giovedì 31 maggio 2007
Axial T1 and T2 (Figure 1 and Figure 2) demonstrate a mass with intermediate T1-weighted signal and intermediate-to-high T2-weighted signal.
Axial T1 postcontrast (Figure 3) demonstrates avidly enhancing mass in right maxillary sinus that widens the sphenopalatine foramen.
Figure 4 (coronal) contrast enhanced T1-weighted images demonstrate flow voids within the enhancing mass. Flow voids are characteristic of a juvenile angiofibroma.
Flow voids are seen as dark areas on T2-weighted image (Figure 2) as well.
Diagnosis: Juvenile angiofibroma
Juvenile angiofibroma (JAF) presents in adolescent males (median age 15) with unilateral nasal obstruction and epistaxis. JAF is rare, representing 0.5 % all head and neck neoplasms; however, it is the most common benign neoplasm of the nasopharynx. Although the commonly used synonym is juvenile nasopharyngeal angiofibroma, true JAF entity arises in the nasal cavity, not the nasopharynx. However, it may spread into the nasopharyx.
JAF is considered benign but locally aggressive. Approximately 20 % have skull base invasion at diagnosis.
On imaging, JAF is a highly enhancing mass that is lobulated and nonencapsulated. Microscopically, it is composed of delicate thin-walled vessels on a background of connective tissue stroma. These delicate vessels lend the mass its tendency to bleed easily.
JAF originates at the posterior nasal cavity along the superior margin of the sphenopalatine foramen and posterior aspect of middle turbinate As it enlarges, this mass may fill the unilateral nasal cavity, and extend into the nasopharynx and pterygopalatine fossa (90%). If there is superior extension, it will involve the sphenoid sinus (60%). When it pushes anteriorly against the posterior wall of the maxillary sinus, it results in the classic “antral bowing sign” on CT examination. A small number may actually invade into the middle cranial fossa via the foramen rotundum or vidian canal. In these cases, bony destruction is evident.
On MRI, there is T1 intermediate signal and T2 intermediate-to-high signal. Flow voids are often seen in these very vascular tumors. Biopsy of this lesion is considered unnecessary and dangerous, given its propensity to bleed. An angiogram of both ECA and ICA with embolization using polyvinyl alcohol particles or Gelfoam is often performed 1-2 days before surgery to reduce surgical blood loss and decrease rate of recurrence. Local recurrence after surgery is 6-24%. Low dose radiation may be used in conjunction with surgery for cure. Rarely, chemotherapy has been utilized in cases of intracranial extension with favorable results.
Several staging systems have been described to help predict outcome. Chandler et al (1984) described the following:
- I) Tumor confined to nasopharyngeal vault.
- II) Tumor extends into nasal cavity or sphenoid sinus
- III) Tumor extends into antrum, ethmoid sinus, pterygomaxillary fissure, orbit, and/or cheek
- IV) Intracranial tumor
venerdì 25 maggio 2007
Additional clinical data: The patient has a history of hypocalcemia.
Diffuse, symmetric calcification of the deep gray matter and bilateral immediate subcortical white matter (U-fibers). No acute intracranial hemorrhage or abnormal extra-axial fluid collections. No focal mass, mass effect, or shift of midline structures. Stable, normal ventricle sizes and configuration.
- Fahr's disease
- Post-infectious (e.g. toxoplasmosis)
- Post-radiation therapy
Pseudohypoparathyroidism (PHP) is a congenital hereditary abnormality that appears to be transmitted as an X-linked dominant trait characterized by hypocalcemia, hyperphosphatemia, and basal ganglia / soft tissue calcification. In PHP, biochemical hypoparathyroidism results from end-organ resistance to parathyroid hormone, due to a defect in the receptor-adenylate cyclase system. As a result, the kidney and, less commonly, the bones are unable to respond to parathyroid hormone.
Afflicted patients may be short-statured with rounded faces. Brain calcinosis may be seen in conditions with PHP, the severity and distribution of which varies in individual reports. Bilateral calcifications may present in the basal ganglia, thalamus, cerebral white matter, and cerebellum on head CT. The intracranial calcifications of the basal ganglia may later coalesce into homogeneous masses. Osteosclerosis, which may be generalized or localized, is the most common skeletal abnormality, including calvarial thickening. Subcutaneous calcifications can be seen, especially in the area of the hips and shoulders.
giovedì 24 maggio 2007
Axial images show a heterogeneous mass in the anterior left temporal lobe. T1-weighted images show hyperintense regions suggesting fat involving the left parietal and temporal lobe leptomeninges suggesting fat and/or blood products. These same areas show patchy foci of hypointense signal on fat-suppressed T2. Postcontrast axial images do not show enhancement of the left temporal mass.
- Dermoid cyst
- Metastatic lesion
Diagnosis: Dermoid cyst
Dermoid cysts are comprised of connective tissue, squamous epithelium, lipid, and glandular tissue. They sometimes also include calcifications.
Congenital lesions, which are usually midline. Most commonly in the posterior fossa or suprasellar region. Can be seen in the spine, often involving the conus medullaris and cauda equina.
Benign and slow-growing due to glandular secretions and accumulation of epithelial debris. Symptoms are secondary to mass effect.
Dermoid cysts can rupture and release lipid contents into the subarachnoid spaces, which can cause chemical meningitis. Most common symptom postrupture is headache. Meningeal inflammation can (but rarely does) lead to arterial vasospasm and stroke or death.
No role for chemotherapy or radiation therapy in treating dermoid cysts. Resection must include the contents and entire connective tissue lining. Special care must be taken not to spill contents or meningitis will ensue.
On CT, hypodensity suggesting significant fat composition suggests the diagnosis.
On MR, a heterogeneous often midline mass showing hyperintense regions on T1-weighted images may represent a dermoid cyst. Diffuse subarachnoid or intraventricular foci of hyperintensity on T1-weighted imaging that lose signal on fat-suppressed images are concerning for rupture and subsequent chemical meningitis.
mercoledì 23 maggio 2007
Axial T1-WI (Figure 1) demonstrates a well-defined, cortical based intraxial mass in the right temporal lobe which is hypointense to brain parenchyma. The mass is hyperintense on T2-WI (Figure 2). No surrounding edema is seen. The right temporal horn is seen normally. No enhancement is detected on post-gadolinium T1-WI (Figure 3). Scalloping of the adjacent skull is noted with the lesion “pointing” towards the ventricle (Figure 3).
Diagnosis: Dysembryoplastic Neuroepithelial Tumor (DNET)
DNET is an uncommon benign intracortical lesion that is classified by WHO as a “neuronal and mixed neuronoglial tumor”. These are commonly associated with cortical dysplasia. DNETs show no or very slow growth over time and are WHO Grade I.
These tumors virtually always manifest in patients with medically refractory partial seizures. The vast majority of patients are younger than 20 years, and males are more commonly affected. The temporal lobe is the most common site (62%), followed by the frontal lobe (31%).
The imaging appearance of dysembryoplastic neuroepithelial tumor is similar to those of other low-grade glial tumors. On CT, a wedge shaped low-density area is seen in a cortical/ subcortical location “pointing” towards the ventricle. Calcification may be seen in 25% of cases. Scalloping of the adjacent inner table of the skull suggests long standing nature of the lesion.
At MR imaging, DNET tumors most commonly manifest as cortical masses that are hypointense on T1-weighted images and hyperintense on T2-weighted images without surrounding vasogenic edema. Pseudocystic, multinodular “bubbly” mass may be seen. DNETs usually do not enhance- faint focal punctuate or nodular enhancement may be seen in 20% cases.
The prognosis is excellent with long survival even with incomplete tumor resection. Most patients have a significant reduction in seizure frequency. Tumor recurrence is very rare.
venerdì 18 maggio 2007
NECT images show low density in the bilateral globus pallidi. The remainder of the basal ganglia and hemispheric white matter is unremarkable.
- Carbon monoxide poisoning
- Acute hypoxia of other causes
- Small vessel ischemic disease
- Creutzfeldt-Jakob disease (and other encephalidites)
- Wilson’s disease (and other metabolic processes)
Diagnosis: Carbon monoxide poisoning
Bilateral GP low density on NECT is virtually pathognomonic of CO poisoning.
MRI is more accurate and should be used for follow-up.
Normal CT on arrival correlates with better prognosis.
Carbon monoxide poisoning remains an important cause of morbidity/mortality in the US despite improvements in automobile and home safety. While nearly 50% are due to suicide and many are associated with fires, a large number of unintentional CO poisonings still occur. Race and source of CO are also important, as CO poisoning in Caucasians is more likely to be suicidal and fatal than in African- or Asian-Americans. Also, toxicity from automobile exhaust is more likely to be fatal, and malfunctioning heating equipment is a more common source.
Patient clinical history may include unresponsiveness, seizure, or adjunctive information such as multiple patients from the same household. Nausea, vomiting and headache are more general symptoms which are often associated with a lower degree of toxicity.
For most patients the initial imaging study is a NECT following ER evaluation. Hypodensity in the bilateral GP is a strong indicator for this process and is virtually pathognomonic. CT findings are also indicative of outcome. A patient with a normal head CT is very unlikely to have long-term neurological abnormalities.
MRI is much more accurate than CT in defining the extent of disease (e.g. white matter ischemic changes, internal capsule or caudate nucleus involvement). As such, this is the preferred modality for follow-up. Findings include T1 hypointensity (necrosis) or hyperintensity (hemorrhage), T2 and FLAIR hyperintensity, hypointense rim on T2 (hemosiderin deposition), and DWI hyperintensity in the acute setting.
mercoledì 16 maggio 2007
Figure 1: Sagittal T1 demonstrates midline cystic structure in the posterior pharynx which demonstrates increased signal intensity on T1WI.
Figure 2 and Figure 3: Axial T1 and T2 demonstrate the lesion with variable signal intensity based on protein content. When increased protein content is present, T2WI is decreased as in Figure 3. The lesion is anterior and adjacent to the superior pharyngeal constrictors.
Diagnosis: Tornwaldt cyst
Described by Gustav Ludwig Tornwaldt (1843-1910), a Tornwaldt cyst, or bursa pharingea, is a benign developmental cyst which is found in posterior nasopharyngeal soft tissues, anterior to the superior pharyngeal constrictors. The lesion is nearly always midline, although off-midline is possible. Identified in about 3% of patients, this cyst has no sex predilection with a peak incidence in patients from 15-30 years of age.
The cyst is formed during development, from a diverticulum which results from an adhesion between the notocord and endoderm of the posterior pharynx. As the notocord retracts normally into the clivus and cervical spinal column, a midline nasopharyngeal epithelial lined outpouching may close, forming a cyst. This is a part of the pharyngeal roof and a remanant of the Rathke’s pouch. Some authors believe that the lesion arises from a remnant of the notochord itself.
On CT, Tornwaldt cyst appears as a hypodense lesion in the midline in nasopharyngeal soft tissues. On MRI they demonstrate variable intensity depending on the degree of proteinaceous content, however are typically hyperintense on T1, T2 as well as FLAIR sequence images. The size of the lesion can vary from 5mm to a few centimeters.
These cysts are nearly always asymptomatic. They infrequently become infected resulting in neck pain or muscle spasm. If the cyst ruptures due to infection or trauma, the release of anaerobic contents may result in halitosis, eustachian tube obstruction or possibly an upper respiratory tract infection.
When symptomatic, treatment option includes surgical excision or marsupialization.
lunedì 14 maggio 2007
3-D CT images demonstrate sagittal synostosis. Markedly increased anteroposterior diameter of the head (dolichocephaly) with flattening of the superior contour is noted. The sagittal suture is fused (Figure 1 and Figure 2), with widening of both the coronal (Figure 2) and lambdoid sutures (Figure 1 and Figure 2).
Diagnosis: Sagittal synostosis
Premature fusion of the cranial sutures is termed craniosynostosis. Approximately 80-90% cases involve isolated defects, while the remaining cases are part of a recognized syndrome. In the isolated cases, the sagittal suture is affected most often (55%), followed by the coronal (20%), lambdoid (5%), and metopic (5%) sutures. Syndromes associated with synostosis include Crouzon disease and Chotzen and Apert syndromes.
The anterior fontanel represents the intersection of the metopic, coronal, and sagittal sutures. It normally closes in children by the age of 20 months. The posterior fontanel, located at the junction of the lambdoid and sagittal sutures, closes by the age of 3 months. Skull growth is restricted in the plane perpendicular to the prematurely fused suture and enhanced in the plane parallel to it.
Sagittal synostosis produces a long and narrow skull, called scaphocephaly or dolichocephaly. The AP diameter of the skull is increased, whereas the transverse diameter is decreased. Actual head volume is normal and there is no increase in ICP, no hydrocephalus, and no neurologic deficit.
Coronal synostosis can occur bilaterally or unilaterally and is called brachycephaly and plagiocephaly (twisted and asymmetric skull), respectively. Brachycephaly results in a short, wide skull, with a shortened AP diameter with a flattened occiput and forehead. It has a higher incidence of neurologic complications, including increased ICP, optic atrophy, and mental retardation.
Lamboid synostosis produces a marked flattening and underdevelopment of the posterior fossa and overgrowth of the bregma may occur, resulting in a tall tower like shape called oxycephalic or turricephalic skull.
Metopic synostosis occurs in utero. It is rare, and results in a pointed forehead and hypotelorism called trigonocephaly, and has an increased risk for associated anomalies of the forebrain.
The most severe form is called the kleeblattschädel deformity or cloverleaf skull, in which the coronal, sagittal, and lambdoid sutures are all affected. The skull resembles a cloverleaf shape, and patients typically have a bulging forehead, proptotic eyes, and severe neurologic impairment.
The signs of craniosynostosis on plain radiography include bony bridging across the suture that produces beaking or heaping up of bone as well as sclerosis, straightening and narrowing of the suture.
The diagnostic value of the CT scan outweighs that of plain radiography because the sutures can be identified more accurately. In addition, CT helps in evaluating the brain for structural abnormalities (eg, hydrocephalus, agenesis of the corpus callosum) and in excluding other causes of asymmetric vault growth (eg, brain hemiatrophy, chronic subdural hematoma). Three-dimensional surface CT reconstructions can help the surgeon to accurately delineate the craniofacial deformity and plan surgical management.
giovedì 10 maggio 2007
Figure 1, Figure 2, and Figure 3: T2, DWI, and ADC map show increased signal and restricted diffusion in the basal ganglia. More specifically there is symmetrically increased signal in the caudate and putamen with sparing of the globus pallidus. Additional areas of increased signal are seen in the right and left parietal cortex (Figure 4). No contrast enhancement was seen.
Diagnosis: Creutzfeldt-Jakob Disease - Sporadic form
CJD is a progressive fatal neurodegenerative disorder caused by prion proteins accumulating within the neurons.
There are three forms of CJD. A familial form, a sporadic form, and a variant or iatrogenic. form. The sporadic form (sCJD) is identified in 85% of cases. No genetic or infectious cause can be identified in these patients.
The familial or genetic form (fCJD) is seen in 15% of cases. These cases are identified by DNA analysis of the PRPC gene mutations.
Though it receives the most media attention, the infectious variant or iatrogenic form (vCJD) is the rarest, accounting for 1% of cases.
Diagnosis is based on clinical presentation, EEG findings, and a positive CSF analysis showing 14-3-3 proteins. MRI is reported to have high sensitivity and specificity for the disease with characteristic symmetric signal abnormalities in the basal ganglia and cortical abnormalities. The caudate and putamen are the most frequently involved nuclei. Thalamic involvement is only seen in 14% of patients with the sporadic form. However, thalamic involvement is seen in 78-100% of the variant/iatrogenic forms of CJD. The globus pallidus is usually spared. Diffusion weighted sequences are the most sensitive. Abnormalities are also well seen on T2 and FLAIR weighted sequences. The basal ganglia and cortical lesions show increased signal on T2 and FLAIR with persistent restricted diffusion. The cause of the restricted diffusion is not completely understood.
No treatment is available for the disorder at this time. The clinical course is usually progressive and rapid with most patients expiring within six months to one year from the time of diagnosis.
lunedì 7 maggio 2007
Marked thickening of the skull base with narrowing of all the neural foramina. Hydrocephalus.
- Craniometaphyseal dysplasia
- Frontometaphyseal dysplasia
- Craniodiaphyseal dysplasia
Diagnosis: Craniometaphyseal dysplasia
Craniometaphyseal dysplasia is a rare genetic disorder whereby stromal cells are not able to differentiate osteoclast precursors, resulting in craniofacial and long bone abnormalities and cranial nerve palsies.
Autosomal dominant form has variable expression. Autosomal recessive is more severe.
Radiologic findings include hyperostosis of the skull base, narrowing of the neural foramina which exit the skull base, and fraying or "celery stalking" of the metaphyses, usually in the lower extremities.
These children have normal growth, normal intelligence, no bone fragility and no growth retardation.
In this particular case:
- This patient has had bilateral cranial nerve VII decompression secondary to bony overgrowth of the neural pathway. This patient also has optic canals which are 50% smaller than normal
- This patient developed new hydrocephalus due to stenosis of the jugular foramina. The resultant venous hypertension created hydrocephalus by disturbing the pressure gradient which is necessary for CSF drainage into the venous system
Other dysplasias similarly affecting parts of the skull:
- Craniodiaphyseal dysplasia: children have mental retardation, massive sclerosis of the skull, retarded growth
- Frontometaphyseal dysplasia: X linked, hyperostosis of the skull base and vertex, mandibular hypoplasia, sinus obliteration
venerdì 4 maggio 2007
Figure 1: T2-weighted axial image demonstrates a heterogeneous, intraventricular mass with cystic regions.
Figure 2 and 3: Axial FLAIR images demonstrates an intraventricular mass abutting the septum pellucidum with increased FLAIR signal.
Figure 4, Figure 5, Figure 6, and Figure 7: Postcontrast T1-weighted images demonstrate a heterogeneously enhancing lesion that abuts the septum pellucidum.
- Central (intraventricular) neurocytoma
- Subependymal Giant Cell Astrocytoma (SGCA)
- Choroid plexus papilloma
Diagnosis: Central (intraventricular) neurocytoma
Although central neurocytomas account for less than 1% of all intracranial neoplasms, they constitute approximately 50% of intraventricular tumors in patients 20-40 years old. Most present with headache, signs and symptoms of increased intracranial pressure, seizure, or change in mental status. In rare cases tumors with neurocytoma features may involve the brain parenchyma or spinal cord and are referred to as extraventricular central neurocytomas. These have a worse prognosis.
There is controversy regarding whether the embryological origin of central neurocytomas arises from neuronal or bipotential progenitor cells. They have a more benign appearance with uniform round cells with neuronal differentiation. Anaplastic features and necrosis is rare. Histologically, central neurocytomas are difficult to distinguish from oliogodendrogliomas, and immunohistochemical staining for synaptophysin and neuron specific enolase (positive in neurocytoma) is used to differentiate the two. They are considered as WHO grade II astrocytomas.
CT demonstrates a mixed solid and cystic lesion within the lateral ventricle with moderate, heterogeneous enhancement. Most lesions occur in the body or frontal horns of the lateral ventricle or near the foramen of Monro. This can result in obstructive hydrocephalus. Calcification occurs in 50-70% of cases. On MR the lesion is heterogeneous with the majority of the lesions being isointense to gray matter on T1 and the cystic regions being hypointense on T1 and hyperintense on T2. Prominent flow voids can also be seen. On FLAIR sequences the mass is heterogeneous and predominantly hyperintense. Contrast enhanced MR is the preferred imaging modality in these cases. MR spectroscopy demonstrates a large choline peak. Central neurocytomas typically demonstrate decreased activity on PET imaging.
Most central neurocytomas are treated with complete surgical resection, which is usually curative. These tumors are typically benign and rarely invade brain parenchyma or develop local recurrence. In cases of local recurrence or incomplete resection radiation therapy, chemotherapy, and/or radiosurgery can be employed as adjunct treatments. Overall the 5 year survival rate is over 80%.
martedì 1 maggio 2007
Broad based extra-axial mass located in the left cerebellar pontine angle extending to the porous acousticus but not entering the internal auditory canal. The mass demonstrates isointensity relative to gray matter on T1-weighted and mildly increased signal on T2-weighted sequences. The mass enhances homogeneously with contrast. There is moderate mass effect on the brachium pontes.
Differential diagnosis for a cerebellar pontine angle (CPA) mass:
- Arachnoid cyst
Diagnosis: Cerebellar pontine angle meningioma
CPA meningiomas are often positioned eccentric to the porous acousticus
CT findings: NECT
- 70% hyperdense, 30% isodense; 25% calcified
- Hyperostosis or permeative bone changes
- IAC flaring
+ CECT: 90% strong uniform enhancement, 10% inhomogeneous
MRI findings (See table below)
- Dural vessels supply tumor center and pial vessels supply the rim
- Sunburst pattern of enlarged dural feeders
- Vascular stain in venous phase
- Arteriovenous shunting may be present