giovedì 27 ottobre 2005

Arteriovenous malformation


MR findings include serpiginous high and low signal (depending on flow rates) within feeding and draining vessels (Figure 1 andFigure 3). High T2 signal can be seen in the adjacent brain parenchyma secondary to gliosis, edema, or ischemia, as is seen in this case (Figure 3).
MRA reveals AVM with feeding artery branching from the left PCA. Nidus and tangled vessels are visualized (Figure 4).

Diagnosis: Arteriovenous malformation

Cerebrovascular malformations are divided into 4 major categories including arteriovenous malformation, venous angioma, capillary telangiectasia, and cavernous angioma. AVMs can be visualized with angiography, computed tomography, or magnetic resonance imaging. AVMs are the most common symptomatic vascular malformation and occur in about 0.1% of the general population. The clinical presentation is variable, including headache, seizure, and focal neurological deficits. They are occasionally discovered as an incidental finding.

AVMs are a direct communication between arterial and venous circulations and consist of a nidus of tangled dilated vessels. There are 3 subtypes that depend on the blood supply: these are pial, dural, and mixed pial-dural types. Aneurysm is associated with the feeding arteries in approximately 10% of cases. Arteriovenous shunting is usually rapid so that most vessels appear as flow voids. An AVM replaces normal brain tissue without causing mass effect, unless complicated by hemorrhage and edema. Adjacent parenchymal atrophy is common secondary to vascular steal and ischemia.

3-D TOF MRA can be diagnostically useful in demonstrating feeding arteries, the nidus, and draining veins. Occasional pitfalls in MRA evaluation include signal void in tortuous vessels, nonvisualization of draining veins resulting from spin saturation, and difficulty with differentiation of blood flow from blood clot. Conventional angiography may be necessary for treatment planning.

mercoledì 26 ottobre 2005

Thyroglossal duct cyst


Figure 1 demonstrates a cystic mass embedded in the strap muscles of the neck. Tract of thyroid tissue between cystic mass and thyroid gland is seen (Figure 2and Figure 3).

Diagnosis: Thyroglossal duct cyst

Thyroglossal duct cyst is the most common congenital neck mass and accounts for 70% of congenital neck abnormalities. Most patients present in the second decade with an enlarging, painless mass. Thyroglossal duct cysts are located in the midline (75%) or slightly off midline (25%), however, they are always within 2 cm of midline. Most cysts are located either at (15%) or below (65%) the level of the hyoid bone. On CT, the cysts usually appear as a smooth, well-circumscribed mass with a thin wall and homogeneous attenuation, measuring fluid in attenuation. Elevated attenuation levels may reflect increased protein content and can correlate with history of prior infection. Peripheral rim enhancement is usually observed on contrast-enhanced scans.

Thyroid gland development begins in the third week of fetal life as a median outgrowth from the primitive pharynx at the level of the foramen cecum, which lies at the junction of the anterior two thirds and posterior one third of the tongue. The primitive thyroid descends in the neck and passes anterior to the hyoid bone and laryngeal cartilages. The gland reaches its final position in the inferior part of the neck by the seventh week after descending anterior to the thyrohyoid membrane and strap muscles. During the migration, the analage of the thyroid gland is connected to the tongue by a narrow tubular structure, the thyroglossal duct. This structure usually involutes by the eighth to tenth week of gestation. If any portion of the duct persists, secretions from the epithelial lining may give rise to cystic lesions.

The differential diagnosis includes obstructed laryngoceles and branchial cleft cysts. Laryngoceles are dilated laryngeal saccules. They may appear as a well-defined smooth mass in the lateral aspect of the superior paralaryngeal space. They may occur deep to the strap muscles, however, they arise within the larynx and can be visualized to connect back to the larynx. Failure of complete obliteration of an embryonic branchial cleft in the eighth to ninth week of fetal development results in a branchial cleft cyst, 95% of which derive from the second branchial cleft. Branchial cleft cysts usually manifest in the young adult as a mass near the mandibular angle (submandibular space), however, they can occur anywhere along the residual cleft tract extending from the suprclavicular region to the tonsillar fossa. Typically, the cyst is a round or oval mass that displaces the sternocleidomastoid muscle posteriorly or posterolaterally, the carotid artery and internal jugular vein medially or posteromedially, and the submandibular gland anteriorly.

mercoledì 19 ottobre 2005

Colloid cyst


There is a hyperdense cyst at the roof of the third ventricle at the foramen of Monro (Figure 1, Figure 2, Figure 3 andFigure 4). There is no enhancement of the cyst. The ventricles are nondilated.

Diagnosis: Colloid cyst

Colloid cysts are rare cystic lesions that are classically located at the anterior roof of the third ventricle at the foramen of Monro. They can be pedunculated, which can make the cyst mobile and lead to sudden ventricular obstruction at the foramen of Monro. Patients are typically in their third to fourth decade of life and present with intermittent or persistent headaches due to the increased intracranial pressure from obstruction of CSF outflow. Colloid cysts are treated microsurgically, endoscopically, or with biventricular shunts in nonsurgical candidates. These are surgical emergencies in cases of acute hydrocephalus.

Colloid cysts are typically hyperdense on noncontrast CT and typically do not demonstrate any enhancement. Case reports have documented rare cyst wall enhancement. Their MR characteristics are variable due to the variations in protein, mucin, and water content of the cyst fluid. Calcifications and hemorrhage are rare.