Advantage of magnetic resonance imaging in the diagnosis of cerebral infections

Can we forecast poor outcome in herpes simplex and varicella zoster encephalitis? A narrative review

Herpes simplex virus (HSV) and varicella zoster virus (VZV) are among the most commonly diagnosed infectious causes of sporadic encephalitis worldwide. Despite treatment, mortality and morbidity rates remain high, especially for HSV encephalitis. This review is intended to provide an overview of the existing scientific literature on this topic from the perspective of a clinician who is confronted with serious decisions about continuation or withdrawal of therapeutic interventions. We performed a literature review searching two databases and included 55 studies in the review. These studies documented or investigated specifically outcome and predictive parameters of outcome of HSV and/or VZV encephalitis. Two reviewers independently screened and reviewed full-text articles meeting the inclusion criteria. Key data were extracted and presented as a narrative summary. Both, HSV and VZV encephalitis have mortality rates between 5 and 20% and complete recovery rates range from 14 to 43% for HSV and 33 to 49% for VZV encephalitis. Prognostic factors for both VZV and HSV encephalitis are older age and comorbidity, as well as severity of disease and extent of magnetic resonance imaging (MRI) lesions on admission, and delay in treatment initiation for HSV encephalitis. Although numerous studies are available, the main limiting factors are the inconsistent patient selection and case definitions as well as the non-standardised outcome measures, which hampers the comparability of the studies. Therefore, larger and standardised observational studies applying validated case definitions and outcome measures including quality of life assessment are required to provide solid evidence to answer the research question.

Diagnosing viral encephalitis and emerging concepts

PURPOSE OF REVIEW

This review offers a contemporary clinical approach to the diagnosis of viral encephalitis and discusses recent advances in the field. The neurologic effects of coronaviruses, including COVID-19, as well as management of encephalitis are not covered in this review.

RECENT FINDINGS

The diagnostic tools for evaluating patients with viral encephalitis are evolving quickly. Multiplex PCR panels are now in widespread use and allow for rapid pathogen detection and potentially reduce empiric antimicrobial exposure in certain patients, while metagenomic next-generation sequencing holds great promise in diagnosing challenging and rarer causes of viral encephalitis. We also review topical and emerging infections pertinent to neuroinfectious disease practice, including emerging arboviruses, monkeypox virus (mpox), and measles.

SUMMARY

Although etiological diagnosis remains challenging in viral encephalitis, recent advances may soon provide the clinician with additional tools. Environmental changes, host factors (such as ubiquitous use of immunosuppression), and societal trends (re-emergence of vaccine preventable diseases) are likely to change the landscape of neurologic infections that are considered and treated in clinical practice.

Progress on Diagnosis of Tuberculous Meningitis

Central nervous system (CNS) disease caused by Mycobacterium tuberculosis (MTB) is highly devastating. Tuberculous meningitis (TBM) is the most common form of CNS tuberculosis (TB). Rapid, sensitive, and affordable diagnostic tests are not available. Ziehl-Neelsen (ZN) stain has a very low sensitivity in cases of TBM, the sensitivity rates is of about 10-20%.The detection rate can be improved by taking large volume CSF samples (>6 ml) and prolonged slide examination (30 min). Culture of MTB from the CSF is slow and insufficiently sensitive. The sensitivity is different, which varies from 36% to 81.8%. The microscopic observation drug susceptibility (MODS) assay was recommended by the World Health Organization in 2011. The sensitivity is 65%, which is more sensitive and faster than CSF smear. Commercial PCR assays were found to be insensitive at detecting MTB in CSF samples. Many research provided the value of ADA on the TBM diagnosis. Interferon-gamma release assays (IGRAs) are not recommended for diagnosis of active TB disease. Imaging is essential in diagnosis and showing complications of CNS TB. Thwaites criteria and the Lancet consensus scoring system (LCSS) were developed to improve the diagnosis of TBM. Clinicians will continue to make judgment based on clinical examination, inflammatory CSF examinations, imaging studies, and scoring systems.

Managing atypical and typical herpetic central nervous system infections: results of a multinational study

There have been many studies pertaining to the management of herpetic meningoencephalitis (HME), but the majority of them have focussed on virologically unconfirmed cases or included only small sample sizes. We have conducted a multicentre study aimed at providing management strategies for HME. Overall, 501 adult patients with PCR-proven HME were included retrospectively from 35 referral centres in 10 countries; 496 patients were found to be eligible for the analysis. Cerebrospinal fluid (CSF) analysis using a PCR assay yielded herpes simplex virus (HSV)-1 DNA in 351 patients (70.8%), HSV-2 DNA in 83 patients (16.7%) and undefined HSV DNA type in 62 patients (12.5%). A total of 379 patients (76.4%) had at least one of the specified characteristics of encephalitis, and we placed these patients into the encephalitis presentation group. The remaining 117 patients (23.6%) had none of these findings, and these patients were placed in the nonencephalitis presentation group. Abnormalities suggestive of encephalitis were detected in magnetic resonance imaging (MRI) in 83.9% of the patients and in electroencephalography (EEG) in 91.0% of patients in the encephalitis presentation group. In the nonencephalitis presentation group, MRI and EEG data were suggestive of encephalitis in 33.3 and 61.9% of patients, respectively. However, the concomitant use of MRI and EEG indicated encephalitis in 96.3 and 87.5% of the cases with and without encephalitic clinical presentation, respectively. Considering the subtle nature of HME, CSF HSV PCR, EEG and MRI data should be collected for all patients with a central nervous system infection.

Herpes simplex encephalitis in Iceland 1987-2011

Herpes simplex encephalitis (HSE) is a serious disease with 10-20% mortality and high rate of neuropsychiatric sequelae. This study is a long-term, nationwide study in a single country, Iceland. Clinical data were obtained from patient records and from DNA PCR and antibody assays of CSF. Diagnosis of HSE was classified as definite, possible or rejected based on symptoms, as well as virological, laboratory and brain imaging criteria. A total of 30 definite cases of HSE were identified during the 25 year period 1987-2011 corresponding to incidence of 4.3 cases/106 inhabitants/year. Males were 57% of all patients, median age 50 years (range, 0-85). Fever (97%), cognitive deficits (79%), impaired consciousness (79% with GCS < 13), headache (55%) and seizures (55%) were the most common symptoms. Brain lesions were found in 24 patients (80%) by MRI or CT. All patients received intravenous acyclovir for a mean duration of 20 days. Three patients (10%) died within one year and 21/28 pts (75%) had a Karnofsky performance score of <70% with memory loss (59%), dysphasia (44%), frontal symptoms (44%) and seizures (30%) as the most frequent sequelae. Mean delay from onset of symptoms to treatment was 6 days; this was associated with adverse outcome. In conclusion, the incidence of `HSE is higher than recently reported in a national registry study from Sweden. Despite advances in rapid diagnosis and availability of treatment of HSE, approximately three of every four patients die or are left with serious neurological impairment.

Diagnosis and management of acute encephalitis: A practical approach

Encephalitis results in considerable morbidity and mortality in the United States and worldwide. Neurologists are often consulted or directly care for patients with encephalitis admitted to the hospital and must be able to discriminate between encephalitis and the many conditions that mimic it. Moreover, neurologists must be familiar with the myriad causes of encephalitis in order to develop a practical approach to diagnostic testing and treatment. An understanding of recent advances in management, particularly with respect to autoimmune etiologies and critical care approaches, is equally important. Here, we summarize a general approach to the care of adult patients with encephalitis.

Viral meningoencephalitis: a review of diagnostic methods and guidelines for management

BACKGROUND

Viral encephalitis is a medical emergency. The prognosis depends mainly on the pathogen and host immunologic state. Correct immediate diagnosis and introduction of symptomatic and specific therapy has a dramatic influence upon survival and reduces the extent of permanent brain injury.

METHODS

We searched the literature from 1966 to 2009. Recommendations were reached by consensus. Where there was lack of evidence but consensus was clear, we have stated our opinion as good practice points.

RECOMMENDATIONS

Diagnosis should be based on medical history and examination followed by CSF analysis for protein and glucose levels, cellular analysis, and identification of the pathogen by polymerase chain reaction amplification (recommendation level A) and serology (level B). Neuroimaging, preferably by MRI, is essential (level B). Lumbar puncture can follow neuroimaging when immediately available, but if this cannot be performed immediately, LP should be delayed only under unusual circumstances. Brain biopsy should be reserved only for unusual and diagnostically difficult cases. Patients must be hospitalized with easy access to intensive care units. Specific, evidence-based, antiviral therapy, acyclovir, is available for herpes encephalitis (level A) and may also be effective for varicella-zoster virus encephalitis. Ganciclovir and foscarnet can be given to treat cytomegalovirus encephalitis, and pleconaril for enterovirus encephalitis (IV class evidence). Corticosteroids as an adjunct treatment for acute viral encephalitis are not generally considered to be effective, and their use is controversial, but this important issue is currently being evaluated in a large clinical trial. Surgical decompression is indicated for impending uncal herniation or increased intracranial pressure refractory to medical management.

Discontinuation of maintenance therapy against toxoplasma encephalitis in AIDS patients with sustained response to anti-retroviral therapy

Discontinuation of maintenance therapy against toxoplasma encephalitis (TE) for individuals infected with human immunodeficiency virus (HIV) who are receiving successful anti-retroviral therapy is considered safe. Nevertheless, there are few published studies concerning this issue. Within the setting of the Swiss HIV Cohort Study, this report describes a prospective study of discontinuation of maintenance therapy against TE in patients with a sustained increase of CD4 counts to > 200 cells/microL and 14% of total lymphocytes, and no active lesions on cerebral magnetic resonance imaging (MRI). In addition to clinical evaluation, cerebral MRI was performed at baseline, and 1 and 6 months following discontinuation. Twenty-six AIDS patients with a history of TE agreed to participate, but three patients (11%) could not be enrolled because they still showed enhancing cerebral lesions without a clinical correlate. One patient refused MRI after 6 months while clinically asymptomatic. Among the remaining 22 patients who discontinued maintenance therapy, one relapsed after 3 months. During a total follow-up of 58 patient-years, there was no TE relapse among the patients who had remained clinically and radiologically free of relapse during the study. Thus, discontinuation of maintenance therapy against TE was generally safe, but may fail in a minority of patients. Patients who remain clinically and radiologically free of relapse at 6 months after discontinuation are unlikely to experience a relapse of TE.

Viral encephalitis: a review of diagnostic methods and guidelines for management

Viral encephalitis is a medical emergency. The spectrum of brain involvement and the prognosis are dependent mainly on the specific pathogen and the immunological state of the host. Although specific therapy is limited to only several viral agents, correct immediate diagnosis and introduction of symptomatic and specific therapy has a dramatic influence upon survival and reduces the extent of permanent brain injury in survivors. We searched MEDLINE (National Library of Medicine) for relevant literature from 1966 to May 2004. Review articles and book chapters were also included. Recommendations are based on this literature based on our judgment of the relevance of the references to the subject. Recommendations were reached by consensus. Where there was lack of evidence but consensus was clear we have stated our opinion as good practice points. Diagnosis should be based on medical history, examination followed by analysis of cerebrospinal fluid for protein and glucose contents, cellular analysis and identification of the pathogen by polymerase chain reaction (PCR) amplification (recommendation level A) and serology (recommendation level B). Neuroimaging, preferably by magnetic resonance imaging, is an essential aspect of evaluation (recommendation level B). Lumbar puncture can follow neuroimaging when immediately available, but if this cannot be obtained at the shortest span of time it should be delayed only in the presence of strict contraindications. Brain biopsy should be reserved only for unusual and diagnostically difficult cases. All encephalitis cases must be hospitalized with an access to intensive care units. Supportive therapy is an important basis of management. Specific, evidence-based, anti-viral therapy, acyclovir, is available for herpes encephalitis (recommendation level A). Acyclovir might also be effective for varicella-zoster virus encephalitis, gancyclovir and foscarnet for cytomegalovirus encephalitis and pleconaril for enterovirus encephalitis (IV class of evidence). Corticosteroids as an adjunct treatment for acute viral encephalitis are not generally considered to be effective and their use is controversial. Surgical decompression is indicated for impending uncal herniation or increased intracranial pressure refractory to medical management.

Acute encephalitis associated with measles: MRI features

We document the MRI features in six patients aged 5-14 years with acute encephalitis following measles. The diagnosis was made on a characteristic morbiliform rash and detection of specific IgM and IgG antibodies. The symptoms of encephalitis occurred 1-11 days after the appearance of the rash. All patients underwent MRI within 1-4 days of the onset of neurological symptoms. Diffusion weighted images (DWI) were obtained in three patients. In all patients, T2-weighted images showed widely distributed, multifocal high signal in both cerebral hemispheres with swelling of the cortex, with bilateral, symmetrical involvement of the putamen and caudate nucleus. The lesions had showed low apparent diffusion coefficients. Three patients showed subacute gyriform haemorrhage, and asymmetrical gyriform contrast enhancement on follow-up MRI.

Nocardia brain abscess misinterpreted as cerebral infarction

We present the case of a non-immunocompromised man with right-sided hemiparesis and aphasia thought to be caused by cerebral infarction, but which in the later clinical course evolved to be a nocardia brain abscess that needed surgical intervention. Misinterpretation of imaging combined with the absence of clinical signs of infection led to inadequate primary treatment

Central nervous system: review of clinical use of contrast media

The clinical utility of intravenous contrast administration for magnetic resonance imaging in neoplastic disease of the brain, non-neoplastic disease of the brain, and in disease of the spine is reviewed. Magnetic resonance imaging (MRI) is the modality of choice for the evaluation of most suspected intracranial and spinal pathology. Contrast use substantially improves lesion detection and differential diagnosis. Applications are discussed in neoplastic disease, infection, vascular disorders, demyelinating disease, and trauma (specifically including in the spine disk herniation). Gadolinium chelates play as important a role in magnetic resonance imaging as do iodinated agents in computed tomography. Contrast administration facilitates time-efficient and cost-effective diagnosis.

[Alternative diagnoses among suspected herpes simplex encephalitis patients with negative polymerase chain reaction]

The aim of this study was to analyze the diagnosis found in a series of patients in which the diagnosis of Herpes simplex encephalitis (HSE) was ruled out by a negative polymerase chain reaction (PCR) result for HSV DNA in cerebrospinal fluid (CSF) samples. Forty three out of 61 HSE suspected patients had negative PCR. An alternative diagnosis was established in 41.9% of these patients. These patients were diagnosed as having viral (2 cases-11.1%) and non viral (5 cases-27.2%) CNS infections, vascular (4 cases-22.2%) and demyelinating diseases (3 cases-16.7%), metabolic disturbances (3 cases-16.7%), and CNS tumor (1 case-5.6%). The non specific clinical presentation of this disease and the availability of an efficient treatment for HSE explain why several patients with other diseases were initially treated with acyclovir. The early use of PCR in CSF was considered essential for the evaluation of the acute encephalitis cases in this study.

Magnetic resonance imaging features of brain stem abscessation in two cats

Premortem magnetic resonance imaging (MRI) was performed in two cats with brain stem abscessation confirmed post mortem by histology and recovery of multiple bacterial species. The MRI features of the abscesses were distinctive and included a thick and marked enhancement of the abscess capsule and extension of the lesion from a tympanic bulla in one cat. A focal area of increased signal intensity was present on T2-weighted images. A circumscribed area of decreased signal intensity was surrounded by a ring of increased signal intensity on precontrast T1-weighted images. A center of decreased signal intensity with a thick, markedly enhanced abscess capsule was observed on post contrast T1-weighted images. These findings are compared to the current experimental and clinical literature of brain abscess. The underlying pathogenesis of MRI features is reviewed.

MR imaging of solitary pulmonary lesion: emphasis on tuberculomas and comparison with tumors

The aim of this study was to determine whether solitary pulmonary tuberculoma and malignant tumor can be differentiated on the basis of magnetic resonance (MR) signal intensity. Twenty-eight patients with solitary pulmonary lesions were prospectively studied with MR imaging: T1-weighted, enhanced T1-weighted, proton density-weighted, and T2-weighted spin echo images were obtained. The confirmation methods used were computed tomography (CT)-guided biopsy in seven patients with lung cancer and four patients with tuberculosis; surgery in ten patients with lung cancer and five patients with tuberculosis; and laboratory data in two patients with tuberculosis. Morphologic features and MR signal intensity were examined in detail. As the test for detection of tuberculoma, signal difference on T2-weighted images was carefully analyzed. The signal intensity ratio of the nodule to thoracic muscle signal intensity was measured. The signal intensities obtained from the lung cancers and tuberculomas were variable on pre-and post-enhanced T1-weighted images and proton density-weighted images. Masses were hypointense in 2 of 17 patients with lung cancer and in 9 of 11 patients with tuberculoma on T2-weighted images (sensitivity 82%, specificity 89%, accuracy 87%). The mean signal intensity ratios of the tuberculomas to muscle were significantly lower than those of malignant tumors on T1-weighted, enhanced T1-weighted, proton density-weighted, and T2-weighted images (P < 0.0001). After gadolinium-DTPA enhancement, 2 malignant tumors and 7 tuberculomas showed a marginal rim enhancement pattern, whereas 15 malignant tumors and 2 tuberculomas revealed a diffuse enhancement. The results of MR imaging were consistent with those of CT in 84% of the patients. MR imaging is a helpful adjunctive method in terms of differentiating a tuberculoma from a malignant tumor.

Tuberculous meningitis in native Dutch children: a report of four cases

Although it is believed that in the western countries tuberculosis is a disease confined to high-risk groups such as immigrants, we describe four cases of tuberculous meningitis (TBM) in native Dutch children. The inverse relation between the delay in starting therapy and the clinical outcome makes early diagnosis of TBM essential. The often non-specific presenting symptoms and laboratory results, the time-consuming character of cultures and the unfamiliarity of western medical staff with the disease all may contribute to a delay in diagnosis of TBM. We believe that especially gadolinium-enhanced MRI or contrast-enhanced CT can be very helpful in the early diagnosis. Although not specific, hydrocephalus and basal meningeal enhancement on MRI or CT, together with the clinical suspicion can suggest the diagnosis to such an extent that there is enough reason to start antituberculous treatment.

Magnetic resonance imaging of the corticospinal tracts in amyotrophic lateral sclerosis

In 13 patients with amyotrophic lateral sclerosis (ALS), corticospinal tract lesions on spinal cord, brain and brain stem were examined by MR imaging. In 9 patients, areas of high signal intensity located in the dorsolateral columns coinciding with the lateral corticospinal tracts, were detected on axial T2*-weighted MR imaging of the cervical spinal cord using a gradient echo technique. In two patients, these spinal cord MR abnormalities corresponded well to the postmortem pathological findings of lateral corticospinal tract degeneration. T2-weighted abnormal MR signals along the corticospinal tract at the brain and brain stem were detected in 4 patients, all of whom also showed abnormal signals on cervical cord MR imaging. Four of 13 patients did not show any abnormal signals on brain and brain stem or spinal cord MR imaging. Spinal cord MR imaging provides a useful information regarding upper motor neuron lesions in ALS.

MRI in subacute combined degeneration

We describe a patient with clear lesions in the spinal cord on MRI due to subacute combined degeneration. T2-weighted images clearly showed abnormal high signals in the posterior columns, which disappeared on recovery from the disease.

Serial neuroradiological studies in focal cerebritis

We report serial neuroradiological studies in a patient with focal cerebritis in the head of the left caudate nucleus. On the day after the onset of symptoms, CT showed an ill-defined low density lesion. The lack of contrast enhancement appeared to be the most important finding for differentiating focal cerebritis from an encapsulated brain abscess or a tumour. MRI two days later revealed the centre of the lesion to be of slightly low intensity on T1-weighted inversion recovery (IR) images and very low intensity on T2-weighted spin echo images, which appeared to correspond to the early cerebritis stage of experimentally induced cerebritis and brain abscess. Ten days after the onset of symptoms, CT revealed a thin ring of enhancement in the head of the caudate nucleus, and a similar small ring was seen in the hypothalamus 16 days after the onset, corresponding to the late cerebritis stage. MRI nine days later revealed ill-defined high signal lesions within the involved area on the T1-weighted IR images. To our knowledge, this is the first published MRI documentation of the early cerebritis stage developing into an encapsulated brain abscess. The mechanisms underlying of these radiographic changes are discussed.

Value of serum anti-herpes simplex viral IgM antibody testing in empirical antiviral treatment of herpes simplex encephalitis

Early antiviral treatment is important for herpes simplex encephalitis. A reliable test for supporting empirical therapy with antiviral agents is urgently needed. Sixty-six children with fever, focal seizures, and consciousness disturbance had their sera examined for anti-herpes simplex viral immunoglobulin M (IgM) antibody with enzyme-linked immunosorbent assay. The result was positive in all seven patients confirmed to have herpes simplex encephalitis. Only two of the other 59 patients were positive on this test. The average period for the development of serologic positivity was 7.3 days from the onset of neurologic symptoms. Although most sera were not tested in the early stage, all were collected on admission day. Our data suggest that before further evidence indicates another diagnosis, this simple, but specific IgM antibody test could be used as a guide for deciding to continue the antiviral treatment for serologically positive cases or to discontinue antiviral treatment for serologically negative ones. Yet, we would not suggest diagnosing herpes simplex encephalitis with this test alone.

MRI in tuberculous meningoencephalitis: report of four cases and review of the neuroimaging literature

The contribution of MRI is reported in four adult patients with tuberculous meningoencephalitis (TbM) and with autopsy correlation in one. Contrast-enhanced T1-weighted MRI revealed the characteristic basal meningeal inflammation of TbM and its focal spreading into adjacent brain. Mixed and T2-weighted pulse sequences delineated a plethora of parenchymal abnormalities. Their relation to TbM was established by a close matching of the patient's neurological findings, contrast enhancement or a change in lesion size. The latter accurately reflected the clinical course in all patients. It remained difficult, however, to distinguish between ischaemic and inflammatory changes, which in some locations were intermixed even histologically. From our experience and that of other groups, MRI provides more diagnostic information in TbM than CT. Moreover, MRI promises to be a useful tool for monitoring treatment response.

Magnetic resonance imaging in herpes simplex encephalitis

Four patients with clinical and serologically proven Herpes Simplex Encephalitis (HSE) were examined by Magnetic Resonance Imaging (MRI) following Computed Tomographic (CT) scans. MRI proved more sensitive at detecting the temporal lobe abnormalities than CT and invariably showed the lesions to be more extensive than suspected. The findings were consistent with an acute inflammatory process. Haemorrhage was present in only one patient. The sharp transition to normal at the lentiform nucleus previously described on CT was present in only one of the four patients, but was observed in a different patient with cerebral lymphoma and no evidence of HSE and is thus concluded to be less specific than previously thought. A repeat MRI scan at seven months on one of the patients showed persisting increased signal on T2 weighted images after resolution of the mass effect. The pathology and suspected mechanisms for the MRI appearances are discussed. MRI is concluded to be a valuable tool in the early diagnosis of HSE and in the longer term for further evaluation of residual disabilities.

Brain abscess in Saudi Arabia

There are significant variations among countries in the incidence of brain abscess. We report here 26 cases of brain abscess treated at the Neurosurgery Department of King Faisal University and Dammam Central Hospital Saudi Arabia over a six year period (1982-1988). This is 2.3% of total admissions to the two neurosurgery departments serving a population of approximately 1.2 million in the same period. Young males were most often affected (M/F ratio 3.3:1; 31% were less than 15 years old, 46% aged between 15-39 years, and 23% older than 40 years). Streptococcus was found to be the most common microorganism (38.4%). Mixed infection was seen in 15.3%, and sterile abscesses were found in 11.5% of the patients after aerobic and anaerobic cultures of the pus. Chronic otitis media and paranasal sinusitis predisposed the patients to abscess formation in 57.6% of the cases. The temporo-parietal area was the commonest site. Epilepsy was a complication in 30.7% of our patients, and the mortality rate was 15.3%.

A follow-up study by CT and MRI in 3 cases of Japanese encephalitis

A follow-up study by CT and MRI in 3 cases of Japanese encephalitis (JE) was performed. Neurologically dementia, forced laughing, tetraplegia and parkinsonism were observed as sequelae. In the CT and MR scans about 3 years after the onset of JE, low-density areas (LDAs) or abnormal signal intensities had remained in the thalamus and basal ganglia. The abnormalities were also found in the brain stem. When the main lesions shown by CT and MRI were compared with those of the acute stage, T2-weighted MRI clearly revealed multiple small areas with high signal intensities, although those in the acute stage had shown diffuse abnormal signals. These findings may be useful in helping to identify JE a long time after the onset.

Gd-DTPA enhanced MR imaging in intracranial tuberculosis

Twenty-six patients with intracranial tuberculosis (Tb) (10 with acute meningitis, 5 with chronic meningitis, 5 with meningitic sequelae and 6 with localized tuberculoma(s)) were examined with MR before and after Gd-DTPA enhancement (0.1 mmol/kg), using 2.0T superconducting unit, and the images were retrospectively analyzed and compared with CT scans. Without Gd-DTPA enhancement, the MR images were generally insensitive to detection of active meningeal inflammation and granulomas. The signal intensity of granulomas was usually isointense to gray matter on both T1- and T2-weighted images, whether they were associated with diffuse meningitis or presented as localized tuberculoma(s). A few granulomas showed focal hypointensity on T2-weighted images. Calcifications seen on CT of the meningitic sequelae group usually appeared markedly hypointense on all spin-echo sequences. On Gd-DTPA enhanced T1-weighted images, abnormal meningeal enhancement indicating active inflammation was conspicuous, and the granulomas often appeared as conglomerated ring-enhancing nodules, which seems to be characteristic of granulomas. Thin rim enhancement around the suprasellar calcifications were observed in two out of 5 patients with meningitic sequelae. Compared with CT, MR detected a few more ischemic infarcts, hemorrhagic infarcts, meningeal enhancement and granulomas in the acute meningitis group, but missed small calcifications in the basal cisterns well shown on CT in the sequelae group. Otherwise, MR generally matched CT scans. MR imaging appears to be superior to CT in evaluation of active intracranial Tb only if Gd-DTPA is used, while CT is better than MR in evaluating meningitic sequelae with calcification.

Giant subdural empyema in an infant. Sonographic observations

A giant subdural empyema was found to be the cause of a large head in a two month old female child referred for cranial sonography. The sonographic features of the subdural empyema as illustrated by this case are: (1) The presence of an extra-axial space occupying lesion with mass effect. (2) Its fluid nature with mobile echogenic debris within. (3) Its large extent from frontal to occipital region, and (4) Its thick medial echogenic wall. A total of 250 ml of pus was evacuated from the empyema and the child was doing well on follow up at four months of age.

Value of contrast enhanced CT scanning in the non-trauma emergency room patient

To determine the value of performing contrast CT in addition to non-contrast CT in the evaluation of acute non-traumatic central nervous system disorders, we retrospectively reviewed 322 cases originating from the emergency room at our institution. The most common indication for scanning was seizure activity (34% of total), followed by headache (30%), focal neurological deficit (10%), and altered mental status (8%). 75% of the non-contrast scans were normal. The contrast-enhanced scan revealed abnormalities not evident on the non-contrast scan in only three of these cases, and the information did not alter patient management. We conclude that in the acute setting, if a non-contrast CT is normal, a contrast study is usually unnecessary. Therefore, given the additional risks of contrast infusion, the contrast study, if needed, is generally best obtained at a later date, after more careful evaluation of the patient's history and medical records. If the non-contrast CT scan is abnormal, a contrast enhanced CT scan may be beneficial, but, again, is often not needed to direct acute patient management.

Intracranial tuberculoma: MR imaging

MR studies of 6 patients with intracranial tuberculoma are reviewed. All patients also underwent CT scans which showed hypo- or isodense lesions with abnormal enhancement following contrast administration. MR showed lesions with prolongation of the T1 relaxation time in every case. On the T2-weighted sequences, the signal properties of the tuberculoma varied according to the stage of evolution of the lesion. Incipient tuberculomas appeared as scattered areas of hypointensity surrounded by edema. Mature tuberculomas were composed of a dark necrotic center surrounded by an isointense capsule which was, in turn, surrounded by edema. In one patient, the center of the lesion was hyperintense probably because of liquefaction and pus formation (tuberculous abscess). While both, CT and MR, were equally sensitive in visualizing the intracranial tuberculoma in every patient, MR was slightly superior in demonstrating the extent of the lesion, especially for brainstem tuberculomas. Nevertheless, the potential role for MR diagnosis of intracranial tuberculoma is limited by the fact that other infectious or neoplasic diseases may present similar findings. The diagnosis of intracranial tuberculoma should rest on a proper integration of data from clinical manifestations, cerebrospinal fluid analysis, and neuroimaging studies.

Neuroimaging in neuro-ophthalmology

Computed tomographic scanning is an excellent modality for evaluation of most orbital and intracranial tumors and strokes. However, MR scanning is definitely superior to CT when evaluating for multiple sclerosis, posterior fossa lesions (evaluation of gaze palsies, internuclear ophthalmoplegia, and downbeat nystagmus), or when assessing an area where sagittal scanning is important (chiasmal lesions). Magnetic resonance has increased specificity when the CT is equivocal. Although MR and CT may be complementary in the information they provide, many clinical studies have shown MR to be superior to CT in evaluating cerebral infarctions, hematomas, the intracanalicular optic nerve, optic chiasm, sella turcica, and the cavernous sinus. Magnetic resonance generally has replaced metrizamide CT cisternography as the procedure of choice for evaluating the suprasellar cistern and posterior fossa. Computed tomography is still preferable for major trauma, especially involving acute fractures and hematomas, although MR is more sensitive to the more subtle intracerebral lesions, such as shear injuries and subdural hematomas, that may provide prognostic information. Computed tomography also is preferred in situations where detecting small amounts of calcification is important for the differential diagnosis. As the development of MR imaging continues with faster scan times, finer spatial resolution, the use of paramagnetic contrast agents, and with increased availability and decreased cost, MR imaging may become preferable to CT as the imaging modality of choice for the CNS and orbit.

Reversible multifocal encephalopathy following tuberculous infection

Tuberculous encephalic infection is commonly reported as confined to Asians or Africans or people living in poor hygienic conditions; very often it follows meningitis in patients with lung TB infection. We describe three western patients coming from good social environment and suffering from multifocal tuberculous encephalopathy. Two of them showed neither meningitis or lung TB when CNS involvement appeared. Complete recovery after therapy is described, together with the evolution of brain CT and, in 1 case, MRI features. The instrumental findings accompanying the complete recovery suggest that the lesions described in these cases are a localized form of encephalitis responsive to medical treatment, unlike tuberculomas, which often need surgical treatment. The occurrence of tuberculous encephalic infection in western, middle-class patients with or without meningitis emphasizes that tuberculous encephalopathy must be considered in the differential diagnosis of multifocal brain lesions.

Neurosonographic features of central nervous system infections in infancy and childhood

Infections of the central nervous system (CNS) are a serious threat to the developing brain and are a major cause of neurologic handicap in the young. Of the neuroimaging modalities available, cranial ultrasonography has become an important technique in providing information about intracranial infection because of its portability, low cost, minimal morbidity, and diagnostic image quality. Authors of recent reports described ultrasonographic changes in brain parenchyma, extracerebral fluid, and ventricles. Parenchymal changes have been observed with cerebritis, edema, hemorrhage, infarction, and abscess formation; changes in extracerebral fluid include effusion and empyema; and ventricular changes associated with ventriculitis and hydrocephalus have been reliably described. By identifying changes associated with intracranial infections, ultrasonography has emerged as a technique that provides valuable information in making the diagnosis, identifying complications, and directing decisions in management of CNS infection.

MR of childhood tuberculous meningitis

MR imaging was performed on 27 children with stage II-III tuberculous meningitis for the specific purpose of examining the brainstem, as well as comparison with other CT features of the disease. In addition to defining the ischemic disturbances of basal ganglia and diencephalon more clearly, MR also demonstrates the frequent occurrence of parenchymal signal abnormalities in the brainstem and adjacent temporal lobes, which are invisible or uncertain on CT. Although the presence of brainstem abnormalities on MR correlated well with clinical findings of brainstem dysfunction, clinical staging on admission remains the best prognostic indicator in advanced TBM. We also review the MR features of basal exudation, hydrocephalus and tuberculoma.

Magnetic resonance imaging of the brain and spine

The efficacy of magnetic resonance imaging (MRI) in the diagnosis of diseases of the central nervous system is reviewed. MRI, computed tomography (CT) and certain radionuclide studies are compared in the evaluation of intracranial tumours, cerebral vascular disease, multiple sclerosis and other white matter diseases, dementia, head injury, infection, epilepsy, spinal lesions and in paediatric central nervous system disorders. The measurement of cerebrospinal fluid volumes and dynamics by MRI is discussed. MRI most clearly has advantages where CT is degraded by bone hardening and streak artefacts (spine, skull base, posterior and temporal fossa, sella and parasellar regions) and in diseases in which the X-ray attenuation of the suspected lesion differs little from normal parenchyma (paediatric brain disorders, demyelination and dysmyelination, early oedema associated with infarction, infection or low-grade infiltrating neoplasm, subacute and chronic haemorrhage and lesions in the spinal subarachnoid space and cord). Elsewhere MRI and CT should be seen as complementary rather than competitive methods of imaging. In spite of an absence of information about the contribution of MRI to management decisions and a lack of rigorous, prospective controlled trials, MRI will play an increasing role in the diagnosis of diseases of the central nervous system.