred after the queen was treated with griseofulvin. 
15. Hydranencephaly:  The lack of cerebral parenchymal tissue.  The empty space is usually filled with CSF fluid covered by a thin pial-glial membrane and ependymal layer (from the compensatory expanded ventricles).  This is most often seen in viral diseases including Bluetongue (cattle and sheep), Bovine viral diarrhea (BVD, cattle), Cache Valley virus (cattle), Akabane virus (cattle), Aino (cattle), Chuzan (cattle).  Similar lesions (hypoplasia or aplasia) have been seen in the cerebellum with BVD virus in cattle and panleukopenia virus in cats (one case of a cat with hydranencephaly).  On poodle puppy had a focal unilateral hydranencaphly with defects affecting structures supplied by the middle cerebral artery.  In humans it can be seen with infections, teratogens, genetic defects in cerebral vasculature, and genetic defects in neuronal migration. 
16. Dicephalus:  Development of two complete brain structures that are conjoined caudally. 
17. Caudal occipital malformation:  A group of malformation affecting the back of the skull.  This may include rostral deviation of normal caudal occipital bone, absence of bone (often with a “keyhole shape), and replacement of normal bone with a fibrous sheet.  All situations involve crowding of the normal caudal occipital structures leading to numerous sequelae, the most common of which are varying degrees of cerebellar coning with syringohydromyelia and hydrocephalus. 

Veterinary Neuroanatomy and Clinical Neurology, 3^rd edition.  De Lahunta, Glass.  Saunders Elsevier 2009: pp 37-51.