Ravi Raghavan
Introduction
The classifi cation system of central nervous sys- tem (CNS) tumors has been evolving with newer advances in neuro-imaging, immunohistochemis- try, and molecular genetics. However, a few neo- plasms defy accurate categorization due to their extreme rarity, and poor documentation in the lit- erature. One such emerging group are the tumors with mixed astrocytic and neuronal elements (Cenacchi and Giangaspero 2004 ) , that are diffi - cult to classify, and are generally known as mixed glioneuronal tumors (GNT) (Burger et al. 2002 ; Edgar and Rosenblum 2007 ; McLendon and Provenzale 2002 ) . Besides several cases of low grade GNTs, some malignant forms have been reported (Tihan et al. 1999 ) . It is unclear whether these glioneuronal tumors belong to a single cat- egory or multiple diagnostic entities, but they can- not be grouped with classic gangliogliomas. A few of these low-grade GNTs have been of the
‘rosetted’ variant, the fi rst spinal location of which was documented by Harris and Horoupian ( 2000 ) in an adult, at least to the best of our knowledge.
Subsequently, a few more reports on glioneuronal tumors of the adult spinal cord have been pub- lished (Anan et al . 2009 ; Phi et al . 2009 ) , some with similarities to GNTs of the brain.
In such a narrow fi eld – an area that has still not found a rightful niche in the WHO classifi cation system – an attempt is made here to bring together what we know of mixed GNTs that affect the spi- nal cords of children. This chapter may not be a complete account of this unique group of tumors, because many individual cases may have gone unreported, under-represented (because they were clubbed together with other lesions), or escaped our attention when an on-line search was made.
For the sake of completion, gangliogliomas of the spinal cord will also be briefl y discussed, but the focus will be on these unique pediatric GNTs.
Tentative Classifi cation
As stated earlier, proper categorization of these lesions is still a ‘work in progress’, and anecdotal, waiting to be adequately discussed and debated in
multidisciplinary forums. Based on our own expe- rience of a few cases, and those in the literature, a simple classifi cation system is proposed:
1. Spinal Glioneuronal tumors, Types 1 and 2 2. Spinal Gangliogliomas
3. Other unclassifi ed (i.e., pilocytic astrocytoma- like variants with immunohistochemical evi- dence of neural differentiation etc)
The Type 1 spinal GNT presents with neu- ronal rosettes in a background of glial prolifera- tion, while the Type 2 spinal GNT has mostly immunohistochemical evidence of such mixed neuronal components, and is slightly less distinct from an architectural point of view. Bulk of the documented lesions are of the Type 1 category, and this observation is largely based on their initial presentation and histology, rather than their clinical behavior, which is often that of a low-grade neoplasm, with rare exceptions. Spinal gangliogliomas are essentially no different from their counterparts in the brain, and although rare, have a similar biologic behavior. Lastly, there are the usual unclassifi able tumors that clearly are not of either category.
Illustrative Case Studies (see Table 2.1a )
In our case fi les, we had one each of the two types of spinal GNTs mentioned above (Syed et al.
2006 ) . A reasonable on-line search with ‘spinal’
and ‘glioneuronal’ as keywords revealed four more of such lesions in the English literature, with near-complete documentation for study purposes (Poliani et al. 2009 ; Psarros et al . 2005 ; Rickert et al. 2006 ; Scholz et al . 2009 ; Syed et al . 2006 ) . A few more do exist in abstract form in confer- ence proceedings, or as podium presentations, but were not available for this study. An informal enquiry regarding such lesions amongst neuro- pathologists from nine major centers in the U.S.A., found three or four more cases, but details and adequate follow-up data are still pending on those, as this chapter goes into print. Two additional cases (Table 2.1b ) are mentioned here from a series by Perilongo et al. ( 2002 ) but it is unclear whether these can be classifi ed as glioneuronal tumors.
The following account, therefore, is partly a meta-analysis based on the six published cases of pediatric spinal GNTs, including two of ours (Perilongo et al. 2002 ; Poliani et al. 2009 ; Psarros et al . 2005 ; Rickert et al. 2006 ; Scholz et al . 2009 ; Syed et al . 2006 ) , and attempts to provide some clinic-pathologic correlates that are common to these neoplasms (Table 2.1a , b). The correspon- ding individual reference to each case is not repeated in the following paragraphs, but the reader is directed to the references mentioned above.
Spinal Glio-Neuronal Tumors
Clinical Presentation
The children ranged in age from 15 months to 16 years, with four of six under 5 years of age.
Gender-wise, majority were male children (fi ve of six). In other words, a slightly higher predilec- tion for very young boys is apparent. The pre- senting symptoms and signs mainly included motor weakness of limbs i.e., paresis (3), gait abnormalities or ataxia (2), and intractable back pain (2). Some children also had features of what is best regarded as signs of generalized raised intracranial pressure (cranial nerve palsy, breath- ing diffi culty), myoclonus, and signs of menin- geal involvement, as the disease progressed.
Neuro-imaging is a critical diagnostic tool before such children undergo surgery, and helps to defi ne the nature and extent of the neoplastic process. Basic imaging data were available in all six cases, and displayed an intramedullary elon- gated mass in the thoracic spinal cord in four instances, in the cervical region in one case, and involving both the lower cervical and upper tho- racic cord segments in one case. Contrast enhancement was evident in four of six cases (Fig. 2.1 ), and leptomeningeal involvement seen in two cases. In one case, there was cystic change within the lesion, and in three instances there was a large elongated ‘syrinx’ seen in association (Fig. 2.1 ). The syrinx involved the uninvolved portion of spinal cord (usually proximal to the mass, except in one case, where it extended from C2 to the conus).
The thoracic spinal cord, therefore, generally seems to be the favored location. The contrast enhancement is of interest, because majority of the lesions were not particularly highly vascularized or high-grade in nature. Syrinx formation may not be a specifi c defi ning feature, being an accom- paniment of other intramedullary lesions, but its presence must be a contributor to the symptoma- tology and morbidity.
Pathology
All six cases had mixed glial and neuronal ele- ments in them, with the former represented by a low-cellularity, fi brillary astrocytic background (that was immunoreactive for glial fi brillary acidic protein [GFAP]), punctuated by neuronal cells. The latter usually consisted of clusters of neurocyte-like cells arranged in ‘wreath-like
‘rosettes, variably surrounding fi ne fi brillary neu- ropil. Four of six cases had these ‘rosetted’ struc- tures, and are being designated Type 1 GNTs for ease of description (Fig. 2.2 ). These rosettes stained intensely (both neurocytes and neuropil inside) with neuronal markers such as synapto- physin, neurofi lament protein (NFP), and/or neu- ronal nuclear antigen (NeuN). The other two did not have well-organized rosetted neurons. Instead, they had less distinct rosettes, or small islands of neuropil with immunoreactivity for neuronal antigens mostly within the cells encircling the abortive rosettes (and not within), and are being designated here as Type 2 GNTs (Figs. 2.3 and 2.4 ). These tumors were less structured and more diffuse. A ‘pilocytic astrocytoma’ like appear- ance has been mentioned in two cases, with rare Rosenthal fi bers and eosinophilic granular bodies in one. ‘Oligodendroma-like’ features were men- tioned in one case. Clusters of dysmorphic gan- glia, with fi brosis, and lymphocytic infi ltrates, characteristic of ganglioglioma, were absent.
Mitotic activity was inconspicuous in all, and no striking vascular endothelial proliferation or necrosis was noted.
Cell proliferation indices, as shown on KI-67 (i.e., MIB-1) immunolabeling, was low in four cases (range: 1–3%), and high in two tumors (10% and 15%). One of the cases that had high KI-67 indices initially, recurred with disseminated
Table 2.1a Summary of clinical, pathologic, and radiologic fi ndings in six cases of pediatric mixed glioneuronal tumors
Case Authors Age Gender Clinical presentation Imaging/location Duration Morphology 1 Psarros
et al.
( 2005 )
15 m M Raised pressure symptoms, bilateral 6th nerve palsy
Heterogeneously enhancing mass T8–12; diffuse leptomeningeal enhancement of nerve roots and cauda equina; large syrinx from C1–T8
2–3 weeks initially;
readmitted a week after VP shunt
Fibrillary,
‘oligo-like’.
No ganglion cells.
No rosettes.
No mitoses, pleomorphism, or vascular proliferation 2 Syed et al.
( 2006 )
2 years M Weakness, ataxia Intramedullary, contrast enhancing mass T2–T7 with syrinx from C2 to conus
2 weeks Pilocytic astrocytoma-like, no RFs or EGBs;
early rosettes?
3 Rickert et al.
( 2006 )
16 F Intractable back pain Contrast-enhancing, Intramedullary mass, C7–T2
Months Paucicellular, fi brillary, rosettes present
4 Syed et al.
( 2006 )
8 years F Back pain, weakness lower extremities, Rt sided myoclonus
Cystic mass- thoracic cord
8 months Pilocytic astrocytoma-like, with rare RFs and EGBs, ‘neuronal islands’ with well formed rosettes 5 Scholz
et al.
( 2009 )
5 M Gait disturbance - monoparesis left leg, sensory disturbances bilateral LE
Contrast-enhancing, intramedullary, T10–T12, Huge syrinx C1–T6
NDA
5.1 Paraparesis both LE, Breathing diffi culty
T7–T12 10 months Rosetted GNT
6 Poliani et al.
( 2009 )
15 m M Raised pressure symptoms and signs of meningeal involvement
Intramedullary mass C4–7;
leptomeningeal thickening
Few days Rosetted GNT, Fibrillary and microcystic, rare Rosenthal fi bers
& EGBs;
infi ltrative tendencies
Immunohisto-chemistry Surgery Other treatment Follow-up Patient status Miscellaenous Synaptophysin +, NSE +,
GFAP++, Ki-67 low index
NDA Cisplatin, Tatrazanate, Cytoxan + RT
23 months Tumor and syrinx shrinkage after 16 months. Slight weakness of extremities at 23 months
Synaptophysin +, NFP + , GFAP +, Chromogranin neg, High Ki67 – up to 15%
Partial resection
Eight courses of chemotherapy
57 months Stable
Synaptophysin +, Neu-N +, NFP+, EMA -, Ki67 3%
GTR None 12 months No recurrence after 1 year; persistent left plantar extension paralysis
CGH – Gain 7q21.1-qter, Loss 9p21-pter Synaptophysin +,NFP + ,
NeuN +, GFAP +, Chromogranin neg, low Ki67 – up to 2.8%
GTR in 2 sittings
Chemotherapy induction started 1 year later for possible disseminated disease
12 months Stable with no defi cits, but imaging shows a small recurrence with diffuse meningeal spread
GTR 10 months NDA
Synaptophysin +, GFAP +, Ki67 10%
STR 3 weeks Multiple spinal and brain enhancing lesions; died after 2 months
CGH – Gain 1q, i1q
NSE +, NFP +, NeuN +, HUC/D +, GFAP ++, Ki67 ,1%, Olig-2 neg, p53 equivocal
STR with shunt placement
30 months Recurred 14 months later with meningeal dissemination, lesions over cerebellum, brainstem, hippocampus;
at 22 months; second mass T11–12; died 30 months postop with massive ventricular involvement
Table 2.1b Summary of clinical, pathologic, and radiologic fi ndings in two possible cases of pediatric mixed glion- euronal tumors – unclassifi able
Case Authors Age Gender Clinical presentation Imaging/location Duration 7 Perilongo et al.
( 2002 ) – case #1 of their series
7 M Back pain, mild right hemiparesis, raised IC pressure symptoms
Intramedullary mass C5-6 with diffuse leptomeningeal enhancement, retroclival to cauda equina level
3 months
8 Perilongo et al.
( 2002 ) – case #3 of their series
12 M Raised IC pressure symptoms like headache, vomiting, dysarthria, somnolence, decreased appetite, weight loss
Discrete solid mass, C7–D1, with extensive leptomeningeal and possible parenchymal spread to involve cerebellum, cp angle, occipital cortex, ventricles
1 year
RF Rosenthal fi bers, EGB eosinophilic granular bodies, NDA No data available, GTR gross tumor resection, STR subtotal tumor resection, RT Radiotherapy
metastases and died, but the other was stable after 57 months of follow-up. Clearly, not all were low-grade in behavior, and their outcomes were not predictable based on Ki-67 labeling. From an immunohistochemical viewpoint, the glial por- tion was invariably reactive for GFAP (Fig. 2.3 inset) , and the neuronal components for synapto- physin (Fig. 2.4 ), NFP (Fig. 2.2 inset), and/or NeuN antigens. Neuron specifi c enolase (NSE) was positive in two cases, but chromogranin was not a useful marker.
Two cases were investigated for molecular genetic abnormalities by comparative genomic hybridization (CGH) techniques. It revealed losses on chromosomes 1p and 22q in one case.
The other tumor had loss of entire short, and gain of long arm of chromosome 1, and the authors felt this was consistent with an isochro- mosome 1q (i1q) as the most probable cytoge- netic equivalent of this alteration. The loss of 1p that is common to both cases is of interest, and although too small a number to be signifi cant, suggests a possible common alteration in such tumors. Losses on 1p are extremely uncommon
Fig. 2.1 MRI evidence of a contrast-enhancing mass ( arrow ) in the thoracic cord segment, and an associated intramedullary fl uid-fi lled syrinx
Morphology
Immunohisto-
chemistry Surgery
Other
treatment Follow-up Patient status Miscellaenous No rosettes;
monomorphous cells with round to oval nuclei; no features of Pilocytic astrocytoma incl RFs or EGBs; no mitoses, vascular proliferation or necrosis; confi rmed extensive leptomenin- geal spread at autopsy
Synaptophysin – focal + in aggregates of neoplastic cells, NF- neg, GFAP -scattered + cells, MAP +, Ki-67
<2%
Tumor biopsied
Craniospinal irradiation – 3,960 cGy in 22 fractions
9 months Progressive neurological deterioration 2 months after radiation was started, and died
No rosettes;
monomorphous cells with round to oval nuclei; no features of Pilocytic astrocytoma;
few multinucleate cell present, leptomenin- geal infi ltration present, and no mitoses
Synaptophysin – focal + in aggregates of neoplastic cells, GFAP + in scattered cells, MAP – neg, Ki-67 <1%
Tumor biopsied
Chemotherapy with temoxol- amide – six courses
24 months Child alive 24 months after follow up and clinically stable
Fig. 2.2 Type 1 spinal GNT: Distinct neurocytic rosettes (H&E ×100). The peripheral cells and central neuropil of the rosettes ( arrows ) are positive for NFP antibody (inset ×100). Also present is a background of piloid glial elements
in pilocytic astrocytomas, and may help in dif- ferential diagnosis – a useful point to remember when there is a diagnostic confl ict between
GNTs and PA. Clearly more cases need to be examined before a convincing molecular profi le can be ascertained.
Fig. 2.3 Type 2 spinal GNT: Tumor cells with vague rosette-like structures (H&E ×200) Cells with elongated processes consistent with astrocytes in the background show immunoreactivity for GFAP (inset ×100)
Fig. 2.4 Type 2 spinal GNT: Tumor cells with indistinct rosette-like structures showing immunoreactivity for synaptophysin antibody (×200), mainly within the peripheral neurocytes
Therapy and Outcomes
Surgery with gross total resection was the chosen primary approach in three of fi ve cases, with one needing a subsequent subtotal resection due to
recurrence. Two other cases had partial or subto- tal resections, and the tumor recurred with grave outcomes in one. No data on surgical technique was available in one.
Chemotherapy was offered in two cases post- operatively, and in one instance after the tumor recurred. All three were stable with mild residual defi cits after 1–2 years of follow up.
At least 10–12 months of follow-up data were available in three cases, and for 23, 30, and 57 months in three others, respectively. Four cases with low-grade tumors remained stable on follow-up with mild residual neurologic defi cits, with only one of these showing a minor recurrence with diffuse meningeal spread.
However, in two others, the tumor, although not aggressive at presentation, recurred with multiple enhancing meningeal, spinal, and brain lesions, leading to death within 2 and 22 months respectively.
Spinal Gangliogliomas
Spinal gangliogliomas are relatively more dis- crete lesions with a glial component and a distinct neuronal/ganglionic element consisting of dysmorphic (often binucleate) cell clusters in groups, or interspersed amongst the GFAP- immunoreactive glial cells. Besides immunore- activity for a wide range of commonly used neuronal markers, such as synaptophysin, NSE, NFP, and Neu-N within the ganglionic compo- nent, aberrant reactivity for the CD34 antigen has been seen. Their morphology, clinical pre- sentation, therapy and outcomes are no different from those described in other parts of the CNS, and will not be elaborated here. Several reports are available, and the reader is referred to a major textbook (Burger et al. 2002 ) or short reviews on the topic (Costa et al . 2006 ; Jallo et al . 2004 ) . They are mentioned here for the sake of completion, and to emphasize that they are distinct histologically from spinal GNTs.
They do not show the rosetted neuronal struc- tures as the GNTs, but should be regarded as members of a similar spectrum of neoplasms.
Spinal gangliogliomas are usually low grade tumors with a favorable outcome after resection, unless they harbor more aggressive glial or neural elements (Burger et al. 2002 ; Costa et al.
2006 ; Jallo et al . 2004 ) .
Unclassifi ed (Table 2.1b )
There are many anecdotal case reports of mixed spinal neoplasms in children that pose diagnostic challenges, especially when they present with clinico-radiologic features that are reminiscent of the GNTs described earlier, but do not share all the morphologic fi ndings. For example, in a report of three unusual spinal masses reported by Perilongo et al. ( 2002 ) there are two cases in males aged 7 and 12 years that had mixed cells expressing variable glial and neuronal immuno- reactivity (using antibodies to GFAP, synapto- physin, and MAP2). Interestingly, they had no typical features of pilocytic astrocytomas, accord- ing to the authors. These tumors, in spite of low Ki-67 proliferation indices, spread along the leptomeninges to involve other parts of the CNS.
Tumor was only biopsied, and no resections were attempted. One died 9 months after biopsy (in spite of radiation therapy), and the other survived for 24 months after chemotherapy. Whether these are genuine glioneuronal tumors is uncertain, because the authors did not classifi ed these as GNTs, and the impression is based purely on immunohistochemical grounds. Tumors of a similar nature have also been reported by other authors in abstract form at conferences (personal communication only – full references not available), but are not being discussed in this chapter for want of clinical and pathologic details.
Discussion
This chapter highlights a small set of pediatric spinal cord tumors that have mixed glial and neuronal components. Two types of spinal GNTs have been described here, a more easily identifi able variety with distinct neuronal rosettes (designated ‘Type 1’), and the less common and unstructured variant with mostly immunohis- tochemically defi ned neuronal differentiation (designated ‘Type 2’). It must be stressed that this is a tentative classifi cation used in the con- text of this chapter alone, for ease of description and understanding. This classifi cation will be
reviewed with other experts, after additional cases are examined in the near future. Majority of the spinal GNTs turned out to be low-grade tumors with low cell proliferation (Ki-67) indices, and expressed both glial and neuronal immuno- histochemical markers. However, cell proliferation indices did not accurately predict behavior in all cases. Only two cases had information on molec- ular genetic abnormalities, and although both had losses on chromosome 1p, there are no diagnostic cytogenetic profi les that reliably characterize these neoplasms as yet (Rickert et al . 2006 ; Scholz et al . 2009 ) .
These tumors are distinct from gangliogliomas, and other more common intramedullary spinal cord neoplasms (Burger et al . 2002 ; Costa et al.
2006 ; Edgar and Rosenblum. 2007 ) . Ganglio- gliomas have typically large, dysmorphic ganglia in abnormal clusters, and lack the fi ne rosettes of GNTs (Burger et al . 2002 ; Edgar and Rosenblum 2007 ) . Pilocytic astrocytomas (PA) of the spinal cord, on occasion can express some synapto- physin immunoreactivity, either because of the type of antibody used, due to admixed normal neurons, or sometimes for inexplicable reasons of cross-reactivity (personal observations). They can, however, be distinguished by their discrete and low grade nature, typical biphasic pattern, associated Rosenthal fi bers, eosinophilic granular bodies, and absence of immunoreactivity for other neuronal antigens (Burger et al. 2002 ) . Striking neuronal elements or rosettes are not seen in typi- cal PAs, but the less structured spinal GNTs with- out rosettes (Type 2) can be diffi cult to distinguish from them. Two cases from (Perilongo et al. 2002 ) (see Table 2.1b ) also pose further diffi culties in accurate classifi cation, because they have some clinico-radiologic fi ndings that are reminiscent of spinal GNTS, but lack convincing morphologic features to support it.
Morphologically, these pediatric spinal GNTs have some similarities with the recently described
‘rosetted GNT’ and ‘rosette-forming GNT’ of the fourth ventricle’, tumors typically not reported as primarily involving the spinal cord (Edgar and Rosenblum 2007 ; Komori et al. 1998 ; McLendon and Provenzale 2002 ; Teo et al . 1999 ) . Spinal involvement has been described in at least
one case of cerebral rosetted GNT (Edgar and Rosenblum 2007 ) . Whether the spinal GNTs described here are unique to the cord, or in some way an extension of the same family of GNTS in the brain has not been fully established, but is a distinct possibility. The histogenesis of these curious spinal lesions is uncertain. Although the glial portion is invariably of astrocytic origin, in rare cases, even an oligodendroglioma-like component has been noted (Perry et al. 2002 ; Phi et al . 2009 ) in association with the neurocytic elements. Dual reactivity for glial and neuronal markers have also been observed in the same cells in some instances (personal observations), raising speculations on origins from a pluripotent stem cell.
From a clinical viewpoint, boys, 5 years of age or younger, seem to be predominantly affected by spinal GNTs, with weakness, back pain, and gait issues being the more common presenting symptoms. Signs of raised intracranial pressure, myoclonus, ad cranial nerve palsies have also been reported, but less commonly. The thoracic cord is the usual site of involvement, with con- trast enhancement on imaging, and an associated syrinx seen in many cases. Gross total resection has been possible in a few, and has been effective in stabilizing the patient, although some had chemotherapy and radiation given for recurrence.
Two children had dissemination of their tumor on recurrence, with widespread meningeal and brain involvement, and died (Poliani et al. 2009 ; Scholz et al . 2009 ) , but others had a favorable prognosis and stable disease after treatment.
It is noteworthy that one of the two unclassifi able cases also had a grave outcome (Perilongo et al. 2002 ) .
We had essentially six cases of pediatric spinal GNTs for analysis, because of their rarity and insuffi cient documentation. Two more cases had good data, but could not be classified with certainty as GNTs (Perilongo et al. 2002 ) . A quick informal survey amongst ten neuropathologists in nine large university medical centers within the USA indicated that there may be more such cases that need careful study. By personal communi- cation, it was revealed that at least four to six more cases await formal publication in a peer