Primary tumors and other masses of the cerebellum and fourth ventricle: differential diagnosis by computed tomography

Imaging review of the temporal bone: part I. Anatomy and inflammatory and neoplastic processes

From a clinical-radiologic standpoint, there are a limited number of structures and disease entities in the temporal bone with which one must be familiar in order to proficiently interpret a computed tomographic or magnetic resonance imaging study of the temporal bone. It is helpful to examine the region in an organized and systematic fashion, going through the same checklist of key structures each time. This is the first of a two-part review that provides a practical approach to understanding temporal bone anatomy, localizing a pathologic process with a focus on inflammatory and neoplastic processes, identifying pertinent positives and negatives, and formulating a differential diagnosis.

Distinctive MRI features of pediatric medulloblastoma subtypes

OBJECTIVE

We hypothesized that the apparent diffusion coefficient (ADC) and other MRI features can be used to predict medulloblastoma histologic subtypes, as defined by the World Health Organization (WHO) in WHO Classification of Tumours of the Central Nervous System.

MATERIALS AND METHODS

A retrospective review of pediatric patients with medulloblastoma between 1989 and 2011 identified 38 patients with both pretreatment MRI and original pathology slides. The mean and minimum tumor ADC values and conventional MRI features were compared among medulloblastoma histologic subtypes.

RESULTS

The cohort of 38 patients included the following histologic subtypes: 24 classic medulloblastomas, nine large cell (LC) or anaplastic medulloblastomas, four desmoplastic medulloblastomas, and one medulloblastoma with extensive nodularity. The median age at diagnosis was 8 years (range, 1-21 years) and the median follow-up time was 33 months (range, 0-150 months). The mean ADC (× 10(-3) mm(2)/s) was lower in classic medulloblastoma (0.733 ± 0.046 [SD]) than in LC or anaplastic medulloblastoma (0.935 ± 0.127) (Mann-Whitney test, p = 0.004). Similarly, the minimum ADC was lower in classic medulloblastoma (average ± SD, 0.464 ± 0.056) than in LC or anaplastic medulloblastoma (0.630 ± 0.053) (p = 0.004). The MRI finding of focal cysts correlated with the classic and desmoplastic subtypes (Fisher exact test, p = 0.026). Leptomeningeal enhancement positively correlated with the LC or anaplastic medulloblastoma subtype and inversely correlated with the classic medulloblastoma and desmoplastic medulloblastoma subtypes (p = 0.04). Ring enhancement correlated with tumor necrosis (p = 0.022) and with the LC or anaplastic medulloblastoma histologic subtype (p < 0.001).

CONCLUSION

The LC or anaplastic medulloblastoma subtype was associated with increased ADC and with ring enhancement, the latter of which correlated with tumor necrosis. These features could be considered in the evaluation of high-risk medulloblastoma subtypes.

MR signal of the solid portion of pilocytic astrocytoma on T2-weighted images: is it useful for differentiation from medulloblastoma?

BACKGROUND AND PURPOSE

Although imaging features of cerebellar pilocytic astrocytoma and medulloblastoma have been described in many texts, original comparisons of magnetic resonance intensity between these two tumours are limited. In the present study the results of magnetic resonance imaging (MRI) were reviewed, focusing especially on the signal intensity of the solid portion of these neoplasms.

METHODS

MR images of ten cerebellar pilocytic astrocytomas and ten medulloblastomas were reviewed. The signal intensities of the solid components were graded on a scale of 1 to 5, with higher scores indicating a signal intensity closer to that of water. The degree of enhancement, tumour cysts and peripheral oedema were evaluated on MR images. When the solid portion was heterogeneous (i.e. mixed signal intensity or degree of enhancement), the dominant area was selected for evaluation.

RESULTS

On T2-weighted images, the signal intensity of the solid portion was equal to that of cerebrospinal fluid (CSF) in 50% of pilocytic astrocytomas. No medulloblastomas showed such hyperintensity. Most medulloblastomas (80%) were isointense to grey matter. On T1-weighted images, the signal intensity varied widely in pilocytic astrocytomas; however, all medulloblastomas were iso- or hypointense to grey matter. The MR enhancement pattern, cystic component and peripheral oedema all varied in both tumour types and no specific features were identified.

CONCLUSION

A signal intensity of the solid portion isointense to CSF on T2-weighted images was characteristic of cerebellar pilocytic astrocytomas; this was not observed in medulloblastomas. Attention to T2-weighted imaging of the solid portions of a tumour is easy and helpful in differentiating between cerebellar pilocytic astrocytoma and medulloblastoma.

Intraventricular gliomas

Gliomas are the most common primary brain tumor in adults, and those within or relating to the ventricular surface represent a less common but important subcategory. The most common intraventricular gliomas include ependymomas, SEs, and SEGAs. Other less common varieties have been reported, including chordoid gliomas, glioblastoma multiforme, and mixed glial-neuronal tumors. Each type of intraventricular glioma is associated with its own unique constellation of epidemiologic, clinical, radiologic, and pathologic defining characteristics. Each tumor type has its own management considerations and nuances with unique prognostic indicators and outcomes. The outcome for certain intraventricular gliomas (especially ependymomas) remains relatively poor. Future advancements in surgical technique are likely to have only a modest impact on improvement of outcome. Translational research aiming to advance the knowledge of tumor biology into new targeted cellular and molecular therapies holds tremendous promise to improve the overall outcome. Additionally, more thorough delineation of prognostic factors as well as modifications and refinements to radiation and chemotherapy may help to improve the still significantly poor outcomes for patients harboring these lesions. Future cooperative intra- and interinstitutional efforts between scientists and clinicians will hopefully culminate in an improved outlook and eventual cure for patients with gliomas.

Cerebellar astrocytomas in childhood

According to CT appearance and surgical observations, cerebellar astrocytomas can be separated into three types. On CT scan, cystic astrocytomas have a typical mural nodule; with contrast injection only the nodule becomes hyperdense; the wall of the cyst is not modified. In these cases, only the mural nodule is removed since the wall does not contain tumor cells. In contrast, false cystic astrocytomas present an irregular wall, diffusely enhanced and thick. Then the wall is invaded by tumor cells, it must be totally removed. Solid astrocytomas may invade the peduncle, the IV ventricle, and the subarachnoid spaces. Removal is sometimes questionably total. As recurrences are not frequently observed in these cases, radiotherapy is not always recommended. Rather, radiotherapy is only used in cases of undoubted partial removal or after partial removal of a recurrence. Of 63 cases, early postoperative mortality was 4.7% and late recurrence 6.3%.

Hemangioblastomas with blood supply from the dural arteries--two case reports

Hemangioblastomas are benign vascular tumors that often occur in the cerebellum, and are located near the pia mater. The blood supply is usually received through the pia mater, and rarely through the external carotid artery. The present cases of hemangioblastoma received blood supply from the external carotid artery (occipital artery) and a branch of the internal carotid artery (carotico-tympanic artery or artery of Bernasconi Cassinari) through the dural branches. The dural arteries were not the main feeders in either case, but preoperative embolization of the occipital artery contributed to minimum bleeding during the operation in one case. Incomplete resection of hemangioblastoma is related to multicentricity of the tumors, small mural nodules, or brain stem involvement. Angiography is valuable for demonstrating arterial supply to small or multiple mural nodules. Conventional angiography is necessary for investigation of the external carotid artery branches.

Calcified medulloblastoma in a child

Calcification is an unusual and atypical feature in medulloblastomas. Here we report a case of calcified medulloblastoma in a 5-year-old boy. The clinical correlation of this radiological finding is discussed.

Surgical management of haemangioblastoma of the posterior fossa

Fifty-one cases of posterior fossa haemangioblastoma have been seen in our department over a period of 23 years. Seven cases were associated with spinal cord lesions and one with a supratentorial lesion. There were 22 cases of Lindau's disease (43%). The onset was earlier and recurrences commoner than in isolated cases. In 10 cases the development of new tumours in different parts of the central nervous system (CNS) required re-operation, demonstrating the multicentric nature of this disease. The majority of the tumours occupying the fourth ventricle or medulla oblongata (8 cases) were macroscopically solid and had higher post-operative morbidity than the cystic tumours in the cerebellum. The recent development of magnetic resonance imaging (MRI) provides accurate anatomical information of the lesions (especially those of the brain stem and spinal cord) even while asymptomatic. The brilliant enhancement of these tumours on MRI with Gadolinium-diethyline-triamine-pentaacetic acid (Gd-DTPA) has proved to be particularly useful.

Posterior cranial fossa tumours in childhood

We reviewed clinical and CT findings in 133 posterior cranial fossa tumours in children. All had histological diagnosis, apart from 20 cases of brain stem glioma. The majority were intra-axial tumours, including 53 medulloblastomas (40%), 31 cerebellar astrocytomas (23%), 28 brain stem gliomas (21%), 14 ependymomas (11%), and single cases of ganglioglioma, haemangioblastoma and teratoma. Extra-axial tumours formed only 3%, including 2 chordomas and 2 schwannomas. The clinical data and CT findings are reviewed. Cerebellar astrocytoma involved the sexes equally, while medulloblastoma, brain stem glioma, and ependymoma were more common in males. Most cerebellar astrocytomas were in the midline, and presumably arose from the vermis. The frequency of calcification was similar to that in previous reports, being highest in ependymoma (69%), followed my medulloblastoma (29%), cerebellar astrocytoma (17%), and brain stem glioma (8%).

Medulloblastoma: I. Clinical, diagnostic, and therapeutic overview

Medulloblastoma, the most common embryonal tumor of the central nervous system, affects both children and adults. It poses a significant therapeutic challenge in that age-dependent differences exist, not only in their pathobiology, but in the efficacy of chemotherapy and radiotherapy. This is particularly the case in very young children, whose still developing nervous system exhibits a low tolerance to radiotherapy. We review the epidemiology, clinical presentation, radiologic features, and current therapeutic concepts relative to this unique neoplasm. Efforts are made to highlight clinical controversies.

Contribution of MRI in the diagnosis of haemangioblastomas

Magnetic resonance imaging (MRI) patterns of 11 haemangioblastomas examined with a 1.5-T scanner are described. MRI was as effective as contrast-enhanced CT in the detection of vascular tumour components, but was less sensitive than angiography. MRI was superior to CT in delineating the exact extent of the lesions, for example contact with the arachnoid surface. Even if a cystic tumour component is absent, MRI can provide helpful criteria for differential diagnosis; in particular, T2 values allow differentiation from meningiomas. In three patients additionally administered gadolinium (Gd) diethylenetriaminepenta-acetic acid (DTPA) the angiomatous parts of the tumour showed a remarkable decrease in T1 value, but the time dependence of the enhancement was not the same as that seen in dynamic CT.

Computed tomography in management of medulloblastomas

The neuroradiological studies of 116 patients with histologically verified medulloblastomas, which had been examined with plain and contrast-enhanced computed tomography (CT), were reviewed. The typical CT appearances of a well-defined, hyperdense enhancing mass in the vermis, with surrounding oedema, occurred in 60% of this series. Atypical features include calcification (17%), cystic or necrotic regions (47%) or poorly defined margins and lack of enhancement (7%). Such features in a vermis mass presenting in the first decade, especially in a boy, should not be considered against the diagnosis of medulloblastoma, but may be misleading when the tumour predominantly involves a cerebellar hemisphere.

Posterior fossa lesions in childhood and infancy. A CT study

Forty-three children with CT studies demonstrating abnormalities in the posterior fossa are presented. Tumors constitute the largest group of lesions (53.5%). Their mean size at time of diagnosis was 39.5 mm. Astrocytomas, medulloblastomas, and ependymomas were the most frequent tumors and their CT features are described and discussed. The congenital group of lesions comprised 18.6% of the cases--the most frequent anomaly being arachnoid cyst. In the miscellaneous group (23.3%), cases with atrophy were the most frequent. The cerebellar hemispheres were the most involved sites (39.5%). Lesions located at the tentorial hiatus or near the clivus were rather rare.

Computerized tomography findings in posterior fossa lesions

In 190 of 7000 brain CT studies performed between April 1978 and September 1984, abnormalities of the posterior fossa were found. Of these, 51.5% were primary tumors, 15.3% metastases, 12.1% vascular lesions and 5.8% congenital or developmental lesions. Frequencies, age and sex distribution and radiologic characteristics of the various posterior fossa pathologies are reviewed and discussed.

Cystic adult medulloblastomas

The computed tomography scans of four patients who had a medulloblastoma are reviewed. In all the cases, atypical findings were present--specifically, cystic or lucent areas within the tumor. The importance of this uncommon finding associated with adult medulloblastoma is discussed.

Posterior fossa haemangioblastomas: angiography versus computed tomography

A series of 57 patients harbouring a total of 63 haemangioblastomas of the posterior fossa is reviewed. Some clinical data are pointed out and the findings of vertebral angiography and computed tomography scanning performed in 61 and 38 lesions, respectively, are examined. The results obtained in the last 38 cases, undergoing both examinations, are compared, and some notes on differential diagnosis with other expansive lesions of the posterior fossa are given.

Haemangioblastoma of the brain. Computed tomography and angiographic studies in 17 patients

Between 1975 and 1983, 17 patients who underwent surgery for haemangioblastomas of the brain (16 lesions occurring in the posterior fossa) were studied with CT scans (17 cases) and vertebral angiograms (15 cases). The CT scans were superior for demonstrating a cystic tumour, its topography in the posterior fossa, its relationship to the fourth ventricle, and the presence and degree of an obstructive hydrocephalus. The vertebral angiographies were more sensitive and specific than CT for revealing the vascular nature, and were imperative in order to establish the supply and drainage of the tumours. It is clear that CT and angiography each make an important contribution toward defining these tumours. Their association is necessary.

Parameters of infiltration in posterior fossa tumours of childhood using a high resolution CT scanner

The computed tomographic changes in 23 posterior fossa tumours of childhood scanned on a GE 8800 scanner have been compared with the detailed operative reports in order to evaluate morphological features indicative of infiltration. The study indicated that the cyst wall of a cystic astrocytoma was always easily enucleated and was free from infiltration and that a sharp enhancing edge of a medulloblastoma or centrally necrotic astrocytoma was usually also not the site of infiltration. Other features however were found to be unreliable.

Haemangioblastomas of the posterior cranial fossa

The clinical features, diagnostic and surgical aspects of haemangioblastoma of the posterior cranial fossa are discussed in the light of a series of 61 personal cases and the published data. CT and vertebral angiography are compared as diagnostic tools. With the aid of microsurgery even haemangioblastomas of the brainstem and fourth ventricle can be removed successfully.

Computed tomography of posterior fossa ependymomas in childhood

In reviewing 10 children with surgically proven posterior fossa ependymomas, various computed tomographic representations were seen. Calcification, seen in 50% of the cases, was the single most important finding suggesting the diagnosis of ependymoma. The appearance of two of our ependymomas mimicked the "typical" appearance of medulloblastomas. A case of calcified brainstem ependymoma is presented, to our knowledge, the first such case studied with computed tomography.

Glioblastoma of the cerebellum. Computed tomographic and pathologic considerations

Cerebellar glioblastoma is a brain malignancy that is often difficult to distinguish from metastatic disease in the elderly before biopsy. The clinical course and computed tomographic appearance of four patients with multiform glioblastoma of the cerebellum are presented and correlated with other reports in the literature. The appearance of a cerebellar hemispheric lesion with little mass effect is described, and the pathology of the tumor is reviewed.

Computerized tomographic findings in medulloblastomas

Twenty patients with intracranial medulloblastoma were analyzed by CT. All patients presented with symptoms of headache, and in eight clinical findings consistent with intracranial hypertension were the only neurological abnormalities. In 16 cases, the medulloblastoma appeared as midline posterior fossa mass and in four cases it was located laterally in the cerebellar hemisphere. The fourth ventricle appeared abnormal and there was evidence of obstructive hydrocephalus in all cases. The lesion was hyperdense in 14 cases but in only one was there evidence of calcification; the neoplasm appeared isodense in six. Post-contrast enhancement was visualized in all cases; this was homogeneous in 18 and had a ring-pattern of variable thickness in two others.

Cerebellar astrocytomas in children and young adults

A clinical and pathological review of 43 cases of cerebellar astrocytomas in children and young adults was undertaken. Thirty-one of the 36 surviving patients were examined by computed tomography. Twelve patients with asymptomatic tumour were detected. Histology was necessary to identify the higher risk "diffuse" group, but no histological features helped to identify tumours liable to recur. Improvements in the prognosis may occur with long term CT scanning.

The role of computed tomography in the diagnosis and management of brain tumors

This review article emphasizes the role of computed tomography in the diagnosis and management of brain tumors. The head CT scan has become one of the most precise noninvasive tests in the neurosciences. It has given clinicians more information than they were able to obtain in the past. The subject is covered by subdividing it into several categories: detection of true tumor extent, radiation treatment planning, the immediate postoperative period, treatment responses, failure patterns, detection of radiation-induced damage, and the potential to predict histopathology. The paper is illustrated with examples that emphasize the advantages and some of the limitations of computed tomography as it exists today.

The diagnosis of solitary primary reticulum cell sarcoma of the posterior fossa with computed tomography

The CT findings in two surgically and histologically verified cases of primary reticulum cell sarcoma of the cerebellar hemisphere with secondary involvement of the cerebellopontine angle are presented. It is suggested that a correct diagnosis is possible by CT if the following criteria are present: 1. slightly increased attenuation of the mass on the precontrast scan; 2. mottled appearance of the definitely enhancing mass; 3. ill-defined borders on both the pre- and postcontrast scans; 4. degree of mass effect less than that expected from the size of the lesion; 5. involvement of the cerebellopontine angle without signs indicating an extra-axial origin of the tumor. These criteria reflect the gross and microscopic neuropathological features of the tumor.

Low-attenuation lesions in the middle cranial fossa: differential diagnosis

The reliability of cranial computed tomography (CT) in detecting a broad range of intracerebral disorders has been well established (1) and its complementary role with other neuroradiologic procedures has been documented (2). Some attempts at inferring specific histologic diagnosis from static CT scans have been made (3,4). However, other investigators have demonstrated that it is difficult to separate cystic from noncystic, benign from malignant, and neoplastic from non-neoplastic lesions by absorption coefficients alone (5,6). While initial studies utilizing dynamic CT scanning indicate that patterns of contrast accumulation may be helpful in distinguishing enhancing cerebral lesions (7,16), the differential diagnosis of the low-attenuation lesion remains difficult (17). We present a series of hypodense lesions in the middle cranial fossa that demonstrate a broad range of pathologic entities. Their CT features, differential diagnosis, and pathologic correlation are discussed.

The CT scanner in posterior fossa tumours of childhood

Eighty-five consecutive posterior fossa tumours occurring in children and detected by computed tomography (CT) were submitted to detailed analysis. There was only one false positive diagnosis, which would have been avoided with present knowledge, and no known false negative diagnoses during the same period. In most cases the histological type of the tumour could be reliably predicted. CT was less accurate for determining the anatomical extent of the lesions but tumours arising in the brainstem could always be distinguished from those predominantly affecting the fourth ventricle and cerebellum.

Double-contrast ventriculography with oxygen and water-soluble positive contrast medium, metrizamide (Amipaque)

A technique for ventriculography using both gas and a positive contrast medium metrizamide (Amipaque) is presented. This ventriculographic method proved superior to computerized tomography (CT) scanning in revealing the cause of obstructive hydrocephalus. Small central tumors and intraventricular cysts, often missed with CT, were also well demonstrated. This technique has been used since 1975, and is simple and safe.

Assessment of posterior fossa tumors in infants and children by means of computed tomography

The attenuation profiles before and after contrast enhancement were examined in 18 infants and children with posterior fossa tumors: eight cerebellar astrocytomas, six medulloblastomas, and four brainstem tumors. The astrocytomas, with one exception, had characteristic patterns, and all could be distinguished from the medulloblastomas, which have a distinct pattern of their own. The brainstem tumors had varying appearances, and were entirely low-attenuating, high-attenuating or had a ring shadow after enhancement. The nature of a posterior fossa tumor in a pediatric patient can usually be predicted fairly satisfactorily from a computed tomogram.

Unusual metastases from a medulloblastoma: case report

Calvarial and extracranial metastases by hematogenous spread of primary intracranial neoplasms have been considered a rare occurrence. This report deals with the clinicopathological and radiological findings of a child with metastatic medulloblastoma. Correlation of serial postoperative computed tomography (CT) scans and the autopsy examination indicated hematogenous calvarial and intracranial spread of the primary lesion.

The complementary nature of computed tomography and angiography in the diagnosis of cerebellar hemangioblastoma

Cerebellar hemangioblastomas were seen in seven persons, five being members of the same family. All were studied with constrast enhanced CT scans and vertebral angiograms. The CT scans were superior for demonstrating the cystic component of the tumors and associated hydrocephalus, features not usually evident on the angiograms. The angiograms were superior for revealing the vascular nature, supply and drainage of the tumors. In several patients the angiograms revealed more tumors than could be seen by CT. Both CT and angiography contribute important information in the diagnosis of these neoplasms.

Posterior fossa intra-axial tumors: a comparison of computed tomography with other imaging methods

Fifty patients with posterior fossa intra-axial tumors were evaluated by computed tomography and the results compared with routine skull films, radionuclide brain scanning vertebral angiography, and cerebral air studies. The routine skull series was found to be of little benefit. Computed tomography was more sensitive than the radionuclide brain scan in detecting all of the lesions except astrocytoma, for which sensitivity was comparable. Angiography was the most sensitive means of detecting hemangioblastoma, and was the only reliable radiographic method of differentiating hemangioblastoma from astrocytoma. Cerebral air studies were the most sensitive and specific means of evaluating brainstem gliomas.

Cerebellar hemangioblastoma: computed tomographic, angiographic and clinical correlation in seven cases

Seven patients with histologically confirmed cerebellar hemangioblastomas are reviewed in order to establish computed tomographic (CT), angiographic and clinical characteristics and correlations. Noncontrast CT scans demonstrated most cystic lesions but did not always depict nodules on the cyst wall and small solid tumors. Contrast-enhanced CT scans demonstrated the solid and cystic types of tumors but in some cases angiography better delineated them and the presence of nodules. The CT appearance reflected the pathologic characteristics, which included vascular channels, cyst formation and nodules. Solid tumors enhanced homogeneously and could not be definitively distinguished from other cerebellar neoplasms by CT alone. One atypical undifferentiated tumor appeared as a solid mass with a necrotic center. The CT appearance of associated retinal angiomatosis is also described. Hydrocephalus, gait or appendicular ataxia was the initial clinical presentation in these patients.

Low attenuation lesions in the midline posterior fossa: differential diagnosis

A wide variety of cystic appearing or low attenuation lesions in the midline posterior fossa can so closely resemble one another as to render specific histologic diagnosis from CT scans alone fraught with error. Absorption coefficients often overlap and are too nonspecific to infer consistently accurate histologic diagnosis. It is virtually impossible to separate cystic from noncystic, benign from malignant, and neoplastic from non-neoplastic lesions by absorption coefficients alone.

Impact of CT in the neurosurgical management of intracranial tumors

A total of 103 brain tumor patients examined with CT, radionuclide brain scan, and angiography or pneumoencephalography, and all surgically verified, were studied to evaluate the impact of CT on the neurosurgical handling of brain tumors. CT alone was usually sufficient for optimal handling of astrocytoma patients, angiography in most meningioma cases, and pneumoencephalography in cases with sellar, suprasellar, and some other midline tumors. Information obtained only through CT sometimes altered the therapy. Sometimes it led to biopsy instead of a meaningless attempt at a 'radical' excision: in other cases it permitted a 'radical' excision otherwise not possible.