Arachnoiditis ossificans

Findings

Sagittal T1 (Figure 1) weighted MRI image of the lumbar spine with poorly defined nerve roots of the cauda equina. A bony fusion mass is noted posteriorly from prior remote bony fusion surgery.
Sagittal T2 (Figure 2) weighted image demonstrates heterogeneous mixed low T2 signal within the thecal sac at multiple levels.
Axial T1 (Figure 3) weighted image with poorly defined and "clumped" nerve roots.
Axial T2 (Figure 4) weighted image with heterogeneous mixed low T2 signal.
Axial noncontrast CT (Figure 5) image of the lumbar spine reveals extensive intrathecal calcification.
Sagittal reconstructed noncontrast CT (Figure 6) of lumbar spine demonstrates widespread intrathecal calcification and "clumped" nerve roots.


Diagnosis: Arachnoiditis ossificans


Arachnoiditis has many causes including prior surgery, myelographic contrast agents (especially oil-based contrast agents used in past), infection, subarachnoid hemorrhage, and inflammatory disease (ie, sarcoidosis). Lymphoma, carcinomatous meningitis, Guillain-Barre, and CMV radiculitis can also cause nerve root thickening. Chronic endstage archnoiditis results in arachnoiditis ossificans. Patients with arachnoiditis ossificans often have progressive neurologic deficits.

This case illustrates the importance of noncontast CT in evaluation of arachnoiditis ossificans, since MRI can demonstrate variable T1 and T2 signal characteristics.

Schizencephaly

Findings

There are bilateral complete clefts in the posterior frontal parietal regions, with the lateral ventricles communicating openly with the subdural space. These clefts are lined with gray matter (polymicrogyria). The septum pellucidum is absent, and the corpus callosum is hypoplastic.


Diagnosis: Schizencephaly


Schizencephaly is a disorder of neuronal migration during embryogenesis of the brain in which clefts extend from the lateral ventricles to the pia. These clefts are lined by gray matter, may be unilateral or bilateral, and range in size from small slits to large gaps in the surrounding cerebral hemisphere. The etiology is unknown, but its frequent association with other disorders, including heterotopic gray matter, dysplasia of the corpus callosum, and absence of the septum pellucidum, points to a common error in migration. Other associations include the presence of arachnoid cysts, mega cisterna magna, and calcifications (best seen on CT). Clinically, epilepsy has been reported in 50-80% of cases of schizencephaly, more commonly in association with unilateral than with bilateral clefts; but the seizures tend to begin earlier and have a worse outcome with bilateral defects. The most common clinical finding is of asymmetrical muscle tone, which ranges from asymptomatic to paraparesis; increasing severity is associated with frontal location and bilaterality of clefts. Delay in motor skills, language deficits (more common in temporal defects), and hydrocephalus are also frequently encountered. MR is the modality of choice for diagnosis and for differentiation from porencephaly. The key finding is that the cleft is lined by gray matter, which is pathognomonic for schizencephaly. Other disorders of migration that may demonstrate enlarged or joined ventricles include lissencephaly and holoprosencephaly.

Holoprosencephaly

Findings

Figure 1: The image shows a fetus with only a single cerebral ventricle. Its thalami are fused. The findings are suggestive of holoprosencephaly, especially alobar.
Figure 2:The image of the anterior face shows a single nostril suggesting a midfacial anomaly. Holoprosencephaly is often associated with midline facial anomalies.


Diagnosis: Holoprosencephaly


Holoprosencephaly is a malformation sequence involving the brain and often the face. It is a disorder of brain diverticulation resulting in partial or complete failure of cerebral hemisphere cleavage. Failure of cleavage results in failed formation of midline cranial structures. Midline brain development is associated with midface development and hence holoprosencephaly is associated with midface anomalies. Noncleavage of the primitive forebrain (the prosencephalon) leads to noncleavage in all planes. Associated olfactory and optic bulb anomalies occur because the prosencephalon, the primitive forebrain, does not cleave in a horizontal plane. A lack of proper cleavage in the transverse plane leads to improper formation of the telencephalon and diencephalon, which leads to abnormalities of thalamus and hypothalamus development. The often-seen fused or noncleaved thalami, as in the test case, may be a consequence. Finally, abnormal cleavage in a sagittal plane leads to abnormalities of the telencephalon, which normally forms the paired cerebral ventricles. In such patients an interhemisopheric fissure and other midline structures will not exist. The anomaly develops between the fourth and eighth week of embryonic life, well before the structures of the fetal brain can be adequately imaged by antenatal US. The abnormality is found in 1 in 16,000 live births, but in a larger number of fetuses and an even larger number of embryos (as high as 1 in 250), many of whom do not survive the pregnancy, hence affecting the numbers found among living births. There is a 12% recurrence rate for nonchromosomal cases.

Cases of holprosencephaly are divided into 3 forms. The most severe form, alobar holprosencephaly, typically results in a single holosphere (rather than 2 brain hemispheres), a single ventricle which often communicates with a dorsal sac, and fused thalami. There is no third or fourth ventricle, falx, corpus callosum, or interhemispheric fissure. The midbrain, brainstem, and cerebellum are typically normal unless made hypoplastic by mass effect of the large monoventricle or dorsal sac.

The intermediate form, ie, semilobar holoprosencephaly, shows at least partial prosencephalon cleavage. Temporal and occipital lobes may be separated. There may be a rudimentary interhemispheric fissure or a posterior falx. The incomplete form of holoprosencephaly, known as lobar holoprosencephaly, is the least devastating and may have a relatively normal appearing brain. There may simply be an absent septum pellucidum with an evident corpus callosum and perhaps fused or squared frontal horns. Rostral fusion may be the only ventricular abnormality with atria, occipital horns and temporal horns apparently normal.

When a child is born with a midline facial anomaly, a head US is performed to rule out holoprosencephaly. Facial abnormalities in cases of holoprosencephaly are variable. There may be none, or mild dysmorphism, such as hypotelorism or bilateral median cleft lip or palate. Cebocephaly, an intermediate form, has hypotelorism and a single nostrilled nose. Ethmocephaly is a more severe form of facial anomaly with severe hypotelorism, arhinia, and an interorbital single or double proboscis. Other severe abnormalities include cyclopia with variable eye and nose pairings. More significant facial anomalies are almost always associated with alobar holoprosencephaly.

Holprosencephaly is usually a terrible diagnosis no matter what its form. Those with severe brain abnormality, especially with arhinia or choanal atresia, die soon after birth if they survive the pregnancy. Less severely affected individuals may live several years but usually have severe neurologic and intellectual impairment. Even those with lobar holoprosencephaly who may live a normal lifetime may be severely retarded.