Polymicrogyria

Findings

Figure 1, Figure 2, and Figure 3: CT scans of the brain reveal macrocephaly with an abnormal gyral and sulcal pattern.
Figure 4, Figure 5, and Figure 6: Multiple axial T2 MR images reveal macrocephaly and polymicrogyria. There are excessive small convolutions of the cortex with an undulating cortical pattern. The white matter signal is increased, consistent with immature myelination. Note the right parietal shunt catheter with normal ventricular size.
Figure 7, Figure 8, and Figure 9 : There is loss of normal gyral architecture, thickened cortex (isointense to gray matter) and indistinct gray-white interface. This pattern is diffuse and is present throughout the brain.


Diagnosis: Polymicrogyria


Polymicrogyria is a disorder of late neuronal migration and cortical organization. The neurons migrate to the cortex but distribute abnormally resulting in the formation of multiple small undulating gyri. This is believed to result secondary to ischemic laminar necrosis of the fifth cortical layer after 20 weeks gestation at which time the cortical neurons have migrated to the brain surface. Other intrauterine vascular insults or infections, including CMV, may also result in this disorder. Multiple gene loci have been shown to result in polymicrogyria as well.

The result of this late neuronal migration disorder is an excessive number of small disorganized cortical convolutions with a thickened cortex. The white matter thickness is usually normal. CT findings consist of excessive small convolutions. These small folds of cortex may resemble pachygyria (incomplete lissencephaly) which results in sparse, broad, flat gyri. In order to best characterize the cortex, MRI is usually performed. Findings on T1 weighted imaging include irregular cortex isointense to gray matter with an indistinct cortical white matter surface. On T2 weighted imaging, two imaging patterns may be present depending on the age of the patient. In infants under 12 months, T2 weighted imaging reveals small, fine undulating cortex with normal 3-4mm thickness. In infants older than 18 months, the cortex is thick and bumpy (6-8 mm) and may contain hypomyelination and cortical infolding. Periventricular calcification may be present if the disorder is caused by TORCH infection, such as CMV.

Polymicrogyria may be regional or diffuse. Congenital bilateral perisylvian syndrome is the most common manifestation of polymicrogyria. This results in polymicrogyria of the opercular cortex with abnormal sylvian fissure sulcation. Polymicrogyria is present in multiple syndromes, including Zelleweger syndrome and Fukuyama muscular dystrophy. These syndromes contain polymicrogyria as well as other clinical and laboratory findings.

The diagnosis of polymicrogyria is descriptive and does not describe the underlying etiology. Clinically, patients may present in the neonatal period or later in infancy with developmental delay, spasticity, seizures and global developmental delay that may result in feeding difficulties, respiratory abnormalities, motor dysfunction and mental retardation.

Ameloblastoma

Findings

CT images demonstrate an expansile cystic “bubbly” mass within the right mandibular body and extending into the ramus. Thin bony septations are seen within the lesion (Figure 1 and Figure 2). Marked thinning of the cortical margins is noted with focal areas of dehiscence (Figure 3). The margins are relatively well-defined with no significant infiltration of adjacent soft tissues. The tongue and medial soft tissue structures are displaced and pushed by this large soft tissue mass in the mandible (Figure 4).
Ill-defined enhancement is seen in the anteromedial aspect of the mass on postcontrast CT (Figure 5).


Diagnosis: Ameloblastoma


Ameloblastoma is a histologically benign, locally aggressive tumor arising from the odontogenic ectoderm. It arises from the enamel-forming cells of the odontogenic epithelium that have failed to regress during embryonic development. Ameloblastoma is the most common odontogenic tumor (representing 10% of all tumors in the maxillomandibular region).

The tumor most commonly occurs in the posterior mandible, typically in the third molar region, with associated follicular cysts or impacted teeth. The mandible is affected four times more frequently than the maxilla. Patients typically present in the third to fifth decades of life with a slow-growing, painless mass.

Ameloblastoma typically presents as a mixed cystic-solid mass in the posterior mandibular ramus associated with an unerupted 3rd molar tooth. The expansile, radiolucent tumor can be unilocular (20%) or multilocular (80%), with a characteristic "soap bubble–like" appearance. The slow growth of the tumor can lead to significant expansion of the mandible with an osseous shell that represents involved bone. The tumor can perforate the lingual cortex and spread to adjacent soft tissues. Erosion of the roots of adjacent teeth is unique to ameloblastoma and indicates aggressive behavior of the tumor.

MRI best defines the extra osseous extension and shows the multilocularity, mixed solid and cystic components, irregularly thickened walls, papillary projections, and marked enhancement of the walls and septa. Presence of nodular enhancement distinguishes ameloblastoma from large dentigerous cyst and odontogenic keratocyst.

The treatment of ameloblastoma is surgical excision with wide free margins. Appropriate reconstruction may be performed at the same time. Solid lesions show high recurrence rates (50% to 90%), necessitating tumor excision or partial resection of the jawbone. Although malignant transformation is rare (1%), repeated recurrences increase the likelihood of malignancy.

Methanol intoxication

Findings

Figure 1: Unenhanced CT of the head demonstrates acute hemorrhage within the left caudate nucleus as well as layering in the left lateral ventricle.
Figure 2: There is diffuse edema with effacement of the sulci, white matter lucency, and punctate hemorrhage of the putamina.

Differential diagnosis (Acute)
- Toxic: Methanol intoxication, Carbon monoxide, Cyanide, Hydrogen sulfide
- Hypertensive intracranial hemorrhage
- Hypoxia
- Hypoglycemia
- Hemolytic-uremic syndrome

Differential diagnosis (Chronic)
- Mitochondrial encephalopathies (Leigh’s disease, MELAS, Kearns-Sayre, etc.)
- Leukodystrophy
- Wilson disease


Diagnosis: Methanol intoxication


Methanol is commonly found in household products such as windshield wiper fluid, paint remover, and antifreeze. It is an uncommon but potentially fatal cause of toxicity, and a high clinical suspicion must exist. Symptoms of visual disturbance (blurriness, blindness), headache, nausea, dizziness and confusion may present 12 to 24 hours after consumption. The symptomatic delay is due to the time it takes the liver to metabolize methanol. The gastrointestinal tract rapidly absorbs methanol. It is converted by alcohol dehydrogenase to formaldehyde. The formaldehyde is then converted to the toxic metabolite formic acid by aldehyde dehydrogenase. Formic acid and the resulting metabolic acidosis are thought to contribute to the intracranial findings of cerebral edema, putaminal necrosis, and potential basal ganglia hemorrhage. The basal ganglia have a high metabolic demand and a rich vascular supply, which are thought to be more susceptible to toxic metabolites and hypoxia.

Management and prognosis are based on the resulting metabolic acidosis. Intravenous fomepizole is administered to competitively inhibit alcohol dehydrogenase. This is preferred over the traditional administration of intoxicating intravenous ethanol. Further treatment includes hemodialysis to remove unmetabolized methanol and sodium bicarbonate to treat the metabolic acidosis. Patient prognosis is poor in the setting of basal ganglia hemorrhage. Unfortunately, despite optimal treatment, our patient expired within four days of consuming nearly half-a-gallon of windshield wiper fluid.

Pineoblastoma

Findings

Axial CT scan at the level of third ventricle demonstrates a well-defined hyperdense mass in relation to the posterior third ventricle showing peripheral calcification (Figure 1).
Figure 2 demonstrates hydrocephalus with transependymal flow seen as confluent low attenuation in the periventricular regions.
The fourth ventricle is normal in size (Figure 3).
The mass demonstrates minimal, heterogeneous, increased signal on the T2-weighted image (Figure 4) as well as heterogeneous enhancement on postcontrast images (Figure 5). Sagittal postcontrast T1-weighted image (Figure 6) demonstrates mass effect on the midbrain tectum, which is displaced inferiorly. The internal cerebral veins are seen as tubular enhancing structures superior to the lesion (Figure 7).


Diagnosis: Pineoblastoma


Pineal region tumors are uncommon, but are more often seen in children compared with adults. Germinomas and astrocytomas account for the majority of pineal region masses. Pineal parenchymal tumors constitute less than 15% of pineal neoplasms. Pineoblastomas are highly malignant, primitive neuroectodermal tumors of the pineal gland that are typically found in children 2 to 3 years of age. Pineocytomas, on the contrary, are slow growing pineal parenchymal tumors of adults.
Patients usually present with signs of elevated intracranial pressure, ataxia and/or Parinaud’s syndrome (palsy of the upward gaze, dissociation of light and accommodation, and failure of convergence). Unlike germ cell tumors, there is no elevation of serum tumor markers in pineal parenchymal tumors.
Pineoblastomas are WHO Grade IV tumors that are poorly marginated, demonstrate peripheral calcification, as well as hyperdensity and heterogenous enhancement of the solid components. Peritumoral edema is characteristically mild. In contradistinction, germinomas demonstrate central “engulfed” calcification and uniform enhancement. Both pineoblastomas and germ cell tumors can demonstrate CSF dissemination.
The treatment for pineoblastoma includes surgical ressection, cranio-spinal radiation, as well as chemotherapy. The prognosis is dismal in most cases.
In “trilateral retinoblastoma”, pineoblastoma may develop in patients with familial and/or bilateral retinoblastoma.

Spinal dural arteriovenous fistula

Findings

Figure 1, Figure 2, and Figure 3: Sagittal T2 images of the spine demonstrate low signal tortuous vessels in the posterior epidural space.
Figure 3: Sagittal T2 image demonstrates abnormal high signal within the lower cord consistent with myelopathy. The level of myelopathy does not necessarily correlate with the level of the fistula.


Diagnosis: Spinal dural arteriovenous fistula


The term “spinal vascular malformation” is a general term that encompasses a variety of spinal vascular lesions. In 2002, Spetzler et al. proposed a revision to the prior I-IV classification system that is more descriptive and functional. Spetzler categorizes vascular lesions as neoplastic, aneurysms, and abnormal communications between arteries and veins. The last category can be further subdivided into arteriovenous malformations and arteriovenous fistulas, with even further subclassification based upon location within the spinal canal. Arteriovenous malformations can be extramedullary-intramedullary and/or intramedullary. Arteriovenous fistulas can be extradural or intradural (dorsal or ventral).

Intradural dorsal arteriovenous fistulas are the most common type of spinal AV fistula and are thought to be acquired. AVFs represent an abnormal communication between a spinal radicular artery and a medullary draining vein. Over time, the high pressure of the artery communicating with the draining vein creates a functional obstruction to venous flow, resulting in spinal venous engorgement and hypertension. Clinically, this manifests as progressive myelopathy. The typical patient with a spinal AVM or AVF is usually a male over 40 that presents with progressive lower extremity weakness and bowel and bladder difficulties.

There are several imaging findings in patients with spinal dural AVFs. Specifically, MRI demonstrates dilated spinal veins as tiny flow voids within the intradural compartment. Most dural fistulas are located in the lower thoracic and lumbar spinal levels, with associated increased T2 signal within the cord secondary to myelopathy from venous congestion. Note however that the location of the dilated veins and myelopathy does not always correlate with the level of the fistula.

The use of spinal MR angiography in evaluating patients prior to conventional catheter angiography of the spine has become a hot topic in recent years. Advantages that have been discussed include the decreased contrast load and radiation exposure because the angiographer can perform a targeted diagnostic and possibly therapeutic procedure. Even more recently, CT angiography has been employed in a similar role.

Treatment of dural fistulas is tailored to the functional anatomy of the vascular malformation. Treatment options include embolization, which can be therapeutic or pre-surgical, and surgical resection.

Wormian bones

Findings

There are numerous wormian bones (Figure 1, Figure 2, Figure 3, Figure 4, Figure 5, and Figure 6).
Wormian bones are within the sagittal suture (Figure 4) and the lambdoid sutures (Figure 5).
There is a metopic suture, which is an accessory frontal bone suture (Figure 4).


Diagnosis: Wormian bones


Wormian bones are secondary ossification centers within sutural lines. These characteristic locations should allow differentiation from fractures.
They occur most frequently in the lambdoid suture. They may present in normal infants up to the age of one year, and may be single or multiple. Associated pathologic entities include osteogenesis imperfecta, cleidocranial dysplasia, and hypothyroidism.
Other associations include pyknodysostosis, Down syndrome, progeria, hypophosphatasia, pachydermoperiostosis, otopalatodigital syndrome and Menke’s kinky hair syndrome.
This patient had normal variant Wormian bones without an associated diagnosis.

Hemangioblastoma

Findings

There is a right parasagittal lesion along the medial aspect of the cerebellum. The cystic mass has pronounced mass-effect on the dorsal brainstem and tectum. Extending from the cyst wall along one of the septations is an enhancing nodule.

Differential diagnosis:
- Hemangioblastoma (given patient age, the most likely diagnosis)
- Medulloblastoma
- Pilocytic astrocytoma


Diagnosis: Hemangioblastoma


Key points

The hemangioblastoma (HB) is a vascular neoplasm of unknown etiology. Cerebellar hemangioblastoma is the most common primary brain neoplasm involving the infratentorial space in adults. This benign tumor is readily curable by surgery. More than 85% of hemangioblastomas occur in the cerebellum, with the remainder occurring in the spinal cord, medulla, and cerebrum in a 4:2:1 ratio. Approximately 10% of posterior fossae masses are hemangioblastomas. Men are more commonly affected than females, and patients are usually young adults. The common symptoms are headache, nausea, vomiting, ataxia, and vertigo. In 40% of patients, polycythemia is present secondary to increased erythropoietin produced by the tumor (more common in solid tumors). A spinal hemangioblastoma may present with subarachnoid hemorrhage.

The classic findings of an HB are that of a cystic mass with a solid mural nodule (60% of cases), which is highly vascular and has serpentine signal voids of feeding vessels. However, 40% of HBs are solid. Less commonly, these tumors may be purely cystic. Overall, HB is a rare tumor representing 1-2.5 % of primary CNS neoplasms; 10-20% of all cases are associated with with von-Hippel-Lindau syndrome; converesly, 45% of patients with VHL develop HBs.

Treatment: Treatment frequently requires removal of the mural nodule only, since the cyst is not truly neoplastic. Preoperative embolization aids in resection of the highly vascular tumors. Prognosis is very good with 5-year a survival rate of more than 85%.


Radiology

Angiography: Sascular nodule with intense, prolonged stain; +/- avascular cyst
CT: Low-density cyst with strongly enhancing mural nodule that abuts a pial surface (75%)
MRI: Cyst slightly hyperintense to CSF on T1WI; hyperintense to brain on T2WI; mural nodule variable but typically enhances strongly