giovedì 27 agosto 2009
Initial head CT without contrast: Subarachnoid hemorrhage seen filling the quadrigeminal cistern, suprasellar cistern, and surrounding sulci. This is most prominent in the posterior fossa. There is associated intraventricular hemorrhage and moderate obstructive hydrocephalus. CT head angiography: There is a 3mm L superior cerebellar artery aneurysm
Diagnosis: Subarachnoid hemorrhage secondary to rupture of left superior cerebellar artery aneurysm.
The most common presenting symptom of SAH is "the worst headache of my life." The peak incidence is around 40-60 years of age and is slightly more common in females. Subarachnoid hemorrhage localized to the posterior fossa is uncommon in the setting of trauma and suggests posterior circulation aneurysmal rupture. Hemorrhage is most extensive at the site of aneurysm. Most common sites of aneurysm are in order of decreasing frequency: Anterior communicating artery, posterior communicating artery, middle cerebral artery, anterior cerebral artery, basilar artery, internal carotid artery, PICA, vertebral artery, and superior cerebellar artery. Saccular, berry, or congenital aneurysms constitute 90% of all cerebral aneurysms and are located at the major branch points of large arteries. Infectious or mycotic aneurysms are situated peripherally and comprise 0.5% of all cerebral aneurysms. Amyloid angiopathy typically produces more peripheral areas of hemorrhage.
Staging, grading or classification criteria
- Grade 1: Thin SAH = 5 mm
- Grade 2: Thick SAH > 5 mm
- Grade 3: Thin SAH with mass lesion(s)
- Grade 4: Thick SAH with mass lesion(s)
Lower grades have better admission Glasgow coma scores & discharge Glasgow outcome scale scores.
50% mortality, 15% rebleed within first 24 hr
Natural history: Breakdown & resorption from CSF
Complications: Acute hydrocephalus, delayed hydrocephalus, vasospasm
- Rare; usually obstruction of aqueduct or 4th ventricular outlet by clotted SAH
bstructive, non-communicating hydrocephalus
- Asymmetric ventricular dilatation
- Arachnoid granulation defect in CSF resorption
- Obstructive communicating hydrocephalus
+ Symmetric ventricular dilatation
- May develop quickly (2-3 days post-injury)
- Peaks 7-10 days post-injury, threat remains up to 2 weeks
- Uncommon cause of post-traumatic infarct
Best diagnostic clue: Hyperdense CSF on non-contrast CT
Suprasellar, basal, Sylvian & interhemispheric cisterns most common location
Hemorrhage most extensive at site of aneurysm
CT without contrast: 95% positive in first 24 hr, < 50% by 1 week
CTA 90-95% positive if aneurysm = 2 mm
FLAIR: Hyper intense; FLAIR more sensitive than CT but less specific
MRA: 85-95% sensitive: Insufficient detail for surgery
Difficult to see on T1WI, T2WI & GRE
T1WI: CSF mildly hyper intense ("dirty")
Angiography: Negative in 15% of aSAH; repeat positive < 5%
Figure 1 (unenhanced CT): Well-circumscribed, noncalcified, hyperdense mass in the suprasellar cystern (arrow).
Figure 2 (MRI T1 w/o contrast): Sellar/suprasellar mass, isointense to white matter, with mass effect on the undersurface of the optic chiasm, without hydrocephalus.
Figure 3 (Coronal T1 w/contrast): Mass demonstrates homogenous enhancement.
Figure 4 (Sagittal T1 w/contrast): Extension of mass along a thickened pituitary stalk into the hypothalamus.
Diagnosis: Granulomatous hypophysitis
Granulomatous hypophysitis is a rare inflammatory process, accounting for approximately 1% of pituitary lesions. This entity may be mistaken for a pituitary neoplasm, such as an adenoma. Unlike lymphocytic hypophysitis, which predominantly affects females, young women in late pregnancy or postpartum period, granulomatous hypophysitis appears to have no gender predilection and average age at diagnosis is greater than 40 years.
Patients often present with a headache. Other symptoms may include hypopituitarism, diabetes insipidus, hyperprolactinemia, or symptoms associated with chiasmal compression. While preoperative diagnosis is desirable, diagnosis is most often made postoperatively. Granulomatous hypophysitis may be idiopathic or associated with systemic granulomatous disease, such as tuberculosis, syphilis, sarcoidosis, Crohn’s disease or Wegener’s granulomatosis. It also may be associated with foreign body reactions, such as a ruptured Rathke’s cleft cyst or mucocoele.
Imaging characteristics demonstrate a sellar mass with a tongue-like suprasellar extension. The lesion may contact or infiltrate the basal hypothalamus. Pituitary stalk thickening is often a prominent feature. The lesion usually shows marked, homogenous enhancement, although heterogeneous and ring-like enhancement also occur.
martedì 18 agosto 2009
Initial noncontrast Head CT obtained 4 hours after symptom onset shows hyperdense middle cerebral artery sign (left image) in the proximal right middle cerebral artery. There is subtle loss of differentiation between cortical gray matter and subjacent white matter in the right MCA distribution, including the insular cortex (insular ribbon sign).
CT Angiography obtained 2 days after the onset of symptoms confirms an absence of blood flow distal to the right MCA M1 segment occlusion (right image below). Opacification of distal MCA branches is seen through pial collaterals.
Repeat CT Head 6 days after the onset of symptoms (right image) demonstrates continued evolution of large right MCA ischemic infarction, with a large area of hypodensity with loss of gray-white matter differentiation and effacement of cortical sulci in the right MCA distribution.
Diagnosis: Acute right MCA ischemic infarction
Causes of ischemic stroke:
- Cardiac emboli
- Amyloid angiopathy
- Hypercoagulable state
- Venous thrombosis
- Arterial dissection
- Drug abuse
Differential diagnosis for clinical presentation of acute ischemic stroke:
- Subdural hematoma
- Intracerebral hemorrhage
- Hemiplegic/hemisensory migraine
- Transient ischemic attack
Stroke is the 3rd leading cause of death in the United States, with the mortality rate from each episode estimated between 15%-35%.
The middle cerebral artery is the most common major vessel involved, with 75% of ischemic infarctions arising in the MCA territory.
Pathophysiology: Ischemia from vascular occlusion or hypoperfusion leads to cascade of cellular events resulting in failure of membrane pumps, causing efflux of potassium ions and influx of calcium ions, sodium ions, and water. This leads to cytotoxic edema, which can be detected on imaging studies as increased water content in the affected area.
The imaging characteristics of cerebral infarction are caused primarily by changes in brain water. This causes hypoattenuation on CT, low signal on T1-weighted MR images, and high signal on T2-weighted and diffusion-weighted MRI.
Noncontrast CT represents an important branching point in the work-up of suspected stroke. Its chief utility is detecting the presence or absence of hemorrhage, which contraindicates thrombolytic therapy.
Abnormalities on non-contrast CT can be seen between 3 and 6 hours after vessel occlusion in 60% of patients. The sensitivity for detecting ischemic stroke improves markedly by 24 hours after the event.
Early signs of ischemic MCA infarction on CT:
- Hyperdense middle cerebral artery sign: The actual thrombus can be visualized as a hyperdense focus within the vessel in 35-50% of acute MCA occlusions.
- Insular ribbon sign: Loss of gray-white differentiation in the insular cortex.
- Lentiform nucleus edema sign: Hypoattenuation from early edema in the putamen.
- Subtle effacement of cortical sulci (only 8% in early acute phase).
- Calcification within a vessel wall or high hematocrit level in normal arteries can mimic the hyperdense vessel sign.
- Hemorrhagic transformation occurs in 15% of MCA infarcts.
mercoledì 12 agosto 2009
Axial non contrast enhanced CT shows a large lesion isointense to the brain in the frontal lobes crossing the midline.
Contrast enhanced axial image shows avid contrast enhancement of the lesion.
T2W axial image shows a mixed signal large lesion with little surrounding edema.
Proton density axial image shows a lesion which is largely isointense to the surrounding brain parenchyma.
The lesion is low signal on TIW image with marked contrast enhancement.
Post contrast TIW sagittal image shows the lesion to be extra axial with contrast enhancement.
Diagnosis: Olfactory Meningioma
Meningiomas are the most common extraaxial tumor. The features which suggest an extraaxial etiology are tumor relationship to the dura, local bony hyperostosis, corticomedullary buckling, displacement of the cortex away form the bone, preservation of the grey/white matter junction and widening of the cisterns. Meningiomas are located in a supratentorial location in about 90% of cases, most commonly at the convexity of the hemispheres. Meningiomas are more common in females.
On unenhanced CT, meningiomas are mostly hyperdense with intense homogenous uniform enhancement. They may be associated with hyperostosis of the adjacent bone. In most cases the surrounding edema is minimal, another feature which distinguishes it from an intraaxial lesion. The dural tail sign is a non-specific sign but one that suggests a meningioma. On MR, meningiomas are isointense to hypointense on TIW images with marked contrast enhancement. On T2W images they are isointense to slightly hyperintense in signal.
The multiplanar imaging capability of MR is useful in defining the exact anatomical location of the lesion.
The olfactory groove meningioma accounts for about 10% of intracranial meningiomas. They arise in the midline between the crista galli and tuberculum sella. Olfactory groove meningiomas may be symmetrical around the midline or extend to one side or the other. 10 to 15% grow into the ethmoid sinuses. They may present with anosmia, personality change, psychological effects, epilepsy and other frontal lobe symptoms. When large they may involve the visual pathways causing visual field defects. They are slow growing tumors frequently reaching large size before detection.
venerdì 7 agosto 2009
A sagittal T2 weighted MR of the thoracic spine demonstrates a fluid collection in the ventral epidural space from T2-T3 to T7-T8. This collection is iso-to hyperintense on T1 weighted sequences, and hypointense on T2 weighted sequences, consistent with recent hemorrhage.
A post contrast axial image through the upper chest demonstrates high attenuation within the ventral epidural space at the T6 level which is not visualized on the corresponding pre contrast images, consistent with active extravasation of contrast.
Diagnosis: Spontaneous Spinal Epidural Hematoma with Evidence of Active Extravasation
Spontaneous epidural hematomas of the spine are uncommon, with a reported incidence of 0.1 per 100,000 per year. In regards to location in adults, they occur most frequently in the thoracic followed by lumbar, followed by cervical spine and are usually dorsally located. The source of bleeding is most often venous and may occur with only minimal trauma or with transient venous hypertension from Valsalva maneuvers such as sneezing or coughing. Coagulopathy, vascular anomalies, disc herniations, pregnancy, and Paget's disease are all possible underlying etiologies. However as in this case, 40-50% of cases are idiopathic.
Patients typically present with acute onset of neck, back, or radicular pain, often mimicking acute disc herniation. Obviously the size of the epidural hematoma dictates the severity of neurologic symptoms and urgency of intervention. Men are affected 4 times more frequently than women, and the entity demonstrates a bimodal distribution most commonly occurring in children and patients in their 50's and 60's.
Noncontrast CT may demonstrate a hyperdense epidural mass however when an epidural hematoma is suspected, MR is the imaging modality of choice. Signal charcateristics will vary depending on the age of the hemorrhage. Fat suppressed images may be helpful to differentiate from fat. On MR or CT post-contrast images, focal or central enhancement in the region may demonstrate active extravasation of contrast, as in this case. Peripheral enhancement has been described frequently, and may be secondary to the localized inflammation of the dura. Other important etiologies to consider in the differential diagnosis include disc extrusion/migration, epidural mets, lymphoma, epidural abscess, epidural lipomatosis, or subdural hematoma. Obviously history and onset of symptoms may help to differentiate. As mentioned, disc extrusion/migration may be associated with a spontaneous spinal epidural hematoma.
Treatment of this entity is highly variable, depending on the severity of symptoms. Overall mortality is around 5%. Extreme cases may require immediate evacuation and decompression laminectomy. If the patient has a coagulopathy, correction is usually required. Steroids may be helpful to decrease inflammation and cord edema. Many times however, conservative management is appropriate and the hemorrhage often resolves spontaneously, as demonstrated in this case.
giovedì 6 agosto 2009
Axial CT images of the head in brain parenchyma and bone windows demonstrate the characteristic findings of DDMS. The right cerebral hemisphere is atrophic. The right lateral ventricle and cortical sulci are enlarged. The right calvarium is thickened with hypoplasia of the right anterior and middle cranial fossae. The right frontal sinus is hyperpneumatized. The falx attachment is displaced to the right.
Coronal CT image in brain parenchyma window demonstrates elevation of the petrous ridge, sphenoid wing and orbital roof.
Frontal scout image demonstrates calvarial asymmetry. The right calvarium is thickened with elevation of the sphenoid wing and orbital roof.
Differential diagnosis (unilateral cerebral atrophy with ipsilateral calvarial hypertrophy)
- Dyke-Davidoff-Masson syndrome
- Rasmussen Encephalitis
- Sturge Weber syndrome
Diagnosis: Dyke-Davidoff-Masson Syndrome (DDMS)
In 1933 Dyke, Davidoff and Masson described a condition of developmental asymmetry characterized by facial asymmetry, seizures, contralateral hemiplegia, learning difficulties and cranial asymmetry on skull radiographs. Today CT and MRI are available to further delineate the bone and parenchymal changes of the Dyke-Davidoff-Masson syndrome (DDMS).
The primary process in DDMS is asymmetric cerebral hemisphere growth with atrophy of one side. The ipsilateral lateral ventricle and cortical sulci enlarge as a result of parenchymal volume loss. Compensatory osseous thickening is an adaptive response to the unilateral decrease of brain substance and results in ipsilateral calvarial thickening, overdevelopment of the paranasal sinuses and mastoid air cells, elevation of the petrous ridge, sphenoid wing and orbital roof and hypoplasia of the middle and anterior cranial fossae. Ipsilateral displacement of the falx attachment is a key finding of DDMS. Importantly, this distinguishes the concomitant ipsilateral midline shift as a developmental anomaly.
DDMS can result from cerebral injury in utero or early in life. In the prenatal period causes include congenital malformation, infection and vascular insufficiency. In the perinatal and postnatal periods, causes include trauma, anoxia, intracranial haemorrhage, tumour, infection and prolonged seizures. The involved cerebral hemisphere will have enlarged sulci if the cerebral injury occurred after birth or after completion of sulcation. In contrast, if the cerebral injury occurred during embryogenesis no prominent sulci will be present.
Rasmussen encephalitis is a chronic, progressive, immune mediated disorder thought to be secondary to viral infection. It usually presents with intractable epilepsy which progresses to continuous focal seizures, hemiplegia and cognitive deterioration. The imaging features include increasingly more diffuse atrophy of one hemisphere and areas of high T2 signal. It typically does not have skull changes.
Compensatory osseous thickening with hyperpneumatization of paranasal sinuses is a non-specific response to loss of brain substance which, if asymmetric, can mimic DDMS.
Sturge Weber syndrome is a congenital malformation in which fetal cortical veins fail to develop normally. Although there is clinical overlap with DDMS the characteristic port-wine stain is a distinguishing feature. The imaging features which are sequelae of progressive venous occlusion and chronic venous ischemia are most often unilateral and include progressive cortical atrophy and characteristic tram track calcifications, enlarged ipsilateral choroid plexus and extensive pial enhancement. As the condition progresses there is compensatory thickening of the calvarium and hyperpneumatization of paranasal sinuses.
Hemimegalencephaly is a congenital malformation in which defective cellular organization and neuronal migration results in hamartomatous overgrowth of a hemisphere. Patients typically present with intractable seizures in the first year of life and go on to develop progressive contralateral hemiparesis. Imaging features include an enlarged dysplastic hemisphere, an enlarged ipsilateral lateral ventricle with a straightened and pointed frontal horn, contralateral displacement of the posterior falx and an enlarged and thickened hemicranium.
martedì 4 agosto 2009
There is a non-enhancing heterogeneous T2 hyperintense and T1 hypointense intradural mass displacing the conus and the cauda equina anteriorly. Posterior scalloping of the L1 vertebral body suggests an indolent process. This mass has restricted diffusion.
- Arachnoid cyst
- Neurenteric cyst
- Dermoid cyst
- Peripheral nerve tumors (schwannoma, neurofibroma)
- Neuroepithelial tumors (astrocytoma, ependymoma, etc.)
Diagnosis: Spinal epidermoid
Epidermoid is a benign neoplasm that develops from ectodermal tissue. It may be congenital or acquired. It may be acquired iatrogenically from implantation of viable dermal and epidermal elements following lumbar puncture, surgery, or trauma.
It is often difficult to differentiate between an epidermoid cyst from an arachnoid cyst. DWI and FLAIR are most useful to distinguish the two, because only an epidermoid cyst will have restricted diffusion and signal intensity different from that of CSF.
Epidermoid is a benign neoplasm that is developed out of ectodermal tissue. The capsule is made of a thin layer of squamous epithelium which grossly appears white and pearly and may be smooth, lobulated or nodular. These cysts are filled with desquamated epithelial keratin and cholesterol crystals, grossly appearing as a creamy, waxy material.
Spinal epidermoid cysts are rare, comprising 0.5-1% of intraspinal tumors, but up to 10% of spinal cord tumors in patients under 15 years. Tumors grow slowly until large enough to cause symptoms, usually in early adulthood. Prevalence is greater among males compared with females.
Epidermoid cysts can present as a slowly progressive compressive radiculopathy/myelopathy. Patients may also present with neuropathic bladder, cauda equina syndrome, scoliosis, or chemical meningitis from a ruptured cyst.
Epidermoids may be congenital (60%) or acquired (40%). Congenital epidermoids arise from epidermal rests, and often have associated epidermal defects, such as spina bifida and hemivertebrae. Acquired epidermoids may result from seeding of viable dermal and epidermal elements following lumbar puncture, surgery, or trauma. The link between lumbar puncture and acquired epidermoid cysts is higher when lumbar puncture occurred during the neonatal period. Complete surgical resection offers the best chance of neurologic recovery. Incompletely resected epidermoid cysts tend to recur.