CASE 2

Patient: Female, 5-months-old.

Chief complaint: Head circumference was increased for a month.

HPC (History of Presenting Complaint): A girl with intelligence and physique developmental delay was found head circumference increased for 1 month. She was associated with no fever, convulsions, nausea, vomiting, irritability, scream, limbs tremor and incontinence.

Past medical history: Her familial medical history was unremarkable.

Physiological and neurologic examinations: Her head circumference was 49 cm and anterior fontanelle was with the size of 4×5cm. Neurologic examination performed at a tense anterior fontanelle. Other was normal.

Laboratory examination: Normal.

【Imaging】CT examination: Toshiba 64 slices spiral CT examination. Scan parameters: the tube voltage: 120 kv; the current 80 ma, the thickness 5 mm.

Fig 1a Fig 1b

Fig 1a-1b：Axial CT showed a slightly hyper-attenuated mass in the cerebellum with edema, resulting

in obstructive hydrocephalus.

MR examination: 1.5T brain MRI (Philips). The following pediatric brain MRI sequences were performed: T2-weithted (TR/TE, 2773/150), FLAIR (TR/TE, 11000/140), and unenhanced T1 weighted (TR range/TE, 604/15) and contrast-enhanced T1 weighted. A 5-mm section thickness with a 0.5- mm skip was used. And axial diffusion-weighted images (b=800 s/mm2) were available.

Fig2a Fig 2b Fig 2c Fig 2dFig 2a-2d (Axial view MR images): 2a-2d showed an equivocal nodularity with high T2-weighted /FLAIR signal intensity and low T1-weight signal in the tumor to gray matter. Contrast-enhanced T1-weighted image reveals a grape-like enhancing tumor occupying the upper part of the posterior fossa.

Fig 3a Fig 4a Fig 3a (Sagittal view MR images): showed the grapelike nodular lesion occupying the upper part of the posterior fossa is contained in a large well-delimited macrocyst separating the tumor from the surrounding brain.

Fig 4a (Coronary view MR images): showed the grape-like enhancing tumor occupying the upper part of the posterior fossa leaded to obstructive hydrocephalus.

Fig 5a Fig 6aFig 5a (Axial view ADC images): 7ashowed the tumor node and the macrocyst were both low signal in ADC imaging.

Fig6a (Axial view DWI images, b=800): showed the tumor’s nodes were high signal in DWI but cyst was low signal.

T2WI T1WI FLAIR +C

+C

B=800

+C

ADC

【Radiodiagnoses】A: MedulloblastomasB: Hemangioblastoma C: Parasitic infectionsD: TuberculosisE: Juvenile pylocytic astrocytoma, JPA

【Diagnostic Clues】1、 What is the most likely diagnosis? (Answer: A)

2、 What is the differential diagnosis?

3、 Please describe the chief imaging features of MB?

4、 What is the key points of this kind of MB?

5、 What is the reason of misdiagnosis in this case?

【DIAGNOSTIC CHECKLIST】

1、Best imaging clues

CT: The mass was origin from the midline area of posterior fossa. Plain CT showed hyperdense mass with litter edema, resulting in obstructive hydrocephalus.

MRI: The mass was extensive nodularity with hypointense in T1-weight and hyerintense in T2-weight with litter edema. In ADC and DWI imaging also showed the extensive nodularity was hypritense. Contrast-enhanced T1-weighted image reveals a grape-like enhancing tumor in a large well-delimited macrocyst separating the tumor from the surrounding brain, occupying the upper part of the posterior fossa. Pre- and post-contrast sagittal images showed the tumor was origin from the fourth ventricle roof (superior medullary velum).

2、Image Interpretation Pearls

（1） Imaging Recommendations：Both CT and MR can display where the tumor from (the roof of

posterior fossa), but MR scan can offer more information than CT, such as soft

resolution，anatomical details and parameters to different diagnoses. In this case, MR scan

showed grapelike nodular lesion occupying the upper part of the posterior fossa was contained in a large well-delimited macrocyst separating the tumor from the surrounding brain which could’t find in CT scan.

（2） Localization Diagnosis: Axial, coronal and sagittal imaging showed that the tumor was derived

from the roof of the fourth ventricle, leading the fourth ventricle been flat and moved forward. It was a grape-like enhancing tumor occupying the upper part of the posterior fossa leaded to obstructive hydrocephalus. By far, the most common posterior fossa tumors of childhood are medulloblastomas, astrocytomas (of the cerebellum and brainstem), ATRT, and ependymomas.

（3） Etiologic Diagnosis： The male infant, experienced normal development until 4 months of age,

when he presented with increasing of the head circumference. Physiological and neurologic examinations performed at a tense anterior fontanelle. The solid tumor components were iso- or slightly hyperdense to cerebral cortex on CT scans and slightly hypointense on T1-weighted MR images. On T2-weighted images they were hypointense and showed marked contrast enhancement after intravenous gadolinium administration. Contrast-enhanced T1-weighted image reveals a grape-like enhancing tumor in a large well-delimited macrocyst was derived from the roof of the fourth ventricle, occupying the upper part of the posterior fossa and leading to obstructive hydrocephalus. Preoperative diagnosis is not easy.

【Differential Diagnoses】1、 Image Interpretation Pearls : Best imaging tool: Pre- and post-contrast sagittal images to show

site of origin (roof). Medulloblastomas was hyperdense(90% ) on CT plain, hypointense to gray matter (GM) on T1WI and hyperintense on T2WI, with heterogeneous enhancement. But remember, medulloblastoma can also be with extensive nodularity, which had been called cerebellar neuroblastoma, and it is a rare brain tumor.

2、 Differential Diagnoses

（1） Ependymoma: Ependymomas constitute 8% to 12% of primary CNS neoplasms in children and

10% to 20% of posterior fossa tumors in children. In childhood, intracranial ependymomas are more commonly infratentorial (70%) than supratentorial (30%). There is a slightly increased preponderance in males. Ependymomas of the posterior fossa have two age peaks, the first occurring between the ages of 1 and 5 years and the second in the middle of the fourth decade. Patients with ependymomas of the posterior fossa frequently present with a long clinical history. Most ependymomas are solid in nature, with calcification seen in up to 50% of posterior fossa ependymomas and cysts in approximately 20%. Posterior fossa ependymomas originate from the sides of the medullary portion of the fourth ventricle. The most important imaging finding to identify ependymomas is extension of the tumor through the fourth ventricular outflow foramina. The most characteristic appearance of a posterior fossa ependymoma on CT is that of an iso- to hyperdense (compared to gray matter) posterior fossa mass, with punctate calcifications small cysts, and moderate, heterogeneous enhancement after intravenous contrast administration. T1-weighted images commonly reveal a slightly hypointense. T2-weighted images reveal a mass that is usually isointense with gray matter; foci of high intensity (necrotic areas or cysts) and low intensity (calcifications or hemorrhage) may be present within the tumor mass.

Fig7a Fig7b Fig7c

Fig7d Fig7e Fig7f

（2） Cerebellar Astrocytomas: Astrocytomas are the most common brain tumor in children, accounting

for 40% to 50% of primary pediatric intracranial neoplasms. Approximately 60% of astrocytomas are located in the posterior fossa with 40% in the cerebellum and 20% in the brainstem. Most cerebellar astrocytomas in children are of a specific histological type, called juvenile pilocytic astrocytoma (JPA), which is considered a unique tumor and is classified as grade I by the World Health Organization. The peak incidence of these tumors is from birth to 9 years of age. The typical appearance of cerebellar astrocytoma is that of a large vermian or hemispheric tumor that is predominantly cystic. The solid portion of the tumor is usually isodense to hypodense to normal white matter on noncontrast CT, with pilocytic tumors nearly always hypodense; high-grade tumors may be hyperdense. Contrast enhancement is usually irregular, half of the lesions showing mixed attenuation. In general, solid portions appear as low-signal intensity masses on T1-weighted sequences and as high-intensity masses on T2-weighted and FLAIR sequences. Solid portions of tumor will enhance with paramagnetic contrast in an identical fashion to their enhancement with iodinated contrast on CT.

Fig8a Fig8b Fig8c

T2WIT1WI FLAIR

+C +C +C

T2WI T1WI FLAIR

Fig8d Fig8e Fig8f

Fig8g Fig8h Fig8i

（3） Hemangioblastoma (HB): Cerebellar hemangioblastomas are present in more than half of patients

with von Hippel-Lindau disease. Hemangioblastomas may develop in childhood before the age of 10 years, in the teen years, or in early adulthood. The most common locations are the spinal cord (50%), cerebellum (38%), brain- stem (10%), and cerebrum (2%). Between 20% and 40% of the tumors are solid. When the nodules of hemangioblastoma are large enough, they will show contrast enhancement on CT. The MR appearance of the cystic lesions is that of sharply marginated, peripheral cerebellar masses showing T1 hypointensity and T2/FLAIR hyperintensity. Precontrast and postcontrast T1-weighted sequences are the most useful for detection of hemangioblastomas.

（4） Metastatic Tumor: History of primary tumor.

Pathology and Surgery

1、 Surgery Finding: The tumor was origin from the roof of fourth ventricle（cerebellar vermis）. It

was grey-white firm tumor measuring 5×5×4cm in aggregate with a clearly boundary, gray nodular appearance.

2、 Pathological Findings: There were highly malignant tumors composed of very primitive,

undifferentiated small, round cells, being arranged in parallel rows. The tumor cell is densely packed hyperchromatic cells with scanty cytoplasm, visible part of the small nucleoli. Nuclear fission and mitoses could be seen in in some areas. Abundant reticulin fibers and mitoses were absent in typical pale island areas.

+C +C +C

+C B=800 ADC

Immunohistochemical: Vimentin(+)，NSE(+)，Desmin(-)，GFAP(-)，CD99 partial (+)，KI-

67(60%+)，yn partial (+)，CgA(-)，S-100(-)，Ini-1(+)。Pathological Diagnosis: (cerebellum) malignant small round cell tumor, accord with medulloblastoma, nodular type/promote fiber hyperplasia.

Fig 7a Fig 7b Fig 7a: General pathological showed the tumor had a clearly boundary, gray nodular appearance and arranged in a grape-like configuration.Fig 7b: H & E, original magnification×100. There were highly malignant tumors composed of very primitive, undifferentiated small, round cells, being arranged in parallel rows. The tumor cell is densely packed hyperchromatic cells with scanty cytoplasm, visible part of the small nucleoli. Nuclear fission and mitoses could be seen in in some areas. Abundant reticulin fibers and mitoses were absent in typical pale island areas.

【Opinion of Medical Radiation Technologists】This case was the atypical manifestation of a common tumor in children, and preoperative

diagnosis was difficult. Contrast-enhanced T1-weighted image reveals a grape-like enhancing tumor in a large well-delimited macrocyst was occupying the upper part of the posterior fossa. But we can also find the tumor was derived from the roof of the fourth ventricle with hyperdense on CT scans, hypointense on T1-weighted images and hyperintense on T2-weighted. The nodules were low signal in ADC and high singal in DWI imaging. All clues can be prompt as medulloblastoma.

Medulloblastomas(MB) are highly malignant tumors composed of very primitive, undifferentiated small, round cells and are highly malignant (WHO grade IV). In children, medulloblastoma is the second most common brain tumor (after astrocytoma) and the most common malignant brain tumor (15%–20% of intracranial neoplasms in children); it is the most common posterior fossa tumor in most series (30%–40% of posterior fossa neoplasms), being slightly more common than the cerebellar astrocytoma. It is the most common tumor in the 6 to 11 year age group with a slightly increased preponderance in males. The most common symptoms are headaches, vomiting, and nausea. In children less than 1 year of age, increasing head size and lethargy are frequent presenting symptoms. It have poor prognosis under the age of 3. Ten years survival rate was 60% and 75% patients were postoperative recurrence in 2 years.

It appears likely that medulloblastoma derives from BTSC, mutated precursor cells that compose the small but actively proliferating component of the tumor. The tumor usually forms a well-defined vermian

mass widening the space between the cerebellar tonsils. Anteriorly, it impinges upon the roof of the fourth ventricle and causes partial or complete obstruction to CSF flow. Pathologically, subarachnoid tumor appears as small grayish patches of tumor or as a continuous “frosting” of tumor on the pia. Heterogeneity probably results from the cysts and calcification.

The tumors are most commonly situated within the inferior vermis. On CT, a typical medulloblastoma classically appears as a well-defined, hyperdense tumor of the cerebellar vermis or vermis and hemisphere. As a result of their composition of small, round cells with a high nuclear to cytoplasmic ratio, medulloblastomas are almost always hyperdense or isodense compared to surrounding white matter prior to the administration of intravenous contrast. Mild to moderate edema surrounds the tumor in approximately 90% of patients. Hydrocephalus is present in approximately 95% of patients at the time of presentation. Enhancement is seen in greater than 90% of medulloblastomas, most commonly diffuse, but sometimes irregular or even absent. On MRI, the most common appearance is that of a round, slightly lobulated mass, isointense to normal gray matter on T1-weighted images. T2-weighted sequences typically reveal a heterogeneous mass in which the solid portions are hypointense or isointense compared to gray matter.The enhancement pattern of the tumors after intravenous infusion of paramagnetic contrast is variable; enhancement may be patchy or uniform.

The latest WHO classification of the tumors of the CNS describes several subtypes, all grade IV: the classic medulloblastoma (65%–75%), desmoplastic medulloblastoma (7%), medulloblastoma with extensive nodularity (3%), anaplastic medulloblastoma (10%– 22%), and large cell medulloblastoma (2%–4%). Medulloblastomas characterized by extreme nodularity, intranodular nuclear uniformity, and cell streaming in a fine fibrillary background are called “cerebellar neuroblastoma.” They are also located in the cerebellar hemispheres of infants younger than 3 years.

The solid tumor components were iso-or slightly hyperdense to cerebral cortex on CT scans and slightly hypointense on T1-weighted MR images. On T2-weighted images they were hypointense and showed marked contrast enhancement after intravenous gadolinium administration. Contrast-enhanced T1-weighted image reveals a grape-like enhancing tumor was derived from the roof of the fourth ventricle.

30-40% MB may transfer before surgery. CSF spread of tumor is very poorly evaluated by noncontrast MRI. Therefore, paramagnetic contrast should be used in the evaluation of these patients both prior to and after resection of the tumor. The most common locations for intracranial metastases are the vermian and basilar cisterns, subependymal region of the lateral ventricles, and the subfrontal region. Intraventricular (subependymal) metastases frequently show limited enhancement; this should not cause confusion in the proper clinical setting, as periventricular nodular heterotopia are rarely seen as incidental findings.

On contrast-enhanced MRI, drop metastases may appear as a smooth enhancing coating of the spinal cord or as brightly enhancing foci in the extramedullary, intradural and, occasionally, intramedullary space. The most common location is along the posterior surface of the spinal cord in the thoracolumbar regions (along the arachnoid septum that attaches the dorsal cord to the posterior dura, known as the septum posticum); the caudalmost aspect of the thecal sac is also frequently involved.

DWI and ADC imaging can better identify cerebellar tumor. The small round cells also result in the solid regions of the tumor being hyperintense compared with normal cerebellar tissue on DWI and hypointense on diffusivity maps. The signal intensities presumably relate to reduced amount of free water within the tumor. So medulloblastoma is the highest signal in DWI imaging and the lowest signal in ADC imaging. Cerebellar astrocytomas contain less solid regions, so it is the lowest signal in DWI and the highest in DWI imaging. And ependymoma is somewhere between them. Table 1-1 is summaried the differential diagnosis of posterior fossa tumors in children.

Table 1-1 Differential diagnosis of posterior fossa tumors in childrenType CT value T1WI DWI ADC

medulloblastomahyperdense /

isodensehypointense

hyperintens

e（++）hypointense（+

+）ependymoma isodense Isointense

hyperintens

e（+）hypointens

e（+）astrocytomas hypodense hypointense hypointense hyperintense

References

1. Leslie C. Hellbusch Mark N. Robinson Rodney D. McComb et al. Medulloblastoma with Extensive Nodularity: A Report of Two Cases. Pediatr Neurosurg 2008;44:430–432.

2. Brian D. Coley, MD. Caffey’s Pediatric Diagnostic Imaging (Twelfth Edition). Copyright 2013 by Saunders, an imprint of Elsevier Inc.

3. A. James Barkovich, MD Diagnostic Imaging Pediatric Neuroradiology(Second edition) Copyright 2015 by Elsevier.

4. Daniel Chelliah, Christian Mensah Sarfo-Poku, Baldassarre D. Stea, et .al.Medulloblastoma with Extensive Nodularity Undergoing Post-Therapeutic Maturation to a Gangliocytoma: A Case Report and Literature Review. Pediatr Neurosurg 2010;46:381–384.