|Ahead of print
Multifocal posterior fossa pilocytic astrocytoma in a child: Case report and review of literature
Foram B Gala1, Harshal Agarwal2, Pawan Chawla2, Uday Andar2
1 Department of Radiology, Bai Jerbai Wadia Hospital for Children, Mumbai, India
2 Department of Neurosurgery, Bai Jerbai Wadia Hospital for Children, Mumbai, India
|Date of Submission||26-May-2021|
|Date of Decision||30-Nov-2021|
|Date of Acceptance||26-Dec-2021|
|Date of Web Publication||30-Jan-2023|
Foram B Gala,
Department of Radiology, Bai Jerbai Wadia Hospital for Children, Acharya Donde Marg, Parel, Mumbai 400012
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Pilocytic astrocytoma (PA) is the most common posterior fossa tumor in children; however, multifocal posterior fossa PA is very rare in children and is usually associated with risk factors such as neurofibromatosis. We described a rare case of multifocal posterior fossa PA involving pons, bilateral cerebellar hemispheres, vermis, and middle cerebellar peduncle in a child in the absence of any associated risk factor. The lesion also showed extensive areas of calcification which is also uncommon in PA.
Keywords: Multifocal pilocytic astrocytoma, pediatric tumors, posterior fossa tumors
| Introduction|| |
Pilocytic astrocytoma (PA) is the most common primary brain tumor in children with cerebellum, brainstem, optic nerve and chiasm, and thalamus/basal ganglia regions being the most common locations. This tumor has predilection to involve the midline structures. Multifocal posterior fossa PA is very rare and to the best of our knowledge, this is a first case report involving only posterior fossa in a pediatric patient in the absence of risk factors such as neurofibromatosis 1 or prior chemoradiation.
| Case Report|| |
A 5-year-old male child presented with history of difficulty in walking and standing with imbalance for the last one and half months associated with headache and multiple episodes of vomiting. He has history of delayed motor milestones in terms of delayed walking (at the age of 3 years). On examination, the child was conscious, alert without any cranial nerve palsy. He had no cutaneous markers like café au lait spots, axillary or inguinal freckling, and soft tissue nodules (neurofibromas) for neurofibromatosis. Power was preserved in all limbs. Cerebellar system examination could not be performed as the child was non-cooperative. Further evaluation with magnetic resonance imaging (MRI) of brain revealed multiple well-defined predominantly solid-enhancing lesions of varying sizes involving right side of pons, vermis, both cerebellar hemispheres as well as right middle cerebellar peduncle. The largest lesion in the right cerebellar hemisphere showed areas of necrosis. The lesions showed hypointense signal on T1W and markedly hyperintense signal on T2W images with few lesions suppressed on FLAIR images. None of the lesions showed restricted diffusion or significant perilesional edema [Figure 1]. Extensive areas of blooming were seen on SWI, which appeared bright on filtered phase images suggestive of calcification, also confirmed on computed tomography (CT) scan [Figure 2]. Few lesions showed increased perfusion, and on MR spectroscopy, very high choline peak with markedly reduced NAA and creatine peaks was obtained [Figure 3]. No leptomeningeal disease was noted. On imaging, PA was also considered as the solid lesions were markedly T2 hyperintense and showed no restricted diffusion and very less perilesional edema. Other differential diagnosis was ependymoma in view of multifocality, extensive calcification, heterogeneous appearance with solid cystic/necrotic areas. The child underwent suboccipital craniotomy with subtotal excision of the tumor. Histopathology [Figure 4] revealed astrocytic tumor of low-to-moderate cellularity composed of elongated and oval shaped cells with areas of compact and biphasic architecture. Foci of microvascular proliferation and dystrophic calcification were noted. On immunohistochemistry, tumor showed retained ATRX protein expression, few tumor cells were positive for p53 protein, and MIB-1 labeling index was approximately 3–5%. Overall findings were consistent with PA (WHO grade 1). Follow-up MRI scan was done after 3 months and showed large residual diseases involving brainstem and bilateral cerebellar hemispheres [Figure 5]. Relook surgical debulking was considered, and post-operative course was uneventful.
|Figure 1: Axial T2W (A), FLAIR (B), axial and sagittal post-contrast T1W (C and D), DWI and ADC maps (E and F) showing multiple focal solid (arrow) as well as solid-cystic lesions (elbow arrow) involving right middle cerebellar peduncle, both cerebellar hemispheres without restricted diffusion or significant perilesional edema. The lesions show heterogeneous as well as homogeneous enhancement and obliterate fourth ventricle with moderate supratentorial hydrocephalus (asterisk)|
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|Figure 2: Axial T2W images (A-C) from top to bottom show marked supratentorial hydrocephalus (asterisk) due to obstruction at the fourth ventricle by the tumor. Note lesions in the right superior cerebellar peduncle (elbow arrow), right side of pons (curved arrow), and right middle cerebellar peduncle (arrow). Rest of the lesions involve vermis and cerebellar hemispheres. Axial SWI (D and G), filtered phase (E and H), and CT scan (F and I) images showing blooming on SWI which appears bright on phase images suggestive of calcification. CT scan confirms calcification (arrow)|
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|Figure 3: Single voxel MR spectroscopy image (A) shows markedly elevated choline peak with reduction in NAA and creatine peaks. MR perfusion (B) shows most lesions being hypoperfused (elbow arrow) with few showing hyperperfusion (arrow) when compared with normal parenchyma|
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|Figure 4: Histopathological microphotographs with H&E stain. (A) Biphasic pattern—high cellularity at left (black arrow) and lower cellularity at right (white arrow) with calcification (curved arrow) (10×). (B) Round and piloid cells constitute this tumor. Note the Rosenthal fibers (white elbow arrow) and eosinophilic granular body (black elbow arrow) can be seen in higher cellular areas (40×). (C) Eosinophilic granular bodies (black elbow arrow) (20×). (D) Psammomatous calcification (curved arrow) is seen (20×)|
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|Figure 5: Follow-up: MRI scan after 3 months post-surgery. Axial T2W (A and B) and post-contrast T1 fat-saturated (C and D) images show post-operative cavity along posteromedial aspect of right cerebellar hemisphere (elbow arrow). Residual heterogeneous solid-cystic tumor is seen in the right middle cerebellar peduncle, both cerebellar hemispheres and vermis (arrows). MRI scan after second relook surgery. Axial T2W (E) and post-contrast T1 fat-saturated images (F) show large post-operative cavity in the right cerebellar hemisphere and vermis (dashed arrow). Residual tumor is also seen (arrow)|
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| Discussion|| |
PA is the most common pediatric cerebellar neoplasm accounting for 85% of all cerebellar neoplasms. It usually manifests in first two decades of life. Common presenting symptoms of this posterior fossa tumor include headache, vomiting, blurring of vision, and neck stiffness due to raised intracranial pressure. Gait disturbances as well as ataxia can occur. Brainstem lesions are additionally associated with cranial nerve (6th and 7th) palsies. PAs are regarded as grade I tumors in the WHO classification having excellent prognosis. On MRI, four imaging patterns have been described: (1) mass lesion with non-enhancing cyst with an intensely enhancing mural nodule, (2) mass lesion with enhancing cyst wall and an intensely enhancing mural nodule, (3) necrotic mass with central non-enhancing area, and (4) predominantly solid mass with minimal-to-no cystic component. Almost two-thirds of patients show patterns 1 and 2. The amount of perilesional edema is much less when compared with higher grade tumors. Imaging of our patient revealed patterns 3 and 4 with very little or no significant perilesional edema.
Multifocal glioma refers to two or more central nervous system tumors resulting from dissemination or spread via white matter tracts, cerebrospinal fluid (CSF), or local metastasis when compared with multicentric lesions, which are widely separated lesions without anatomical continuity or any clear mode of spread. Synchronous tumors occur de novo at multiple sites and present at the same time, whereas metachronous tumors have long interval between two tumors. We considered our case as multifocal PA as the lesions are in one anatomic location-posterior fossa with likely spread via white matter tracts or CSF dissemination. However, on imaging, no obvious leptomeningeal dissemination was seen, and CSF cytology was negative for malignant cells.
Multifocal PAs are seen in patients with familial tumor syndromes such as neurofibromatosis 1, Turcot or Li Freumani syndrome, prior chemoradiotherapy, or immunosuppression,,; however, our patient did not have any of these risk factors. No cutaneous markers or imaging findings classic for neurofibromatosis (optic nerve gliomas, sphenoid wing dysplasia or foci of altered signal intensity in basal ganglia, spinal nerve tumors) were seen.
A single case report of multifocal PA in an adult without associated risk factors, involving cerebellar peduncles, brainstem, and cervico-medullary junction, has been described; however, to the best of our knowledge, no such case has been described in pediatric patients involving only posterior fossa. Parenrengi and Aji described a child with multifocal PA involving cerebellum and supratentorial retrothalamic area.
Incidence of calcification in PA ranges from 12.8% to 19.7%. Calcifications usually occur in benign and slow-growing glial tumors. Mechanism of calcification is not well understood; however, degenerated tissue has alkaline pH due to reduced metabolism and reduced carbon dioxide production. Increased alkaline phosphatase also results in dystrophic calcification in degenerated tissue. There are only two case reports of extensive calcification in cerebellar PA in children, occurring as early as 6 months of age., Surgical resection with complete excision of tumor is the treatment of choice and is considered curative.
Long-term follow-up of these patients is necessary as there are chances of developing multicentric metachronous lesions as described in few case reports.
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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]