|Year : 2022 | Volume
| Issue : 1 | Page : 74-78
Cerebellar pilocytic astrocytoma: Unusual presentation in a 3-year-old girl with classical imaging features
Austine Abebe Osawe1, Funmilola Olusola Showunmi2, Ahmadu Shehu Mohammed3, Alfred Aondoyima Tume4
1 Department of Radiology, Nigeria Navy Reference Hospital Ojo, Lagos, Nigeria
2 Department of Paediatrics, Nigeria Navy Reference Hospital Ojo, Lagos, Nigeria
3 Department of Public Health, Nigeria Navy Reference Hospital Ojo, Lagos, Nigeria
4 Department of Radiology, Federal Medical Center Gusau, Zamfara State, Nigeria
|Date of Submission||29-Nov-2021|
|Date of Acceptance||29-Sep-2022|
|Date of Web Publication||15-Nov-2022|
Dr. Austine Abebe Osawe
Department of Radiology, Nigeria Navy Reference Hospital, Ojo, Lagos
Source of Support: None, Conflict of Interest: None
Pilocytic astrocytomas (PAs) are the most common pediatric primary brain tumor. They are World Health Organization Grade 1 tumors with an excellent prognosis. In children, the cerebellum, optic nerve chiasm, and hypothalamic region are the most common locations in that order. Clinically, cranial nerve palsies, symptoms of raised intracranial pressure, and ataxia are commonly seen. We present an unusual case of PA in a 3-year-old toddler with inability to walk. High index of suspicion is required for the diagnosis of posterior fossa tumors in this age group as they can deteriorate rapidly.
Keywords: Astrocytoma, hydrocephalus, imaging
|How to cite this article:|
Osawe AA, Showunmi FO, Mohammed AS, Tume AA. Cerebellar pilocytic astrocytoma: Unusual presentation in a 3-year-old girl with classical imaging features. West Afr J Radiol 2022;29:74-8
|How to cite this URL:|
Osawe AA, Showunmi FO, Mohammed AS, Tume AA. Cerebellar pilocytic astrocytoma: Unusual presentation in a 3-year-old girl with classical imaging features. West Afr J Radiol [serial online] 2022 [cited 2022 Dec 1];29:74-8. Available from: https://www.wajradiology.org/text.asp?2022/29/1/74/361190
| Introduction|| |
Pilocytic astrocytoma (PA), previously known as spongioblastoma, is a histologic subtype of astrocytoma, classified as World Health Organization (WHO) Grade I, with a rather benign, slow-growing biological behavior.
It constitutes 85% of all cerebellar astrocytoma and 10% of all cerebral astrocytoma in this age group. Overall, it accounts for 0.6%–5.1% of all intracranial neoplasms and 1.7%–7% of all glia tumors.
Although genetic determinants are recognized in astrocytoma development and progression, astrocytomas do not differ intrinsically in incidence or behavior among racial groups.
No clear sex predominance has been identified in the development of PAs. However, a slight male predominance, with a male-to-female ratio of 1.18:1 for the development of low-grade astrocytomas, has been reported.
We present an interesting case of a 3-year-old girl with inability to walk whose imaging features were classical for cerebellar PA.
| Case Report|| |
A 3-year-old toddler brought to the Nigerian Navy Reference Hospital Ojo children outpatient clinic on account of inability to walk, neck pain, and tremors in left hand when trying to reach or hold objects all of 2-week duration. The parents of the child admitted that symptoms were gradual in onset and progressively worsened before presentation. No history of loss of consciousness but there was a positive history of headaches. No associated fever or vomiting.
Her pregnancy was booked at 4 months and her mother had regular antenatal care at a private facility. Delivery was at term through spontaneous vaginal delivery and was uneventful. The child was fully immunized according to schedule, and developmental milestones were attained at appropriate times. She gained neck control at 3 months and started sitting without support at 4 months, crawled at 5 months, and walked at 1 year.
Physical examination revealed a conscious and alert child with no abnormal area of skin pigmentation or nodulation to suggest neurocutaneous disorder.
Patient's vital signs were stable with blood pressure of 115/80 mmHg, pulse rate of 124 bpm, and respiratory rate of 24 cycles/min.
Neurologic examination revealed intact cranial nerves. Memory and speech were adequate for age and tone was normal on all limbs. Power on the limbs was reduced being 3 on the right upper and lower limbs and 4 on the left. Sensations and reflexes were normal.
Routine blood test results were essentially normal. Magnetic resonance imaging (MRI) of the brain [Figure 1],[Figure 2],[Figure 3],[Figure 4] demonstrated cystic posterior fossa mass with enhancing walls and an intensely enhancing mural nodule. The mass was predominantly involving the left cerebellar hemisphere and compressed the 4th ventricle with consequent obstructive hydrocephalus. These features were consistent with cerebellar PA.
|Figure 1: Mid sagittal T1W noncontrast MR image of the brain shows a large posterior fossa mass with predominantly cystic component and mural nodule causing effacement of the 4th ventricle with consequent hydrocephalus. MR - Magnetic resonance|
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|Figure 2: Axial T1W Fat saturated (FS) postgadolinium image of the brain demonstrating a cystic left cerebellar lesion with enhancing walls and mural nodule. Dilated 4th ventricle and inferior horns of the lateral ventricles are noted due to cerebrospinal fluid flow obstruction|
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|Figure 3: Coronal T2W MR image of the brain shows mixed signal intensity mass in left cerebellar hemisphere with prominent horns of the lateral ventricles and periventricular CSF seepage due to obstruction at foramen of Monro|
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|Figure 4: Post-op sagittal T2W MR image of the brain and cervical spine shows signal alteration in the mid and inferior cerebella parenchyma with persistent lateral ventricular dilatation and subocipital fluid collection|
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| Discussion|| |
Astrocytomas are classified according to a grading system developed by the WHO. They come in four grades based on how fast the cells are dividing and the likelihood that they will infiltrate nearby tissues. Grades I or II are nonmalignant and may be referred to as low-grade, whereas Grades III and IV are malignant and may be referred to as high grades.
PAs are Grade I tumors with less potential of becoming malignant. Anaplastic astrocytomas are Grade III astrocytomas, whereas glioblastoma multiforme are Grade IV astrocytomas.
PAs occur at a rate of 2 in 100,000 people mainly under 20 years of age. They can arise anywhere in the central nervous system, although most frequently in the cerebellum (42%), followed by the supratentorial compartment (36%), the optic pathway and hypothalamus (9%), brainstem (9%), and the spinal cord (2%). PA is found in 15%–21% of Neurofibromatosis 1 (NF1) patients.
In children, the most common site affected is the cerebellum (67%), with only rare cases developing supratentorially. The typical imaging appearance is a well-circumscribed cystic lesion with enhancing mural nodule. However, other presentations including heterogeneously solid, multicystic, and occasionally hemorrhagic masses may be encountered.
Presentation will generally be insidious as in the index case due to the slow growth of the tumor and the identification of early symptoms will be dependent on localization and the ability of the patient to communicate neurological changes resulting from the tumor.
Patients with PA present in different ways depending on the tumor site. Headache, vomiting, gait disturbance, blurred vision, diplopia, and neck pain are common symptoms. In cases involving the cerebral hemispheres, hemiparesis, ataxia, and seizure activities indicating cortical gray matter involvement are commonly seen in addition to other features of raised intracranial pressure.
The index patient presented with neck pain, headache, poor neck control, appendicular dysmetria, and inability to walk, the latter being unusual as gait disturbance is a more common presentation with cerebellar involvement.
A search through literature did not show any report of inability to walk as a pattern of presentation of PA and this informed the decision to report this case as peculiar. There were initial diagnostic difficulties on the part of the clinician which were resolved on imaging.
The association of PA with NF-1 is well-documented as cytogenetic studies have shown losses of genetic material in the long arm of chromosome 17 (17q) near the same locus for the NF-1 tumor suppressor genes. The cerebellum is an uncommon location for tumors in patients with NF-1. There were no features in our patient to suggest the presence of neurocutaneous disease.
When present in the optic pathways, the tumors may produce the loss of visual acuity or field defects and when localized to the hypothalamus, may result in endocrine syndromes, such as diabetes insipidus, precocious puberty, or electrolyte imbalance.
Imaging, particularly computed tomography (CT) and MRI play key roles in tumor identification, characterization, and grading. Four predominant imaging patterns of PAs on MRI following intravenous gadolinium administration have been described – I: Cyst-like mass with enhancing cyst wall and intensely enhancing mural nodule (46%), II: Cyst-like mass with a nonenhancing cyst wall and an intensely enhancing mural nodule (21%), III: Necrotic mass with a central nonenhancing zone (16%), and IV: Predominantly solid mass with minimal-to-no cyst-like component (17%).
The cystic component demonstrates hyperintense, near-fluid signal on T2W imaging and facilitated diffusion. It may have a variable signal on T2 fluid-attenuated inversion recovery imaging due to proteinaceous contents. The solid portion is of variable size and proportion, ranging from a mural nodule at the periphery of the cyst to a less common completely solid lesion. The solid component does not restrict diffusion, with reported apparent diffusion coefficient values of 1.13 to 1.92 x 10-3 mm2/s, which is a distinguishing feature from high-grade tumors such as medulloblastoma.
On magnetic resonance (MR) perfusion, there is often increased relative cerebral blood volume in the solid component, and on MR spectroscopy there may be significantly elevated choline, despite the low-grade nature of the tumor. High lipid/lactate peaks are common in PAs. On CT scans, most supratentorial low-grade astrocytomas are hypodense with variable contrast enhancement. Calcifications may be present. High-grade tumors show a more heterogeneous density pattern and a more diffuse contrast enhancement. Patients with cerebellar astrocytomas may demonstrate hydrocephalus and contrast enhancement on CT scans.
Angiography may be used to rule out vascular malformations and to evaluate tumor blood supply. A normal angiographic pattern or a pattern consistent with an avascular mass that displaces normal vessels is usually observed with both low-grade and high-grade lesions.
Histologically, PA manifests in a biphasic pattern, composed of a combination of loose glial components of multifocal myxoid changes and compacted piloid tissue as seen in [Figure 5]. The piloid tissue is composed of dense sheets of elongated bipolar cells that demonstrate fine fibrillary processes and abundant Rosenthal fibers.
|Figure 5: Histopathology picture of the tumor specimen showing sheets of pilocytic cells on fibrillary background with eosinophilic granules|
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PAs have numerous oddities; they can simulate aggressive tumors in their ability to infiltrate surrounding brain tissues and demonstrates intense enhancement pattern similar to high-grade neoplasm. They could metastasize (rare) without associated increased mortality and they could resolve spontaneously in patients with NF1.
Postoperative MRI is important as part of case management as it enables the assessment of extent of surgical resection and the detection of residual disease. Postoperative MRI evaluation should be performed within 72 h of surgery to delineate residual tumor from the postsurgical inflammatory changes that are visualized on MRI at this time. The postoperative MRI of our patient [Figure 4] revealed complete resection of the tumor with no evidence of postoperative inflammatory changes.
Common differential diagnosis of PA includes hemangioblastomas, medulloblastomas, ependymomas, rhabdoid tumors, and gangliogliomas.
The main differential diagnosis, hemangioblastoma commonly occurs in the older age group. They demonstrate flow voids arising from serpiginous supplying vessels and there is usually associated peritumoral edema. In children, they occur in association with Von Hippel–Lindau diseases. The cyst walls in these lesions usually do not enhance on intravenous gadolinium administration and they do not show calcifications.
Medulloblastomas typically arise from the midline, especially the vermix and the roof of the 4th ventricle rather than the cerebella hemisphere. Ependymomas tend to fill the 4th ventricle and protrude out of the foramen of Luschka and foramina of Magendie. Large cystic components are less common in these lesions. Rhabdoid tumors are larger heterogeneously enhancing masses while gangliogliomas show variable appearance on imaging from partially cystic mass with enhancing mural nodule to solid mass expanding the overlying gyrus. They demonstrate variable contrast enhancement.
PAs are primarily treated by surgery. This may be followed up by radiotherapy, particularly when there has been incomplete resection. Chemotherapy may be given in some cases where the tumor progresses, especially where further surgery is not possible. Treated with resection, low-grade cerebellar astrocytoma has rewarding long-term prognosis with overall 10-year survival reported to be over 90%.
Our patient had suboccipital craniotomy and excision of tumor [Figure 6] with follow up radiotherapy. Histology of the specimen [Figure 5] confirmed tumor as PA. She has had a few postoperative follow-up visits to the clinic and has done remarkably well. She has regained the ability to walk and has remained stable.
|Figure 6: Photograph of the resected tumor showing the presence of characteristic multiple cystic structures within the mass|
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]