venerdì 31 agosto 2007
In Figure 1, an artery can be seen branching from the cavernous portion of the left internal carotid artery and joining the basilar artery. Notice the absence of this vessel on the right.
Diagnosis: Persistent Trigeminal Artery (PTA)
In the 3-5 mm human embryo, approximately 29 days after ovulation, four important arterial anastamoses join the dorsal aorta (the future internal carotid artery) to the bilateral longitudinal neural arteries (the future basilar artery). They are the trigeminal, otic, hypoglossal and proatlantal intersegmental arteries. The largest of these is the trigeminal artery. These arteries persist about a week and regress as the posterior communicating and vertebral arteries develop. For reasons that are not fully understood, these arteries sometimes fail to regress.
The most common persistent carotid-vertebrobasilar anastamotic artery is the trigeminal artery. The incidence has been reported to be about 0.2%, but if undiagnosed and unreported cases are taken into account, this number may approach 1%. There are two main classifications of a persistent trigeminal artery based on its anatomic position; lateral and medial. The lateral type leaves the cavernous sinus to course with the trigeminal root on the lateral side of the sella turcica in a groove of the posterior petrosal process and joins the basilar artery between the origin of the anterior inferior cerebellar artery and superior cerebellar artery. The medial type penetrates the sella turcica to run in its own groove and perforates the dura near the clivus to join the basilar artery.
A persistent trigeminal artery is usually an incidental finding, but has been reported to present with several clinical manifestations. Patients with a persistent trigeminal artery are at an increased risk of developing aneurysms. These aneurysms can be located either at their origin from the internal carotid artery or at their connection with the basilar artery. Depending on the artery’s anatomic location relative to the trigeminal and abducens nerves, patients can present with trigeminal neuralgia or sixth nerve palsies. Patients can present with vertigo and ataxia from embolization of a carotid atherosclerotic plaque through a persistent trigeminal artery into the posterior circulation. Patients can present with the same symptoms with a carotid occlusion which can cause a vascular steal phenomenon from the basilar artery to the carotid system through a persistent trigeminal artery. Patients with complications from a persistent trigeminal artery can be treated with endovascular or surgical interventions.
CT shows right cerebellar hemispheric hypoattenuation with edema, mass effect, and effacement of the 4th ventricle. Angiogram shows contrast blush in the right inferior cerebellar hemisphere with an early draining vein ("luxury perfusion"). Anterior and inferior displacement of the right PICA branch. No evidence of vertebral dissection or vascular malformation.
Diagnosis: Right cerebellar infarct demonstrating luxury perfusion
Luxury perfusion is a term used to describe increased circulation through an area of infarcted brain.
Thought to be due do vasodilation secondary to lowered oxygen tension and decrease tissue pH. (Loss of normal CBF autoregulation).
Angiographically seen as capillary blush and early filling of local veins.
The blush may simulate a tumor
Luxury perfusion can be seen in minutes to hours after infarction, usually resolves in 3-5 days. Never seen after 2 weeks.
mercoledì 29 agosto 2007
Repeat selected MR image
Figure 1: Initial CT of the head showed an intraparenchymal bleed in the left frontal subcortical region.
Subsequent MRI showed the bleed to be predominantly isointense on T1-WI (Figure 2) and heterogeneously bright on T2-WI (Figure 3), suggestive of hyperacute to acute stage. Mild perilesional edema is seen with no abnormal adjacent flow voids. Generalized volume loss is also noted. Gradient echo images (Figure 4 and Figure 5) show multiple, patchy areas of hemorrhage in the bilateral superficial, subcortical white matter appearing as areas of susceptibility.
Follow-up MRI shows the intraparenchymal bleed as high-signal on T1-WI (Figure 6) and hyperintense on T2-WI (Figure 7) suggestive of late-subacute nature of bleed.
Diagnosis: Cerebral amyloid disease (angiopathy)
Cerebral amyloid disease is a localized form of amyloidosis characterized by extracellular deposition of ß-amyloid in the brain, and it is not associated with systemic amyloidosis. It is found at autopsy in 33% of 60–70 year olds and the prevalence increases to 75% of people older than 90 years. Cerebral amyloid deposition occurs in three morphologic varieties, with cerebral amyloid angiopathy (CAA) being the most common with deposition of ß-amyloid protein in the media and adventitia of small and medium-sized vessels of the cerebral cortex, subcortex, and leptomeninges. Amyloidoma and diffuse encephalopathic white matter involvement are rare.
Many cases of CAA are asymptomatic. When symptomatic, typical presentations include acute intracranial hemorrhage, symptoms resembling a transient ischemic attack (TIA), or dementia. However, these symptoms are not specific for CAA and are often not readily associated with CAA. With continued aging of the population, CAA will become even more prevalent, making correct characterization of imaging findings important.
The deposition of ß-amyloid in the vessel wall is associated with fibrinoid necrosis, focal vessel wall fragmentation, and microaneurysms, which all predispose the patient to repeated episodes of blood vessel leakage or frank hemorrhage. Luminal narrowing may occur at sites of fibrinoid necrosis, which can lead to ischemic change. Histologically, ß-amyloid deposits stained with Congo red show classic yellow-green birefringence under polarized light.
Nonenhanced head CT is the preferred initial imaging modality as it provides crucial information regarding the characteristics of the intracranial hemorrhage, including size, location, shape, and extension to the extra axial spaces. MRI is best suited for identification of small or chronic cortical hemorrhages and ischemic sequalae of this disease, exclusion of other causes of acute cortical-subcortical hemorrhage, and assessment of disease progression. GRE is currently the most sensitive MR imaging sequence for detection of the chronic cortical-subcortical microhemorrhages. Local magnetic field inhomogeneity related to the presence of hemosiderin causes a marked loss of signal on T2*-weighted GRE imaging.
CAA-related ICH represents only 2% of all ICH but is an important cause of hemorrhage in normotensive elderly patients without trauma, representing 38% to 74% of ICH cases in the elderly. CAA-related ICH exhibits a distinctive cortical-subcortical distribution that generally spares the deep white matter, basal ganglia, and brainstem. Angiography does not play a role in the evaluation of CAA.
CAA should be considered in the broad differential diagnosis of leukoencephalopathy, especially if associated with cortical-subcortical hemorrhage(s) or progressive dementia. In CAA, atrophy is most likely the result of chronic small vessel ischemia related to ß-amyloid deposition and is usually seen in association with leukoencephalopathy.
There is no current treatment to halt or reverse ß-amyloid deposition. Patients with CAA have an increased risk of bleeding while taking warfarin, even when the level of anticoagulation is in the therapeutic range. The risk-benefit ratio of anticoagulation and thrombolytic therapy in CAA patients should be carefully considered on an individual basis.
venerdì 24 agosto 2007
Figure 1, Figure 2 and Figure 3: Axial T2 images exhibit reduced brainstem and cerebellar volume, and enlargement of the 4th ventricle and perimesencephalic cistern. Note the normal appearance of the supratentorial brain (Figure 3).
Figure 4 and Figure 5: Sagittal T1 images demonstrate reduced brainstem and cerebellar volume, flattening of the pons, a narrow middle cerebellar peduncle, and enlargement of the 4th ventricle.
Diagnosis: Olivopontocerebellar degeneration
Olivopontocerebellar degeneration (OPCD), once known as Dejerine-Thomas syndrome, is a neurodegenerative disorder caused by progressive infratentorial neuronal loss. The clinical presentation is variable; however, certain features predominate: parkinsonism, pyramidal dysfunction, autonomic dysfunction, and cerebellar ataxia. There is significant overlap with other neurodegenerative disorders including Shy-Drager syndrome, progressive supranuclear palsy, and striatonigral degeneration. These disorders sometimes being referred to as the “Parkinson Plus” syndromes.
Differentiation from Parkinson disease can be extremely difficult with clinical findings alone. It is also important to exclude other causes of progressive neurological decline, such as malignancy, multiple sclerosis, or cerebrovascular disease. Accurate diagnosis is crucial for purposes of patient management, prognosis, and genetic counseling.
The imaging findings of OPCD include pronounced degenerative changes throughout the brainstem and cerebellum as evidenced by flattening of the pons, reduced volume of the medullary olives and middle cerebellar peduncle, and enlargement of CSF spaces including the fourth ventricle and perimesencephalic cistern. This atrophy should be disproportionate to that found throughout the remainder of the brain. Occasionally, demyelination of the transverse pontine fibers may result in a cruciform shaped region of hyperintensity on T2WI, irreverently termed the “Hot Cross Bun” sign.
Evaluation of the middle cerebellar peduncle width is helpful in confirming the diagnosis of OPCD. A measurement of less than 8mm in the sagittal plane has been shown to be both highly sensitive and specific for the disease. Not necessary for diagnosis, but of potential academic interest- these patients will generally demonstrate reduced FDG metabolism on PET and depressed NAA/Cr ratios on MR spectroscopy in the affected areas.
mercoledì 22 agosto 2007
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.
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.
martedì 21 agosto 2007
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).
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.
venerdì 17 agosto 2007
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
- Hemolytic-uremic syndrome
Differential diagnosis (Chronic)
- Mitochondrial encephalopathies (Leigh’s disease, MELAS, Kearns-Sayre, etc.)
- 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.
mercoledì 15 agosto 2007
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).
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.
venerdì 10 agosto 2007
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.
giovedì 9 agosto 2007
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.