MRI of the Brain

Magnetic resonance imaging ( MRI) is base don the absorption and emission of radiofrequency energy by protons whose spin is influenced by changing magnetic fields ( 0.3 to 1.5 T). Unlike computed tomograohy (CT), there is no radiation exposure.

T1-weighted images cause fat( eg, myelin in the white matter) to appear bright and wáter( eg, cerebrospinal fluid [CSF] or edema) to appear dark on this sequence. The gray –white interfaces of the brain are well depicted on these sequences, esencially if with the images are thinly sliced.

T2-weighted images cause wáter ( eg,CSF and edema) to appear bright and fat to appear dark.

The MRI-based intravenous contrast agents ( eg, gadolinium) are frequently used in T1-weight images to make serum appear bright. The blood-brain barrier typically serves to limit the passage of many molecules out of the blood vessels. If the disease processes break down this barrier ( such as infection, tumors,or inflammation), intravenous contrast agents can cross into the brain, causing áreas of contrast entry to appear very bright.

MRI vs CT

CT can be performed quickly and is preferred in cases of trauma and emergency circunstances. CT is more sensitive for detecting calcification and better delineates cortical bone. CT angiography has better resolution compared with magnetic resonance angiography; however, the latter has the advantage of not absolutely requiring the use of contrast agents. MRI cannot be performed in claustrophobic patients and those with ferromagnetic medical devices, such as pacemakers.Futher, MRI takes longer to perform and might require sedation, precluding its use in emergency situations. However, for evaluating posterior fossa disease, white matter disease, temporal lobe epilepsy, and vascular diseases, MRI is preferable to CT. 

Apart from sparing the effect of radiation; mRI is superior to CT in delinesting extent, spread, mass effect, vascularity, necrosis, and edema. T2-weighted sequences are sensitive for detection of tumor and edema.

MRI is superior to CT when there is suspicion of intracranial extension, optic nerve involvement, and cavernous sinus thrombosis because MRI is better for discerning soft tissue disease. Gadolinium is a paramagnetic contrast agent that prolongs the spin of water protons, resulting in postcontrast enhancement of areas of inflammation on T1-weighted imaging. The most sensitive technique for demonstrating orbital infection is post gadolinium  fat suppressed T1-weight imaging.

FLAIR is an extremely useful technique in brain imaging. Like conventional T2_weighted imaging, edema appears bright, but this technique nulls ( or makes dark) CSF signal. FLAIR is a sensitive technique for displaying demyelination within the brain, thus clearly revealing lesions in proximity to CSF, such as periventricular plaques in multiple sclerosis. The technique is accomplished via a relatively long inversion time to allow the longitudinal magnetization of CSF to return tl the null point preceding the conventional spin echo imaging. It also has a tremendous role in early detection of cortical gray matter infarcts.The cortical gray matter is vulnerable to ischemia because of its high metabolic activity. However, cortical gray matter immediately adjacent to CSF within the sulci makes infarction hard to delineate when this area undergoes conventional imaging sequences that emphasize fluid signal. FLAIR suppress the CSF signal and makes the cortical or periventricular area more conspicuous.

DWI (Diffusion-weighted imaging) was performed by adding 2 strong diffusion-sensitizing magnetic field gradient pulses. DWI depicts recently infarcted brain as very bright signal. The actual diffusion in the tissue is decreased as seen on apparent diffusion can last 5 to 10 days ( but sometimes less) in pediatric population. DWI can detect ischemic stroke within minutes, in contrast to conventional MRI and can distinguish new and old strokes and acute and
chronic ones. Because abscesses, parenchymal contusions, and cysts can also demonstrate restricted diffusion, DWI also helps detect brain abscesses and cystic tumors.

Magnetic resonance spectroscopy monitors biochemical changes in brain tumors, head trauma, stroke, epilepsy, metabolic disorders, and infections. The metabolites predominantly measured are N-acetylaspartato (NAA), creatine, choline, and myoinositol. NAA, an amino acid found exclusively in neurons, is regarded as a nonspecific marker of neuronal viability. NAA levels are decreased in conditions such as infarction and neuronal inflammation. Lactate is absent in normal brain tissue, and its presence is indicative of anaerobic glycolisis at cellular level. Elevated lactate levels are associated with ischemia or metabolic disorders ( with predominant anaerobic glycolisis). An elevated choline-creatine ratio is suggestive of malignancy. Choline is involved in the synthesis of phospholipid cell membranes; in aggressive neoplasms, choline is elevated because of rapid cell turnover.

Pediatrics in Review
Vol.35 No.3 pp.106-111 March 2014 ( esta en biblioteca en la parte de atrás, revistas nuevas)

DEMENCIA

Memory impairment is often prominent as an early symptom. Patients may experience difficulty learning new material or remembering recent conversations or events, and they may misplace valuables, such as keys, or forget to turn off the stove. In more severe dementia, patients also forget previously learned material, including the names of loved ones. Disturbances in spatial abilities, expressive or receptive language, and executive functions.

To receive a diagnosis of dementia a patient must have cognitive deficits that are sufficiently severe to cause impairment in daily functioning and that represent a change from a previous level of functioning.

The prevalence rate of Creutzfeldt-Jakob disease (CJD) for example, is 1 in 1 million. Although rare CJD generates interest because of media attention to the bovine spongiform encephalopathy, or " mad cow".

Alzheimer´s disease is a neurodegenerative disorder characterized by progressive cognitive decline and a broad spectrum of brain pathology, including accumulation of fibrillar amyloid-B protein in plaques and vessels, neurofibrillary tangles, and synaptic and neuronal loss.

In contrast, dementia caused by cerebrovascular disease is often associated with an abrupt onset.

The term vascular dementia (VaD) actually comprises several heterogeneous syndromes, including cortical ( multiinfarct) demetia and noninfarct vascular demetia. And because evidence suggests that small stokes or risk factors for vascular disease may lead to increased clinical expression of AD. Comorbility of AD and VaD is especially common in the very old.

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In AD, plaques develop in the hippocampus, a structure deep in the brain that helps to encode memories, and in other areas of the cerebral cortex that are used in thinking and making decisions.

In a cross-sectional study of 48 AD patients without diabetes, 20 cognitively normal diabetic patients, 16 patients with frontotemporal dementia, and 84 cognitively normal controls, researchers found that dysfunctionally phosphorylated insulin receptor substrate-1 (IRS-1), a neuronal protein, is detectable in blood using exosome-based technology and may be able to predict AD up to 10 years before the appearance of symptoms.

Compared with all other groups, patients with AD had several-fold higher p-Ser312-IRS-1 and Ser312/p-panY ratios and lower p-panY-IRS-1

Mild Alzheimer disease

Signs of mild AD can include the following:

• Memory loss
• Confusion about the location of familiar places
• Taking longer to accomplish normal, daily tasks
• Trouble handling money and paying bills
• Compromised judgment, often leading to bad decisions
• Loss of spontaneity and sense of initiative
• Mood and personality changes; increased anxiety
  
  
  
  

  Moderate Alzheimer disease

  The symptoms of this stage can include the following:

  • Increasing memory loss and confusion
  • Shortened attention span
  • Problems recognizing friends and family members
  • Difficulty with language; problems with reading, writing, working with numbers
  • Difficulty organizing thoughts and thinking logically
  • Inability to learn new things or to cope with new or unexpected situations
  • Restlessness, agitation, anxiety, tearfulness, wandering, especially in the late afternoon or at night
  • Repetitive statements or movement; occasional muscle twitches
  • Hallucinations, delusions, suspiciousness or paranoia, irritability
  • Loss of impulse control: Shown through behavior such as undressing at inappropriate times or places or vulgar language
  • Perceptual-motor problems: Such as trouble getting out of a chair or setting the table

Severe Alzheimer disease

Patients with severe AD cannot recognize family or loved ones and cannot communicate in any way. They are completely dependent on others for care, and all sense of self seems to vanish.

Other symptoms of severe AD can include the following:

• Weight loss
• Seizures, skin infections, difficulty swallowing
• Groaning, moaning, or grunting
• Increased sleeping
• Lack of bladder and bowel control

In end-stage AD, patients may be in bed much or all of the time. Death is often the result of other illnesses, frequently aspiration pneumonia.

Diagnosis

Means of diagnosing AD include the following:

• Clinical examination: The clinical diagnosis of AD is usually made during the mild stage of the disease, using the above-listed signs
• Lumbar puncture: levels of tau and phosphorylated tau in the cerebrospinal fluid are often elevated in AD, whereas amyloid levels are usually low; at present, however, routine measurement of CSF tau and amyloid is not recommended except in research settings
• Imaging studies: Imaging studies are particularly important for ruling out potentially treatable causes of progressive cognitive decline, such as chronic subdural hematoma or normal-pressure hydrocephalus
  
  

  Blood Studies

  Laboratory tests can be performed to rule out other conditions that may cause cognitive impairment. Current recommendations from the American Academy of Neurology (AAN) include measurement of the cobalamin (vitamin B12) level and a thyroid function screening test. 

  There is a possible link between vitamin D deficiency and cognitive impairment.However, vitamin D deficiency has not been identified as a reversible cause of dementia.
  
  

  

  

  

  

Pathophysiology

Dementia with Lewy bodies

Recent findings indicate that the presence of visual hallucinations and agnosia in the course of a dementing illness can help distinguish DLB from AD.

Pick´s disease and other frontal lobe dementias are fairly rare and are characterized in their early stages by changes in personality, executive dysfunction, deterioration of social skills, emotional blunting, behavioral desinhibition, and language abnormalities. 

Structural brain imaging of patients with Pick´s disease typically reveals prominent frontal or temporal atrophy or both, with relative sparing of the parietal and occipital lobes. The diagnosis is confirmed by autopsy finding of Pick inclusion bodies.

Normal pressure hydrocephalus (NPH), also known as non obstructive or communicating hydrocephalus, is somewhat of a misnomer, falsely suggesting that intracranial pressure  is always normal in this condition when in fact there can be elevation in ICP. 

NPH is associated with a classic triad of dementia, gait disturbance, and urinary incontinence.

The most common form of substance-induced persisting dementia is caused by alcohol. The Wernicke-Korsakoff syndrome  consists of two phases. The first is a potentially reversible Wernicke encephalopathy characterized by a confused state, gait ataxia, and eye movement abnormalities. <If left untreated with large doses of thiamine, a chronic Korsakoff state follows, characterized by severe anterograde and retrograde amnesia, and executive deficits, apathy, and disinterest in alcohol. Wernicke-Korsakoff syndrome usually arises in a context of persistent alcohol abuse and poor nutrition.

Memory impairment is a hallmark of dementia and is required to make a diagnosis. Dementia is distinguished from amnestic disorder by the involvement of additional cognitive deficits ( e.g.. language, visuospatial processing, problem solving). Although dementia and delirium both include global cognitive impairment, delirium is characterized by prominent deficits in attention and awareness of the environment , and the symptoms typically develop rapidly and fluctuate in severity. Dementia often co-occurs with depression or depressive symptoms, but depression alone can cause significant cognitive impairment that is difficult to distinguish from dementia.

CAPSULAS DE CONOCIMIENTO

TRAUMA CRANEAL, HIPERTENSION INTRACRANEAL, TUMORES INTRACRANEALES

Tema 5. Conocer la fisiología y fisiopatología de la dinámica de fuerzas observada en el cráneo así como la intervención de los vectores de fuerza, masa encefálica, presión de LCR y demás mecanismos que se ven afectados en el Síndrome de hipertensión intracraneal.

Objetivos de aprendizaje:

1. Describir el mecanismo de producción y flujo de líquido cefaloraquídeo en el sisterma nerviosos central.

2. Mencionar las características del líquido cefaloraquídeo

3. Explicar la función de las meninges

4. Explicar los mecanismos por los cuales se presenta aumento en la presión intracraneal

5. Describir los síntomas y signos de aumento de presión intracraneal y su mecanismo

6. Conocer los principales diagnósticos que presental aumento de la presión intracreaneal

7. Denifir el concepto de efecto de masa en un tumor o masa intracraneal

8. Conocer la clasificación de traumatismo craneal y los elementos clínicos que se utilizan para establecer los diferentes niveles o grados

9. Describir los diferentes tipos de hemorragias intracraneales así como los datos clínicos encontrados en los pacientes que presentan esta situación

10. Comprender los términos de Resonancia Magnética como son T1 y T2 así como Flair, etc.

11. Conocer el abordaje diagnóstico y terapéutico de los pacientes con hipertensión intracraneal según las guías clínicas

12. Enlistar las situaciones donde un paciente con traumatismo craneal requiere manejo quirurgico

Temblor.-

Es el trastorno del movimiento más frecuente de todos, no es raro en la niñez y es generalmente benigno. Es un movimiento involuntario, oscilatorio, rítmico y más o menos regular, de una parte del cuerpo, que se produce alrededor de un punto de fijación por contracciones de músculos antagonistas recíprocamente intervalos. Su ritmicidad lo diferencia de otros movimientos involuntarios y su carácter bifásico lo distingue del cono, pues lo causan contracciones repetidas y alternantes de grupos musculares opuestos.

De acuerdo con su expresión clínica, el temblor puede dividirse en dos grandes categorías : 1) De reposo, es decir en ausencia de movimiento voluntario y 2) De acción, que a su vez se puede subdividir en : A) postura, es decir que ocurre cuando el sujeto mantiene una postura antigravitatoria ( maniobra de Barré) o sostiene una contracción voluntaria, y B) Cinético o de intención, que ocurre durante el movimiento dirigido a una meta o para una acción específica como sería el escribir a mano.

Temblor de reposo.- El típico temblor de reposo es el parkinsoniano; es rítmico, amplio, con frecuencia de 3 a 7 Hz. El temblor está casi siempre localizado en una o ambas manos, es menos común en los pies, la mandíbula, los labios o la lengua, ocurre cuando la extremidad está en reposo y se suprime o disminuye, al menos momentáneamente, durante los movimientos voluntarios de la parte afectada, para reaparecer cuando la extremidad reposa en su nueva posición. Puede observarse en niños y adolescentes en el parkinsonismo inducido por fármacos tales como los derivados de la fenotiazina y de la butirofenona. Se bloquea eficazmente el temblor con el triexifenidil, con otros fármacos anticolinérgicos y también pero menos eficazmente con la L-Dopa.

Temblor Fisiologico.- 
El temblor fisiológico es la forma más frecuente de temblor postura; es normal y no requiere manejo médico. La frecuencia del temblor fisiológico varía de 8-12 Hz. en las manos y es de 6.5 Hz. en otras partes del cuerpo.

Corea

El término corea se deriva del término griego que significa "baile". Esta consiste en movimientos involuntarios, continuos, irregulares, no sostenidos, breves y abruptos, que fluyen al azar de una parte del cuerpo a otra, El paciente puede parcial y temporalmente suprimir la corea y frecuentemente disminuirla al incorporar el movimiento anormal en una actividad o movimiento con un semipropósito ( apariencia). En ocaciones el movimiento puede adquirir características exageradas y grotescas. Otras expresiones de corea pueden ser protrusión rápida e involuntaria de la len¡gua, muecas faciales y sonidos por exhalaciones ruidosas. La marcha frecuentemente es irregular simulando una danza.

Balismo
Es una forma de corea con movimientos de gran amplitud que generalmente afectan solo un lado del cuerpo, de aquí el término de hemibalismo. Tiende  a afectar los músculos próximales ( generalmente los de los hombros y algunas veces los de la cadera). El movimiento de la extremidad puede ser violento pareciendo hacer un lanzamiento con la extremidad afectada, que puede llegar a causar luxación del hombro. Los movimientos son irregulares y generalmente desaparecen durante el sueño.

Atetosis.- Este  término se deriva de la palabra griega que significa "cambiante" o "no fijo". La condice´on se caracteriza por incapacidad de sostener en una posición los dedos de las manos o pies, cara lengua y otras partes del cuerpo. La postura es interrumpida por movimientos relativamente lentos, sinuosos y sin propósito, que tienen la tendencia a fluir de un lado a otro. Cuando estos movimientos son breves se fusionan con la corea ( coreoatetosis). Cuando los movimientos son sostenidos en el punto máximo de contracción se fusionan con la disponía y el termino disponía atetósica se puede aplicar..

Síndrome neuroléptico maligno.-

Este síndrome se caracteriza por la triada de fiebre, signos de disfunción autonómica ( palidez, diaforesis, inestabilidad de presión arterial, taquicardia, congestión pulmonar, taquipnea) y movimientos anormales ( aquinesia, hipertonía y disquinesia); no es raro que se agregue, estupor, coma y muerte. El tratamiento requiere la suspensión del neuroléptico y medidas vitales adecuadas.

Acatisia aguda.- es una sensación interna de inquietud con la que el paciente siente la urgencia de moverse, cambiar de psicosis, levantarse, caminar, sentarse, y volver a  levantarse, correr, marchar sin moverse del mismo lugar, cruza y destrozar las piernas o los brazos, mecer el tronco, y movimientos más complejos de las manos como frotárselas o rascárselas. Estos aparecen cuando se está incrementando la dosis de fármacos neurolépticos o con la administración de Levodopa y pueden ocurrir a cualquier edad.

Disquinesia tardía.- es un efecto secundario de los neurolépticos ( antipsicóticos y tranquilizantes mayores), es un trastorno hiperquinético del movimiento, caracterizado por movimientos coreoatetósicos, balísticos y distintos del tronco, las extremidades y la musculatura de la cara, especialmente buco-lingual