|Ahead of print
Clival atypical teratoid/rhabdoid tumor: A diagnostic dilemma
Pallavi Sinha1, Rachna Seth2, Kavneet Kaur3, Manisha Jana1
1 Department of Radiodiagnosis and Intervention Radiology, All India Institute of Medical Sciences, New Delhi, India
2 Department of Paediatrics, All India Institute of Medical Sciences, New Delhi, India
3 Department of Pathology, All India Institute of Medical Sciences, New Delhi, India
|Date of Submission||09-Jul-2021|
|Date of Decision||14-Nov-2021|
|Date of Acceptance||14-Nov-2021|
|Date of Web Publication||07-Jan-2022|
Department of Radiodiagnosis and Intervention Radiology, AIIMS, Ansari Nagar, New Delhi.
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Primary central nervous system atypical teratoid/rhabdoid tumor (AT/RT) is a highly aggressive, malignant tumor, which occurs in infancy and early childhood. It is a rare tumor with a posterior fossa predilection, arises in the posterior fossa in an off-midline location, and may secondarily involve bones. Optimal treatment for ATRT remains unclear due to paucity of literature. Treatment options include surgery, radiotherapy, and chemotherapy. The prognosis is dismal with low rates of survival. Herein, we describe an unusual site of origin of AT/RT, the clivus. The imaging findings were elusive and definitive diagnosis was made on histopathology.
Keywords: Atypical teratoid rhabdoid tumor, MRI, teratoid rhabdoid tumor
| Introduction|| |
Atypical teratoid/rhabdoid tumor (AT/RT) of the central nervous system is a rare, aggressive, malignant tumor of childhood. ATRT was first described as a histological variant of Wilm’s tumor, which mainly occurs in infants and has unfavorable prognosis.
On routine histopathologic examination, misdiagnosis of some ATRTs as medulloblastoma is common and immunohistochemistry (IHC) is used for differentiation. Imaging features are also variable, and not always diagnostic.
| Case Report|| |
A 2-year and 4-month-old boy presented to our institute with features of raised intracranial tension (vomiting and vertigo). On the fundus examination, there was papilledema. He had no motor or sensory deficits, was afebrile, no pallor or peripheral lymphadenopathy. Five months before, he underwent surgical resection of an intracranial tumor at a private institution. Imaging at the first presentation revealed a midline clival mass [Figure 1]. It was diagnosed as ATRT on histopathology. After surgical resection, he underwent conventional cranial external beam radiotherapy (EBRT)-45 Gy plus 10 Gy at 30 days postoperative, and was asymptomatic for 5 months.
|Figure 1: A–C: Preoperative images of a 2-year-old male child [Fig A, B, C] T2W-Sag- shows a large T2 hypointense-isointense lesion involving the clivus. No intraparenchymal component seen. T1W-Axial-isointense lesion with epicentre in (R) clival location. T1-PG-lesion shows heterogeneous post contrast enhancement.|
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Imaging at the recent presentation revealed a recurrence of the mass. There was a heterogeneously enhancing lesion epicentered in the clivus with a large soft tissue component. Contrast-enhanced MRI of the spine was also done in keeping with the high predilection of these tumors for cerebrospinal fluid (CSF) and leptomeningeal spread. Multiple subcentimeter-sized homogeneously enhancing extramedullary soft tissues were noted in cervical and thoracic spine [Figure 2].
|Figure 2: A–F: MRI at the age of 2 years and 8 months shows-T1W axial-post contrast image heterogeneously enhancing lesion at the primary site. T2W sagittal [arrow in B] and T1 post contrast [arrow in C] images show hypointense to isointense lesion involving the clivus with a large soft tissue component in the premedullary region just inferior to the Pons. The lesion shows restricted diffusion [arrow in D, E]. Axial T1 w postcontrast image of thoracic spine shows an extramedullary enhancing lesion suggestive of cerebrospinal fluid (CSF) dissemination [arrow in F].|
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Considering the significant clinical history and imaging appearance, recurrence of the primary tumor was considered. A repeat biopsy was taken to ascertain histopathology; since this was an unusual site for ATRT. Histopathology review at our institute revealed a cellular tumor comprising sheets of tumor cells with moderate amount of dense eosinophilic cytoplasm, eccentric nuclei with vesicular chromatin and prominent nucleoli Few characteristic rhabdoid cells with intracytoplasmic eosinophilic inclusions were also identified. Frequent mitotic figures, high MIB-1 labeling index, and areas of necrosis were noted. On IHC, the tumor cells displayed epithelial differentiation in the form of cytokeratin positivity and showed loss of nuclear SMARCB1 (INI-1) protein expression [Figure 3]. The attendants refused further treatment after prognostication and the child succumbed after 5 months.
|Figure 3: Cellular tumor comprising cells with bright eosinophilic cytoplasm and eccentric nuclei (×200) [A]; high power magnification showing rhabdoid cells (arrowhead) and mitotic figures (arrow) (×400) [B] along with foci of necrosis (arrowhead) (×200) [C]; Immunohistochemistry revealed immunopositivity for cytokeratin [D]; loss of INI1 nuclear expression [E] and high MIB1 labeling index [F].|
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| Discussion|| |
Central nervous system ATRT is a rare, highly aggressive tumor of early childhood. They include 1.5%–3% of tumors in children less than 18 years old. Majority of the patients present at less than 3 years of age. It has a slight female preponderance (M:F-1:2).
Majority of these tumors (approximately two-thirds) are infratentorial; the most common location being cerebellum., Other areas include the cerebral hemispheres, the pineal region, and the spine. Amongst the unusual imaging features in this child, the most notable was its location, bony origin from clivus. This is an extremely uncommon site for ATRT, with only in two cases described in the literature, [Table 1]. Mostly, they are intraparenchymal, with secondary bony involvement. Up to one-third of patients have CSF dissemination at diagnosis, similar to our case.
Typical imaging features are described in various case series and case reports,,:
These tumors have a predilection for the posterior fossa, with a tendency to occur off midline. On imaging, they are usually bulky heterogeneous masses with eccentric cysts (with enhancing walls) between the solid component and adjacent brain. Hemorrhage is common in these tumors and they show restricted diffusion. Paucity of perifocal edema is noted. They can show hyperdensity on non-contrast CT scans, due to increased cellularity, and microscopic calcification. However, visible calcification on imaging is unusual.
Primitive neuroectodermal tumor (PNET) is a tumor that can closely mimic the appearance of ATRT. Other extra-axial tumors that can present at this age include chordoma, neuroblastoma metastasis, Ewing’s sarcoma, Langerhan’s cell histiocytosis (LCH), and lymphoma.
PNET/MB is very similar to ATRT on imaging and is usually distinguished by IHC. But cerebellopontine angle (CPA) involvement and hemorrhage are more common in ATRT. Medulloblastoma, in contrast, is usually midline and CPA involvement is seen less often.
Clival chordoma is extremely T2 hyperintense due to physaliphorous cells in contrast to ATRT, which is isointense to slightly hyperintense. It presents as a midline mass indenting the pons; this characteristic appearance has been termed as thumb sign. Calcification is noted in about 30–40% cases. Mild heterogeneous enhancement is seen, unlike our case, which showed avid enhancement. It can be differentiated from ATRT on imaging alone, and also the age at presentation is higher for chordomas.
Ewing Sarcoma of Clivus is a very rare tumor and has similar imaging characteristics but shows a predilection for petrous bone and cavernous sinus extension. Age of presentation is second decade or higher. The lesion is hyperintense on T2.
LCH of clivus on MRI shows abnormal marrow signal with homogeneously or heterogeneously enhancing destructive soft tissue mass. It is hyperintense on T2 and hypointense on T1-weighted images. Diffusion restriction may be seen. The involvement of petrous ridge is commonly seen.
Imaging characteristics of metastatic neuroblastoma are nonspecific, and it presents as an enhancing mass, which is hypointense on T1 and hyperintense on T2-weighted images, with or without calcifications and cystic changes. It is usually associated with multiple metastatic bone lesions elsewhere. The presence of an abdominal or thoracic mass with multiple other metastatic lesions can point to the diagnosis.
Lymphoma presents as a T1-/T2-weighted isointense or hypointense mass with homogeneous enhancement and lack of calcifications and hemorrhage; the presence of enlarged neck nodes, permeative destruction of bone.
ATRT is highly aggressive with a high incidence of local infiltration; therefore, total excision is not feasible, especially if the tumor involves eloquent areas. Those with CSF dissemination have a poorer prognosis with a median survival of 2.5–3 months. This is especially true for patients less than 3 years of age who are more likely to have dissemination at diagnosis and have a faster rate of progression. Prognosis is dismal, with a median survival of 6 months.
The optimal treatment for ATRT is not well established. The goal of surgery in ATRT is to reduce the tumor bulk, but patients who receive surgery without adjuvant chemotherapy or radiotherapy have a median survival of only 1–3 months after surgery.
| Conclusion|| |
Imaging possibilities of a large heterogeneous posterior fossa mass in a child should include ATRT also. Diagnosis is often established on histopathology; however, raising suspicion is essential; as these tumors tend to have a very aggressive course and a poor outcome.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3]