Role of in vivo proton magnetic resonance spectroscopy in the diagnosis and management of brain abscesses

Multiparametric imaging in the evaluation of intracerebral abscesses

Cerebral abscesses are uncommon space occupying lesions; they are associated with high morbidity and mortality, though are potentially treatable. Patients often present with non-specific symptoms and may have few clinical signs. Routine clinical imaging may not give a definite diagnosis, as the findings can be indistinguishable from those of other intracranial mass lesions. We review the role of advanced MR techniques to characterise brain abscesses and discuss the role of imaging in monitoring their response to the treatment.

An unusual case report on intracranial hydatid cyst with intraventricular extension

Background

We report an interesting case of a primary isolated intraventricular and intracranial hydatid cyst in 20-year-old female that mimicked bleeding cystic tumor presenting as intraventricular hemorrhage with hydrocephalus.

Case presentation

Patient presented with headache and giddiness for 1 month. On magnetic resonance imaging, there was multiloculated multi-cystic lesion in left lateral ventricle and adjacent left periventricular deep white matter. Lesion was causing compression of the body of the left lateral ventricle with temporal horn dilatation and midline shift of 17–18 mm toward right side. On investigation, it was diagnosed intracranial hydatid cyst with intraventricular extension. Patient underwent complete removal of cerebral hydatid cyst. Follow-up postoperative computed tomography scan done which revealed no residual hydatid cyst.

Conclusion

In this case, larvae of echinococcus might have passed through capillaries of liver and lungs and entered systemic circulation reaching brain. Intracerebral hydatid cysts are rare and hence, dangerous if the diagnosis and treatment is not prompt. Intracerebral hydatid cysts have slow growth rate with late-stage symptoms, morbidity and mortality are high. So, take home message is whenever intracranial cystic lesion are found on magnetic resonance imaging hydatid cyst with possible intracranial extension should be considered in differential diagnosis.

Surgical management of choroid plexus papilloma of the cerebellopontine and cerebellomedullary angle: classification and strategy

Choroid plexus papillomas (CPPs) are primary neuroectodermal neoplasms that usually arise in the fourth ventricle in adults. In this study, we present 12 patients with CPP arising from the cerebellopontine angle (CPP-CPA) and/or of the cerebellomedullary angle (CPP-CMA) that were treated in our department. Patients who underwent surgery for the treatment for CPP-CPA/CMA from January 2004 to March 2020 were identified by a computer search of their files from the Department of Neurosurgery, Tübingen. CPPs were classified according to their location into type 1 (tumor portion only in the CPA,), type 2 (tumor portions only in the CMA), and type 3 (tumor portions both in the CPA and CMA). Patients were evaluated for initial symptoms, previous therapies in other hospitals, extent of tumor resection, recurrence rate, and complications by reviewing patient documents. Of approximately 1500 CPA lesions, which were surgically treated in our department in the last 16 years, 12 patients (mean age 42 ± 19 years) were found to have CPP-CPA/CMA. Five were male, and seven were female patients. Gross total resection was achieved in nine cases, and a subtotal resection was attained in three cases. Tumor recurrence in the same location after the first surgery in our hospital was observed in 2 patients after 15 and 40 months of follow-up, and in another patient, distant metastases (C3/4 and L3 levels) were observed. Surgical removal of CPP is the treatment of choice, but additional therapeutic options may be necessary in case of remnant tumor portions, recurrence, or malignant transformation.

MRI detection of bacterial brain abscesses and monitoring of antibiotic treatment using bacCEST

PURPOSE

To develop a new MRI method to detect and characterize brain abscesses using the CEST contrast inherently carried by bacterial cells, namely bacCEST.

METHODS

Bacteria S. aureus (ATCC #49775) and F98 and 9L glioma cells were injected stereotactically in the brains of F344 rats to form abscesses and tumors. The CEST signals of brain abscesses (n = 4) and tumors (n = 7) were acquired using 2 B1 values (i.e., 1 and 3 µT) and compared. The bacCEST signal of the brain abscesses in the rats (n = 3) receiving ampicillin (intraperitoneal injection 40 mg/kg twice daily) was acquired before, 4 and 10 days after the treatment.

RESULTS

The bacCEST signal of S. aureus was characterized in vitro as a strong and broad signal in the range of 1 to 4 ppm, with the maximum contrast occurring at 2.6 ppm. The CEST signal in S. aureus-induced brain abscesses was significantly higher than that of contralateral parenchyma (p = .003). Moreover, thanks to their different B1 independence, brain abscesses and tumors could be effectively differentiated (p = .005) using ΔCEST(2.6 ppm, 3 µT-1 µT), defined by the difference between the CEST signal (offset = 2.6 ppm) acquired using B1  = 3 µT and that of 1 µT. In treated rats, bacCEST MRI could detect the response of bacteria as early as 4 days after the antibiotic treatment (p = .035).

CONCLUSION

BacCEST MRI provides a new imaging method to detect, discriminate, and monitor bacterial infection in deep-seated organs. Because no contrast agent is needed, such an approach has a great translational potential for detecting and monitoring bacterial infection in deep-seated organs.

Magnetic Resonance Spectroscopy and its Clinical Applications: A Review

In vivo NMR spectroscopy is known as magnetic resonance spectroscopy (MRS). MRS has been applied as both a research and a clinical tool in order to detect visible or nonvisible abnormalities. The adaptability of MRS allows a technique that can probe a wide variety of metabolic uses across different tissues. Although MRS is mostly applied for brain tissue, it can be used for detection, localization, staging, tumour aggressiveness evaluation, and tumour response assessment of breast, prostate, hepatic, and other cancers. In this article, the medical applications of MRS in the brain, including tumours, neural and psychiatric disorder studies, breast, prostate, hepatic, gastrointestinal, and genitourinary investigations have been reviewed.

Intracranial hydatid cyst: imaging findings of a rare disease

Hydatid disease (echinococcosis) is a worldwide zoonosis produced by the larval stage of the Echinococcus tapeworm. The disease is endemic in many parts of the world, particularly in the Middle East, Australia, New Zealand, South America and central and south Europe. Intracranial hydatid disease is considered a rare disease and may be sometimes very difficult to diagnose based on the clinical and laboratory findings. Therefore, it is important to be aware of the condition and the imaging findings even in the non-endemic parts of the world. We report the case of a 12-year-old boy who presented with headache and vomiting for a few months. The mass was totally excised, with no postoperative complications. We present MR spectroscopy (MRS) findings in this operatively proven case of hydatid cyst of the brain. We discuss imaging findings, in particular the findings on MRS, which is rarely reported in the literature.

Sellar-Suprasellar Extraventricular Choroid Plexus Papilloma : A Case Report and Review of the Literature

Choroid plexus papillomas (CPPs) are relatively rare neuroectodermal tumors that develop from choroid plexus epithelial cells and are usually restricted to the ventricles. Extraventricular CPPs are very unusual and can be difficult to diagnose and treat. A 50-year-old male patient was admitted to our clinic complaining of headache and visual deterioration. Neurological examination found no abnormalities except decreased light perception and secondary optic atrophy in the left eye. Endocrine testing revealed normal levels of hormones produced by the pituitary and target glands. Magnetic resonance imaging of the brain revealed a huge regular-shaped lesion in the sellar-suprasellar region occupying the sella turcica and extending into the suprasellar cistern and planum sphenoidale. The lesion was completely excised by microsurgery via an ordinary left-sided pterional approach. Histopathology identified the lesion as a choroid plexus papilloma. Following the case report, literature on the origin, differential diagnosis, and treatment of this rare tumor is reviewed.

Brain Abscess in a Patient with Rendu-Osler-Weber Syndrome: Value of Proton Magnetic Resonance Spectroscopy

The diagnosis of intracranial focal lesions based on imaging studies is a challenge. In brain abscess, proton magnetic resonance spectroscopy (1H-MRS) is useful to define etiology, differentiating anaerobic from aerobic pathogens and inclusive sterile abscess based on the behavior of certain metabolites. We report a patient with Rendu-Osler-Weber syndrome, pulmonary arteriovenous fistulas, and brain abscesses characterized by brain magnetic resonance imaging (MRI), with a spectroscopy pattern compatible with anaerobic infection.

Neonatal deep white matter venous infarction and liquefaction: a pseudo-abscess lesion

BACKGROUND

Deep white matter hemorrhagic venous infarction with subsequent cavitation due to necrosis and liquefaction has been described in neonates and may be associated with infection and meningitis. In our experience, the MRI pattern of these lesions is confused with the pattern seen with cerebral abscesses.

OBJECTIVE

The purpose of our study was to characterize the MRI findings of post infarction necrosis and liquefaction after hemorrhagic deep white matter venous infarction in infants and to distinguish these lesions from cerebral abscesses.

MATERIALS AND METHODS

An institutional review board approved a retrospective review of imaging records to identify all patients with cerebral venous infarction at a children's hospital during a 10-year period. Nine infants had deep white matter hemorrhagic venous infarction with white matter fluid signal cavitary lesions. A diagnosis of cerebral abscess was considered in all. The imaging and laboratory findings in these patients are reviewed and compared to descriptions of abscesses found in the literature.

RESULTS

There were six female and three male infants. The mean age at presentation was 20 days (range: 0-90 days), while the corrected age at presentation was less than 30 days for all patients. Seven patients presented with seizures and signs of infection; one infant presented with lethargy and later proved to have protein C deficiency. MRI was performed 0-12 days from presentation in these eight patients. Another patient with known protein C deficiency underwent MRI at 30 days for follow-up of screening US abnormalities. There were a total of 38 deep cerebral white matter fluid signal cavitary lesions: 25 frontal, 9 parietal, 2 temporal, 2 occipital. Larger lesions had dependent debris. All lesions had associated hemorrhage and many lesions had evidence of adjacent small vessel venous thrombosis. Lesions imaged after gadolinium showed peripheral enhancement. Three lesions increased in size on follow-up imaging. Three patients, two with meningitis confirmed via microbiology and one with presumed meningitis by CSF counts, underwent surgical aspiration of a total of six lesions. All specimens were sent for pathology and culture and were negative for microorganisms.

CONCLUSION

Recognizing the MR appearance of cavitary necrosis and liquefaction after deep white matter cerebral venous infarction in neonates can distinguish this entity from cerebral abscess and potentially avoid an unnecessary neurosurgical aspiration procedure.

An unusual location for a choroid plexus papilloma: the pineal region

PURPOSE

Choroid plexus papillomas (CPP) are rare benign neoplasms of the central nervous system that occur most often in children during the first decade of life. They occur most often in the lateral ventricle. It is extremely rare for a CPP to occur in the pineal region. We describe the case of a child with a CPP located in the pineal region, who was initially diagnosed with obstructive hydrocephalus by cranial computed tomography (CT).

METHODS

A 9-year-old female patient presented with complaints of visual disturbance, nausea, and vomiting. Magnetic resonance imaging (MRI) showed a poor contrast-enhanced pineal-localized lesion. Anatomical variations within the patient caused her surgery to proceed using a supratentorial-occipital interhemispheric approach.

RESULTS

The tumor was totally removed, and a histological examination revealed the tumor to be a typical CPP. The patient received follow-up neurological and ophthalmologic examinations at 3, 6, 9, 12, 24, and 36 months postoperatively, which demonstrated her progressive improvement.

CONCLUSIONS

CPPs may have a wide range of locations and resulting symptoms. However, the pineal region is a rarely encountered location, particularly for pediatric patients. It is of great value to correctly differentiate neoplasms such as germ cell tumors, pineocytomas, meningiomas, and astrocytomas, so that patients receive the correct diagnosis and treatment approach.

Noninvasive imaging of infection after treatment with tumor-homing bacteria using Chemical Exchange Saturation Transfer (CEST) MRI

PURPOSE

To develop a noninvasive MRI method for determining the germination and infection of tumor-homing bacteria in bacteriolytic cancer therapy using endogenous CEST contrast.

METHODS

The CEST parameters of the anaerobic gram-positive bacterium Clostridium novyi-NT (C. novyi-NT) were first characterized in vitro, then used to detect C. novyi-NT germination and infection in subcutaneous CT26 colorectal tumor-bearing mice (n = 6) after injection of 300 million bacterial spores. Lipopolysacharide (LPS) injected mice were used to exclude that the changes of CEST MRI were due to inflammation.

RESULTS

CEST contrast was observed over a broad frequency range for bacterial suspensions in vitro, with the maximum contrast around 2.6 ppm from the water resonance. No signal could be detected for bacterial spores, demonstrating the specificity for germination. In vivo, a significant elevation of CEST contrast was identified in C. novyi-NT infected tumors as compared to those before bacterial germination and infection (P < 0.05; n = 6). No significant change was observed in tumors with LPS-induced sterile inflammation (P > 0.05; n = 4).

CONCLUSION

Endogenous bacterial CEST contrast (bacCEST) can be used to monitor the germination and proliferation of the therapeutic bacterium C. novyi-NT without a need for exogenous cell labeling probes.

Proton MR spectroscopy in patients with pyogenic brain abscess: MR spectroscopic imaging versus single-voxel spectroscopy

PURPOSE

Single-voxel spectroscopy (SVS) has been the gold standard technique to diagnose the pyogenic abssess. Two-dimensional magnetic resonance spectroscopic imaging (MRSI) is able to provide spatial distribution of metabolic concentration, and is potentially more suitable for differential diagnosis between abscess and necrotic tumors. Therefore, the purpose of this study was to evaluate the equivalence of MRSI and SVS in the detection of the metabolites in pyogenic brain abscesses.

MATERIALS AND METHODS

Forty-two patients with pyogenic abscesses were studied by using both SVS and MRSI methods. Two neuroradiologists reviewed the MRS data independently. A κ value was calculated to express inter-reader agreement of the abscesses metabolites, and a correlation coefficient was calculated to show the similarity of two spectra. After consensus judgment of two readers, the binary value of metabolites of pyogenic abscesses (presence or absence) was compared between SVS and MRSI.

RESULTS

The consistency of spectral interpretation of the two readers was very good (κ ranged from 0.95 to 1), and the similarity of two spectra was also very high (cc=0.9±0.05). After consensus judgment of two readers, the sensitivities of MRSI ranged from 91% (acetate) to 100% (amino acids, succinate, lactate, lipid), and the specificities of MRSI were 100% for detecting all metabolites with SVS as reference.

CONCLUSION

SVS and MRSI provide similar metabolites in the cavity of pyogenic brain abscess. With additional metabolic information of cavity wall and contralateral normal-appearing brain tissue, MRSI would be a more suitable technique to differentiate abscesses from necrotic tumors.

Magnetic resonance spectroscopy findings of pyogenic, tuberculous, and Cryptococcus intracranial abscesses

Proton magnetic resonance spectroscopy (MRS) complements conventional methods used to differentiate intracranial cystic lesions. We report MRS findings of three cases that were diagnosed as pyogenic, tuberculous, and Cryptococcus abscesses before instituting any medical or surgical therapy. The pyogenic brain abscess had typical specific spectral findings (i.e., the demonstration of amino acids). Lactate and lipid peaks were visible in the tuberculous abscess. Cryptococcus neoformans can appear differently in different brain regions, which may lead to different spectral findings.

MRS findings in cerebral coenurosis due to Taenia multiceps

Cerebral coenurosis due to Taenia multiceps is a rare infection with no case reports from India. A 55-year-old male patient had presented with progressive symptoms of hemiparesis of 1-year duration. Magnetic resonance imaging (MRI) with magnetic resonance spectroscopy (MRS) of the lesion was performed that showed a septated cystic lesion in left parieto-occipital lobe. Multivoxel MRS through the lesion was performed using repetition time of 1500 ms and time to echo of 144 ms at 3T MRI. MRS showed mildly elevated choline (Cho), depressed creatine (Cr), and N-acetyl aspartate (NAA), a large peak of lactate, pyruvate, and acetate peaks. To best of our knowledge, there has been no reported case of in vivo proton MRS finding ever reported. We present MRS findings in this operatively proven case of T. multiceps cyst of the brain.

Primary choroid plexus papilloma in the pituitary fossa: case report and literature review

Choroid plexus papillomas are rare tumors of the central nervous system and are usually confined to the ventricular system. We illustrated a primary choroid plexus papilloma in the pituitary fossa. A 31-year-old female presented with amenorrhea and intermittent galactorrhoea, with no visual complaints in the last 2 years. Endocrine testing showed no hormone excess or deficiency of the pituitary and target glands, except for a higher prolactin level (56 ng/ml). A sharply circumscribed regular mass in the sellar region occupying the entire sella turcica and extending into the suprasellar cistern was demonstrated on MR imaging with gadolinium diethylenetriamine pentaacetic acid. The patient underwent an endonasal trans-sphenoidal approach. Complete microsurgical excision and complete preservation of the normal pituitary gland was achieved, with normal prolactin level. The histopathology showed that the lesion was a choroid plexus papilloma. Theories of the origin, the differential diagnosis, and treatment of the rare tumor are discussed.

Utility of in vitro proton magnetic resonance spectroscopy in aetiological characterisation of brain abscesses

PURPOSE

Brain abscesses often present an aetiological dilemma. Microscopy is insensitive and culture techniques are time consuming. Hence, a new rapid technique in vitro Proton Magnetic Resonance Spectroscopy (1HMRS) was evaluated for its usefulness in the identification of aetiology of brain abscesses.

MATERIALS AND METHODS

A total of 39 pus specimens from brain abscesses were subjected to in vitro 1HMRS. These pus specimens were also processed by conventional culture methods. The spectral patterns generated by in vitro 1HMRS were further correlated with culture results.

RESULTS

Pus specimens which showed the presence of anaerobes on culture revealed the presence of multiplet at 0.9 ppm (100%), lactate-lipid at 1.3 ppm (100%), acetate at 1.92 ppm (100%) and succinate at 2.4 ppm (75%). Pus specimens that revealed the presence of facultative anaerobes on culture showed a pattern B, i.e., the presence of lactate-lipid at 1.3 ppm (100%), acetate at 1.92 ppm (88.88%) along with the multiplet at 0.9 ppm (100%). Pattern C was seen in aerobic infection which showed the presence of lactate-lipid at 1.3 ppm (100%) along with the multiplet at 0.9 ppm. Pus from two tuberculous abscesses showed the complete absence of multiplet at 0.9 ppm.

CONCLUSIONS

We observed in this study that it was possible to differentiate bacterial and tuberculous brain abscesses using in vitro 1HMRS. Further, it was also possible to distinguish between aerobic and anaerobic brain abscesses on the basis of spectral patterns. In vitro 1HMRS of fungal and actinomycotic brain abscess are also presented for its unusual spectra.

[Value of MR spectroscopy in infectious and inflammatory brain diseases]

Proton magnetic resonance spectroscopy (MRS) is a non-invasive method for measuring cerebral metabolite concentrations in various pathologic conditions. This review discusses the MRS findings in the most common infectious and inflammatory brain diseases.

Choroid plexus papilloma originating in the sella turcica--case report

A 51-year-old female presented with a rare case of choroid plexus papilloma originating in the sella turcica manifesting as headaches that was not readily distinguishable preoperatively from pituitary adenoma. Head magnetic resonance imaging revealed a tumor extending from the sella turcica to the suprasellar cistern. The tumor was removed via an endonasal transsphenoidal approach. Histological examination indicated a papillary structure covered with a layer of columnar epithelial cells that resembled normal choroid plexus. These findings, together with immunohistochemistry, led to a diagnosis of choroid plexus papilloma.

Ectopic choroid plexus associated with trigeminal neuralgia: case report

INTRODUCTION

A 55-year-old man underwent a microvascular decompression procedure for a pharmacoresistant trigeminal neuralgia. Preoperative MRI showed a neurovascular conflict between the Vth nerve root and the superior cerebellar artery.

METHODS

Dissection of the intracisternal trigeminal root was undertaken, and a piece of Teflon was positioned between the artery and the nerve.

RESULTS

Choroid plexus was found squeezing the root entry zone of the Vth nerve and partially removed. The patient did not improve after the vascular decompression procedure. Trigeminal neuralgia could be due to a mechanical irritation of the intracisternal nerve root.

CONCLUSION

Since vascular decompression of the trigeminal root did not relieve the pain, we suggest that the presence of choroid plexus at the root entry zone of the nerve may have induced trigeminal neuralgia in this patient.

In vivo proton MR spectroscopy evaluation of pyogenic brain abscesses: a report of 194 cases

BACKGROUND AND PURPOSE

The combination of nonspecific clinical findings and similarities in morphologic appearances on imaging often makes it difficult to distinguish abscesses from other brain lesions. We present a retrospective analysis of in vivo (1)H-MR spectroscopy data for characterization of the etiology of the brain abscess based on the established criteria and demonstrate the sensitivity and specificity of metabolite markers assigned to specific bacterial groups defined by the microbial culture in 194 patients.

MATERIALS AND METHODS

Conventional MR imaging and in vivo (1)H-MR spectroscopy data were evaluated from patients with pyogenic brain abscesses, with ages ranging from 3 to 60 years. Imaging and (1)H-MR spectroscopy were performed on a 1.5T scanner. After MR imaging was performed and analyzed, pus aspirates were obtained in all patients. The causative organisms were confirmed by pus cultures.

RESULTS

Resonance of AAs with or without other metabolites on in vivo (1)H-MR spectroscopy was observed in 80% of abscesses, with a sensitivity and specificity of 0.72 and 0.30, respectively. Most obligate anaerobes and some facultative anaerobes showed the presence of Lac/Lip, AAs, and Ac with or without Suc. Mostly obligate aerobes or facultative anaerobes showed the presence of Lac and AAs, with or without lipids.

CONCLUSIONS

The presence of AAs on in vivo (1)H-MR spectroscopy is a sensitive marker of pyogenic abscess, but its absence does not rule out a pyogenic etiology. The presence of Ac with or without Suc favors an anaerobic bacterial origin of the abscess; however, this may also be seen in some of the abscesses secondary to facultative anaerobes.

Distinction between pyogenic brain abscess and necrotic brain tumour using 3-tesla MR spectroscopy, diffusion and perfusion imaging

The purpose of this study is to compare the effectiveness of relative cerebral blood volume, apparent diffusion coefficient and spectroscopic imaging in differentiating between cerebral abscesses and necrotic tumours. In the prospective study, a 3-tesla MR unit was used to perform proton MR spectroscopy, diffusion and perfusion imaging in 20 patients with cerebral abscesses and 26 patients who had solitary brain tumours (14 high-grade gliomas and 12 metastases). We found the mean apparent diffusion coefficient value at the central cavities of the cerebral abscesses to be significantly lower than in necrotic tumours. The mean relative cerebral blood volume values of the necrotic tumour wall were statistically significantly higher than the mean relative cerebral blood volume values of the cerebral abscess wall by the Student's t-test. The proton spectra obtained revealed amino acids only in the cerebral abscesses. Although the conventional MRI characteristics of cerebral abscesses and necrotic tumours may sometimes be similar, diffusion, perfusion-weighted and spectroscopic MRI enables distinction between the two.

[Magnetic resonance spectroscopy for inflammatory brain diseases]

Magnetic resonance spectroscopy (MRS) is a non-invasive method for investigation of cerebral metabolite concentrations in various pathologic conditions. The clinical use of MRS for intracranial disorders is well established. In this review the characteristic MRS findings for the most important inflammatory brain diseases will be discussed.

In vivo differentiation of aerobic brain abscesses and necrotic glioblastomas multiforme using proton MR spectroscopic imaging

BACKGROUND AND PURPOSE

Abscesses caused by aerobic bacteria (aerobic abscesses) can simulate intracranial glioblastomas multiforme (GBMs) in MR imaging appearance and single voxel (SV) proton MR spectroscopy of the central cavity. The purpose of our study was to determine whether MR spectroscopic imaging (SI) can be used to differentiate aerobic abscesses from GBMs. Our hypothesis was that metabolite levels of choline (Cho) are decreased in the ring-enhancing portion of abscesses compared with GBMs.

MATERIALS AND METHODS

Fifteen patients with aerobic abscesses were studied on a 1.5T MR scanner using an SV method and an SI method. Proton MR spectra of 15 GBMs with similar conventional MR imaging appearances were used for comparison. The resonance peaks in the cavity, including lactate, cytosolic amino acids, acetate, succinate, and lipids, were analyzed by both SV MR spectroscopy and MRSI. In the contrast-enhancing rim of each lesion, peak areas of N-acetylaspartate (NAA), choline (Cho), lipid and lactate (LL), and creatine (Cr) were measured by MRSI. The peak areas of NAA-n, Cho-n, and Cr-n in the corresponding contralateral normal-appearing (-n) brain were also measured. Maximum Cho/Cr, Cho/NAA, LL/Cr-n, and Cho/Cho-n and minimum Cr/Cr-n and NAA/NAA-n ratios in abscesses and GBMs were compared using the Wilcoxon rank sum test. After receiver operating characteristic curve analysis, diagnostic accuracy was compared.

RESULTS

Cytosolic amino acid peaks were found in the cavity in 7 of 15 patients with aerobic abscesses. Means and SDs of maximum Cho/Cr, Cho/NAA, LL/Cr-n, and Cho/Cho-n and minimum Cr/Cr-n and NAA/NAA-n ratios were 3.38 +/- 1.09, 3.88 +/- 2.13, 2.72 +/- 1.45, 1.98 +/- 0.53, 0.53 +/- 0.16, and 0.44 +/- 0.09, respectively, in the GBMs, and 1.77 +/- 0.49, 1.48 +/- 0.51, 2.11 +/- 0.67, 0.81 +/- 0.21, 0.48 +/- 0.2, and 0.5 +/- 0.15, respectively, in the abscesses. Significant differences were found in the maximum Cho/Cr (P = .001), Cho/NAA (P = .006), and Cho/Cho-n ratios (P < .001) between abscesses and GBMs. Diagnostic accuracy was higher by Cho/Cho-n ratio than Cho/Cr and Cho/NAA ratios (93.3% versus 86.7% and 76.7%).

CONCLUSION

Metabolite ratios and maximum Cho/Cho-n, Cho/Cr, and Cho/NAA ratios of the contrast-enhancing rim were significantly different and useful in differentiating aerobic abscesses from GBMs by MRSI.

The role of proton magnetic resonance spectroscopy in the diagnosis and categorization of cerebral abscesses

✓ Despite recent advances in neuroimaging, differentiation between cerebral abscesses and necrotic tumors with ring-type contrast enhancement can be puzzling at times. The introduction of advanced imaging techniques, such as diffusion-weighted imaging, has contributed to the identification of cerebral abscesses. However, differentiation may be impossible with imaging only. In this review the authors evaluate the role of proton magnetic resonance (MR) spectroscopy in differentiating between cerebral abscesses and necrotic tumors and address the spectral characteristics of intracranial abscesses. A large number of metabolites not detected in the normal brain spectra may be detected and give valuable information regarding the nature of the abscesses. Proton MR spectroscopy is a safe, noninvasive diagnostic modality, which could significantly increase the accuracy and specificity of conventional MR imaging in differentiating between malignant tumors and cerebral abscesses and provide valuable information regarding the cause of an abscess, as well as, its response to the chosen treatment.

(1)H MR spectroscopy of inflammation, infection and ischemia of the brain

Different pathologic patterns in multiple sclerosis (MS) are reflected by alterations of metabolites in (1)H MR spectroscopy of the brain. Elevated choline (Cho), lactate (Lac), lipids and macromolecules are reliable markers for acute demyelination regardless of the clinical entity (also in acute disseminated encephalomyelitis). N-acetyl-aspartate (NAA) is a suitable marker for neuronal integrity. It is reduced in acute MS lesions and in normal appearing white matter, even distant to acute and chronic-lesions. Recovery from reduced NAA levels to subnormal values during remyelination, and varying time courses of NAA in normal appearing white matter during relapsing remitting disease indicate the value of this spectroscopic marker for monitoring activity and recovery. Inositol (Ins) is increased in chronic MS lesions being a marker for astrocytic gliosis. In viral disease, Cho and Ins are always increased, whereas a reduction of NAA mostly reflects an advanced or a detoriated clinical state. In bacterial brain abscesses, numerous amino acids, lipids and Lac can be elevated. In ischemia, especially the Lac/NAA in comparison with perfusion and diffusion weighted imaging seems to be a new measure for areas of metabolic need, and may help to better characterise the penumbra of the stroke and the final infarct size.

Primary choroid plexus papilloma of the sellar region

BACKGROUND

Choroid plexus papillomas are rare tumors of the central nervous system and are usually confined to the ventricle system. We describe a choroid plexus papilloma located in the sella turcica that was identified pathologically.

CASE DESCRIPTION

A 49-year-old woman with a 5-year history of progressive visual deterioration in the left eye was admitted to our hospital. Neurological examination found no abnormality except for the perception of light and secondary optic atrophy in her left eye. Careful endocrine testing did not show any hormone excess or deficiency of the pituitary and target glands. Magnetic resonance imaging demonstrated a hemorrhagic mass in the sellar region, which occupied the entire sella turcica and extended to the suprasellar cistern. The mass was excised via an endonasal trans-sphenoidal approach. Histologic examination proved that the lesion was a choroid plexus papilloma.

CONCLUSION

Choroid plexus papillomas arising in and occupying the sella are rare, although some radiographic patterns of ectopic choroid plexus papillomas have been reported. A review of the current literature revealed no similar cases of a choroid plexus papilloma. We discuss the different radiological appearances of choroid plexus papillomas, the differential diagnosis, and treatment.

Proton magnetic resonance spectroscopy and diffusion-weighted imaging in intracranial cystic mass lesions

BACKGROUND

The differential diagnosis of various intracranial cystic lesions is sometimes difficult on the basis of CT or MRI findings. Our objective was to evaluate (1)H MRS and DWI in the differential diagnosis of these lesions and in comparison with conventional MRI.

METHODS

Fifty patients with intracranial cystic lesions (21 pyogenic abscesses, 23 tumor cysts, 3 epidermoid cysts, and 3 arachnoid cysts) were evaluated with conventional MRI, DWI, and in vivo (1)H MRS. Preoperative diagnosis of the lesions was based on the results of DWI and in vivo MRS. All DWI and (1)H MRS studies were performed with a clinical 1.5-T system. The DWI was performed using single-shot spin-echo echo-planar pulse sequence with b = 1000 s/mm(2). The ADC value was measured. Diagnostic accuracy of conventional MRI, DWI, and in vivo (1)H MRS was calculated with respect to a final diagnosis of brain abscess vs nonabscess cystic tumor.

RESULTS

Lactate and cytosolic amino acids with/without succinate, acetate, and alanine were observed in 18 of 21 cases of abscesses on MRS. In 3 cases of epidermoid cysts, lactate was observed and could be differentiated from 3 cases of arachnoid cysts, which showed only minimal lactate. Only lactate was seen in 14 of 23 patients with tumor cysts, whereas both lipid/lactate and choline were visible in 9 patients with tumor cysts. Increased signal was seen in 20 of 21 patients with abscesses and 3 patients with epidermoid cysts on DWI. Decreased signal was observed in 22 of 23 patients with tumor cysts and 3 patients with arachnoid cyst on DWI. Diagnostic accuracy, sensitivity, specificity, positive predictive value, and negative predictive value of conventional MRI for the differentiation of brain abscess from nonabscess cystic tumor were 61.4%, 61.9%, 60.9%, 59.1%, and 63.6%, respectively, whereas they were 93.2%, 85.7%, 100%, 100%, and 88.5% with MRS; 95.5%, 95.2%, 95.7%, 95.2%, and 95.7% with DWI; and 97.7%, 95.2%, 100%, 100%, and 95.8% with MRS and DWI. Magnetic resonance imaging, when combined with in vivo MRS and DWI, accurately predicted the diagnosis in 47 (94%) of 50 and 48 (96%) of 50 of the cases, respectively.

CONCLUSIONS

Proton MRS and DWI are useful as additional diagnostic modalities in differentiating intracranial cystic lesions. Combination of DWI with calculated ADC values and metabolite spectrum acquired by MRS add more information to MRI in the differentiation of intracranial cystic mass lesions.

Imaging of cerebellopontine angle lesions: an update. Part 2: intra-axial lesions, skull base lesions that may invade the CPA region, and non-enhancing extra-axial lesions

Computed tomography (CT) and magnetic resonance (MR) imaging reliably demonstrate typical features of vestibular schwannomas or meningiomas in the vast majority of mass lesions responsible for cerebellopontine angle (CPA) syndrome. However, a large variety of unusual lesions can also be encountered in the CPA. Covering the entire spectrum of lesions potentially found in the CPA, these articles explain the pertinent neuroimaging features that radiologists need to know to make clinically relevant diagnoses in these cases, including data from diffusion- and perfusion-weighted imaging or MR spectroscopy, when available. A diagnostic algorithm based on the lesion's site of origin, shape and margins, density, signal intensity and contrast material uptake is also proposed. Non-enhancing extra-axial CPA masses are cystic (epidermoid cyst, arachnoid cyst, neurenteric cyst) or contain fat (dermoid cyst, lipoma). Tumours can also extend into the CPA by extension from the skull base (paraganglioma, chondromatous tumours, chordoma, cholesterol granuloma, endolymphatic sac tumour). Finally, brain stem or ventricular tumours can present with a significant exophytic component in the CPA that may be difficult to differentiate from an extra-axial lesion (lymphoma, hemangioblastoma, choroid plexus papilloma, ependymoma, glioma, medulloblastoma, dysembryoplastic neuroepithelial tumour).

Assessment of inhibitory potency of antibiotics by MRI: apparent T2 as a marker of cell growth

A new method to assess the antibiotic potency by MRI has been developed. Correlating 1H NMR spectra of bacterial cultures with the extracellular parameters T2, OD600, and pH, a relationship between cell growth and T2 variations was established. T2 is influenced by chemical exchange that depends on pH, composition, and concentration of the medium. Changes in the medium from bacterial metabolism are reflected in alternating T2 values. At 17.6 T, growth curves based on T2 values were measured simultaneously of several cultures of Streptococcus vestibularis. From T2 growth curves in the presence of varying concentrations of vancomycin, the minimum inhibitory concentration of the antibiotic could be determined to be 0.33+/-0.08 microM. This value was in good agreement with the result obtained by the conventional broth microdilution. In principle, T2 growth curves can be determined on a large number of cultures simultaneously and may potentially be used as a novel tool in high through-put screening of novel anti-infective substances.

Identification of diffuse and focal brain lesions by clinical magnetic resonance spectroscopy

The purpose of this paper is to facilitate the comparison of magnetic resonance (MR) spectra acquired from unknown brain lesions with published spectra in order to help identify unknown lesions in clinical settings. The paper includes lists of references for published MR spectra of various brain diseases, including pyogenic abscesses, encephalitis (herpes simplex, Rasmussen's and subacute sclerosing panencephalitis), neurocysticercosis, tuberculoma, cysts (arachnoid, epidermoid and hydatid), acute disseminated encephalomyelitis (ADEM), adrenoleukodystrophy (ALD), Alexander disease, Canavan's disease, Krabbe disease (globoid cell leukodystrophy), Leigh's disease, megalencephalic leukoencephalopathy with cysts, metachromatic leukodystrophy (MLD), Pelizaeus-Merzbacher disease, Zellweger syndrome, HIV-associated lesions [cryptococcus, lymphoma, toxoplasmosis and progressive multifocal leukoencephalopathy (PML)], hydrocephalus and tuberous sclerosis. Each list includes information on the echo time(s) (TE) of the published spectra, whether a control spectrum is shown, whether the corresponding image and voxel position are shown and the patient ages if known. The references are listed in the approximate order of usefulness, based on spectral quality, number of spectra, range of echo times and whether the voxel positions are shown. Spectra of Zellweger syndrome, cryptococcal infection, toxoplasmosis and lymphoma are included, along with a spectrum showing propanediol (propylene glycol).

Proton MR spectroscopy of the brain with a focus on chemical issues

Among the vast number of metabolites in living tissues, metabolites detectable by in vivo MR spectroscopy are limited to those present in high concentrations, and the actual number is only 10 to 20. None is disease-specific. Interpretation of MRS data, therefore, must be based on general knowledge of biochemical processes in association with pathological changes. Each spectrum is a window on the actual biochemical changes taking place within the living tissues, but the reality entails a wide and confusing variance. Continuous expansion of the knowledge may reduce the uncertainty of interpreting MRS data.

Identification ofStaphylococcus aureusBrain Abscesses: Rat and Human Studies with1H MR Spectroscopy

PURPOSE

To determine the feasibility of a statistical classification strategy (SCS) and the identity of metabolites of bacterial and host origins that potentially contributed to the most discriminatory regions of magnetic resonance (MR) spectra from Staphylococcus aureus abscesses of biopsy material from controls, gliomas, and staphylococcal abscesses.

MATERIALS AND METHODS

Human and animal study received ethics committee approval, and informed patient consent was obtained. A rat model of S aureus brain abscess was developed. Histologic and microbiologic examination was performed to assess abscess development 3-4, 6-8, and 10-15 days after initiation. Metabolite profiles in pus (n = 62) and controls (n = 37) were characterized with ex vivo MR spectroscopy and compared with data from rat gliomas (n = 27). SCS, optimal region selection, and development of pairwise classifiers allowed MR spectra of abscesses (n = 42, day 6-8) to be distinguished from those of glioblastoma multiforme and controls. MR spectroscopy profiles of pus from animal abscesses were compared with in vivo MR spectra from patients with staphylococcal brain abscesses (n = 7, aged 6-67 years) and ex vivo pus MR spectra from patients with S aureus abscesses.

RESULTS

Histologically confirmed abscesses were present 6-8 days after stereotactic injection of S aureus in 42 of 47 rats (89%). MR spectra of abscesses and glioblastoma multiforme in the animal model were similar. Typical metabolites of abscesses due to anaerobe bacteria (acetate, succinate, amino acids) were not detectable in S aureus abscesses in rats or humans. MR spectroscopic findings from controls, abscesses, and gliomas were distinguished by means of SCS with an accuracy of 99%. Analysis of the most discriminatory regions with two-dimensional correlation spectra indicated that glutamine and/or glutamate and aspartate potentially contributed to successful classification.

CONCLUSION

S aureus is detectable in abscesses with a non-culture-based method in an animal model.

MR spectroscopy of brain tumors

MR Spectroscopy provides a means to characterize the metabolite profiles of tumoral and non-tumoral lesions in the brain. This article aims to provide tools to increase our sensitivity and specificity of neurodiagnosis, particularly in combination with other advanced MRI techniques such as perfusion MR imaging.

Effect of Gamma-Hydroxybutyric Acid on Lipid Peroxidation and Tissue Lactate Level in Experimental Head Trauma

BACKGROUND

This study was designed to determine the effects of gamma-hydroxybutyric acid (GHB) on tissue lactate and malondialdehyde (MDA) levels in rabbit brain after experimental head trauma.

METHODS

Thirty New Zealand rabbits were divided equally into three groups: group S was the sham-operated group, group C, and group GHB received head trauma, where group C was the untreated and group GHB was the treated group. Head trauma was delivered by performing a craniectomy over the right hemisphere and dropping a weight of 10 g from a height of 80 cm. GHB was administered 400 mg/kg intravenously for 10 minutes after the head trauma to group GHB. The nontraumatized side was named "1" and the traumatized side was named "2." One hour after trauma, brain cortices were resected from both sides and the concentrations of lactate and MDA were determined.

RESULTS

There were significant differences between lactate and MDA levels of group S and all other groups (C1, C2, GHB1, and GHB2) except between lactate levels of group S and group GHB1, the nontraumatized and traumatized sides of groups C and group GHB, group C2 versus group GHB2, and group C1 versus group GHB1 (p < 0.05). Rectal temperature after the administration of GHB in group GHB was found lower than in groups S and C (p < 0.05).

CONCLUSION

These results demonstrate that head trauma leads to an increase in brain tissue lactate and MDA levels, and GHB effectively suppresses the increase of lactate and MDA.

Higher succinate than acetate levels differentiate cerebral degenerating cysticerci from anaerobic abscesses on in-vivo proton MR spectroscopy

We present three patients with large intraparenchymal isolated degenerating cysticerci in whom the diagnosis was primarily based on in-vivo proton MR spectroscopy, and subsequently confirmed histologically. We suggest that the presence of succinate alone or more succinate acetate indicates the presence of degenerating cysticerci and differentiates them from anaerobic brain abscesses, which show acetate alone or in higher concentration than succinate, even when the clinical and imaging features are similar.

Brain Abscesses: Etiologic Categorization with in Vivo Proton MR Spectroscopy

PURPOSE

To compare the metabolite patterns observed at in vivo proton magnetic resonance (MR) spectroscopy of brain abscesses in patients for whom bacteriologic information was obtained from cultures and to categorize the MR spectral patterns with respect to the underlying etiologic agents.

MATERIALS AND METHODS

MR imaging and in vivo single-voxel proton MR spectroscopic data obtained from 75 patients with brain abscesses were retrospectively analyzed. Ex vivo spectroscopic experiments with the pus from 45 of these patients also were performed, and the data were further categorized on the basis of bacteriologic information. Quantification of various metabolites and metabolite ratios and statistical analyses of lactate and lactate/amino acid (AA) ratio levels were performed by using one-way analysis of variance.

RESULTS

On the basis of in vivo proton MR spectroscopic and bacteriologic analysis findings, data were classified into three categories: Group 1 data showed resonances of lactate, AAs, and acetate, with or without succinate at proton MR spectroscopy; cultures for this group showed obligate anaerobes or a mixture of obligate and facultative anaerobes. The metabolite patterns in the group 2 and group 3 data were similar to the pattern of the group 1 data, with the exception that acetate and succinate resonances were absent. Culture was positive for either obligate aerobes or facultative anaerobes in group 2 and was sterile in group 3. At analysis of variance, in vivo data showed significant differences in lactate/AA ratios (P =.008), and ex vivo data showed significant differences in lactate levels (P =.001) among the three groups.

CONCLUSION

It is possible to differentiate anaerobic from aerobic or sterile brain abscesses on the basis of metabolite patterns observed at in vivo proton MR spectroscopy. This information may be useful in facilitating prompt and appropriate treatment of patients with these abscesses.

Proton magnetic resonance spectroscopy as a potential tool for differentiating between abdominal fluid collections

PURPOSE

To determine the utility of proton magnetic resonance spectroscopy (MRS) in distinguishing abdominal fluid types.

MATERIALS AND METHODS

Abdominal fluid samples were obtained from patients undergoing therapeutic percutaneous drainage. In vitro spectroscopy was performed using a 1.5-T scanner and a head coil. Single voxel spectra were obtained using a point resolved spin-echo sequence with water suppression (TR/TE 2000 msec/35 msec). The peak pattern for each sample was examined and the signal-to-noise ratio (SNR) estimated (ratio of tallest peak to noise at <0 ppm).

RESULTS

Thirty-five samples were analyzed: purulent collection (eight), serosanguinous collection (eight), non-chylous ascites (six), chylous ascites (one), bile (seven), and bile with iodinated contrast media (five). The mean SNR of the dominant peak was: purulent collection, 12.7; serosanguinous collection, 3.2; non-chylous ascites, 2.4; chylous ascites, 8.8; bile, 1.4; and bile with contrast media, 60.8. Pus samples had a broad based peak pattern with continuous signal of >1.5 ppm width situated within the range 0.2-2.5 ppm, not found in other samples. Chylous ascites (one sample) had a distinctive peak at 1.2 ppm. Bile with contrast had three peaks at 3.5/3.6, 2.6, and 2.1 ppm. No other patterns were found to be discriminatory. Common non-specific patterns seen included a bifid peak at 1.1-1.3 ppm and a broad based peak situated between 3 and 4 ppm.

CONCLUSIONS

The H1 spectra of purulent fluid has a higher SNR than common non-purulent abdominal fluids and a distinct broad based peak pattern from 0.2-2.5 ppm. Proton spectroscopy may be a useful tool for distinguishing purulent from non-purulent intra-abdominal collections.

Broad identification of bacterial type from pus by 1H MR spectroscopy

BACKGROUND

Abscess formation is a common bacterial infection and requires an immediate antimicrobial approach for apposite treatment. Delay in patient treatment is usually a common feature, as the bacterial identification of clinical samples is based on the culture, which is a time-consuming exercise. The current study was aimed at developing an alternative technique with the potential for rapid bacterial group identification.

MATERIALS AND METHODS

In the present study we performed ex vivo proton magnetic resonance spectroscopy of 40 pus samples collected from abscesses in different locations and the results have been retrospectively compared with the microorganism identified in the pus culture. In addition, the microbes obtained from the culture have been further subcultured and studied with magnetic resonance spectroscopy to identify the bacterial fingerprint in the pus sample seen on spectroscopy.

RESULTS

On reviewing the spectra obtained from the various abscesses, they were found to be qualitatively similar for a particular bacterium. The similar spectral pattern of the pus with obligate aerobes/anaerobes and pure cultures of the same bacteria suggests its strict metabolism under in vivo and in vitro conditions, respectively.

CONCLUSIONS

The characteristic metabolite pattern of obligate anaerobes may be used as a prototype for its rapid identification. This information may be of value for more appropriate clinical management of such cases.

[Brain abscesses after extracranial infections of the head and neck area]

The authors report on 20 immunocompetent patients with brain abscess after 12 cases of middle ear, seven tooth and a single frontal sinus infection. The clinical aspects, hematochemical and microbiological data, the role of imaging diagnostics (CT, MR) and the type of treatment are analysed. Neurosurgery was performed on 17 patients (85%), eight of whom subsequently underwent evacuation of the primary source of infection (four mastoidectomies, two timpanoplasties, two tooth extractions). Mastoidectomy was eventually carried out on one of the three patients who did not undergo neurosurgery. Microbiological diagnosis was possible in nine patients through culture examination: Proteus mirabilis in three cases, Peptostreptococcus sp. in two, Micrococcus varians, Proteus vulgaris, Streptococcus sanguis and Streptococcus viridans not typed in single cases. The pus was sterile in eight patients (47.1% of those operated). An association of two antimicrobial agents was used in 18 patients, while in two cases monotherapy was preferred, based on the isolated bacteria. Treatment lasted on average 38 days. The most frequently used therapy regimen (75%) was the association of a beta-lactam drug with chloramphenicol or metronidazole. Therapy was successful in 19/20 patients; one patient died. There was no significant difference in prognostic terms with regard to sex, age, duration of symptoms prior to diagnosis, clinical picture at onset, number and size of abscesses or type of treatment. Recognising the first clinical signs and symptoms (headache, fever, alterations in consciousness, focal neurological deficit, epileptic seizures) is extremely important for prompt diagnosis of brain abscess.

Proton MR spectroscopy and diffusion-weighted MR imaging for the diagnosis of intracranial tuberculomas. Report of two cases

With the current prevalence of tuberculosis, the incidence of intracranial tuberculoma may be on the rise in industrialized nations. However, clinical findings suggestive of systemic tuberculosis are frequently subtle or absent in patients with intracranial tuberculoma, and no specific neuroradiologic characteristics of tuberculoma have been defined as yet. We report two cases of ring-enhanced intracranial tuberculoma in which magnetic resonance (MR) proton spectroscopy and diffusion-weighted (DW) imaging were useful in the differential diagnosis between tuberculoma and other ring-enhanced mass lesions. Pulmonary tuberculosis had been diagnosed in one patient, but radiologic lung study and tuberculin skin test were negative in the other. DW imaging showed bright signal intensity in the core of all lesions in both patients. Malignant gliomas and metastatic brain tumors do not have this characteristic. Proton MR spectroscopy of lesion cores showed lipid peaks and a choline peak in one, and a lipid/lactate mixture pattern in the other, which differed distinctively from those of the pyogenic brain abscess. in each case, one lesion was surgically removed. Antituberculosis drugs were started before surgery for one patient and after surgery for the other. In both, the remaining lesions were reduced significantly in size. We discuss the diagnostic potential of these MR techniques and management options of intracranial tuberculoma.

Unusual case of extradural choroid plexus papilloma of the sacral canal. Case report

An unusual case of a sacral, extradural choroid plexus papilloma involving the S1-3 level is described. This 50-year-old woman presented with a 4-month history of pain involving her right buttock, perineum, and leg. Contrast-enhanced magnetic resonance (MR) imaging of the spine revealed a well-defined, mildly enhancing sacral canal mass at the S1-3 level; its appearance was consistent with that of a benign tumor. Intraoperatively, the lesion was found to be extradural in location and was entwined among nerve roots in the sacral canal. Microscopic examination of the gross totally resected tumor revealed typical features of a choroid plexus papilloma. Despite performing a thorough neuroimaging workup (craniospinal contrast-enhanced MR imaging) for an intracranial or spinal primary mass, none was found. The choroid plexus appeared entirely normal; however, both a cavum septum pellucidum and a cavum vergae were noted. Extraneural choroid plexus papilloma, specifically intrasacral, extradural choroid plexus papilloma has not been previously reported. The present example is thought to have arisen either from ectopic choroid plexus tissue or perhaps by metaplasia from ependymal rests.