Pitfalls in Surgical Neuropathology
Moderators: Dr. Arie Perry and Dr. Richard A. Prayson
Case 2 -
Combined Granular Cell And Small Cell Malignant Astrocytoma
Teresa Ribalta, M.D., Ph.D
Infiltrating, heterogeneous tumor exhibiting two separate components that blend into each other
minimally at the interface: a predominant population (70%) made up of benign-looking, large,
eosinophilic cells, with distinctive granular cytoplasm, and a less extensive component of highly
cellular, uniformly small cells with abundant mitoses. A narrow transition zone of well-differentiated
neoplastic astrocytes interspersed with each cell population is present. Granular cell nuclei are
slightly irregular, sometimes eccentric, and contain small nucleoli. Cytoplasmic granules are small,
non-refringent, PAS-positive and diastase-resistant, and in some cells, are confined to the peripheral
area of cytoplasm. In the small cell areas, a well-developed focal capillary network, occasional
perinuclear haloes, and psammoma-type calcifications may suggest oligodendroglial tumor. EM: Abundant lysosomes (dense bodies, autophagic vacuoles) and bundles of
intermediate filaments in granular cells. IHC: GFAP is strongly positive in the atypical
astrocytes of the border zone, focally positive in the small cells, and weakly to moderately positive in
granular cells; CD68, a-1-antitrypsin, a-1-antiquimotrypsin, and ubiquitin only positive in granular
cells; MIB-1 LI ranging from 50% in small cells to 13% in granular cells. EGFR overexpression and
p53-negative staining in both tumor areas. FISH: intact 1p/19q and EGFR amplification in both
Case 2 - Figure 1
Taken separately, the granular cells simulate a reactive condition or a benign granular cell tumor.
However, the surgical specimen in our case clearly revealed a neoplastic process, so the main
differential diagnosis is that of an anaplastic oligodendroglioma (WHO grade III) with a granular cell
component or macrophage infiltration.
An intact 1p/19q and EGFR overexpression do not exclude the possibility of an oligodendroglial tumor,
since the codeletion is present in only 50-70% of anaplastic oligodendrogliomas and EGFR overexpression
is observed in about 50% of oligodendroglial tumors; however, genetic amplification of EGFR is not a
feature in these tumors (Reifenberger 1996). Instead, EGFR amplification is present in about half of
glioblastomas (GBM), particularly in the small cell variant. In our case, demonstration of EGFR
amplification without deletion of chromosomes 1p and 19q is highly consistent with GBM. EGFR
amplification was also clearly present in the granular cells, thus confirming their neoplastic nature and
suggesting a common genetic origin with the small cell GBM component.
Histologic Variants of Glioblastoma
As is well known, the histologic and cytologic spectrum that GBM may display is among the widest in
neuro-oncology. The tumor cells can vary from poorly differentiated small cells to spindle, round or
pleomorphic cells to multinucleated giant cells. A significant intra- and intertumoral morphologic
heterogeneity is also characteristic. However, there are a number of GBM variants with peculiar
morphologic features which are less frequently encountered and can cause confusion with other tumor types
or non-neoplastic lesions (Fuller 2004). Some of these variants are recognized by the current WHO 2000
classification of CNS tumors (Kleihues 2000), while others have been characterized more recently. The
distinctive pathologic features, differential diagnoses, and diagnostic markers of GBM variants are
summarized in the Table. In the present case, a recently recognized small cell variant was seen in
combination with a granular cell astrocytoma, a rare and still not fully characterized entity. Both
variants share a deceptively bland histology and a poor prognosis, and should not be misdiagnosed as less
Small Cell Astrocytoma/Glioblastoma Variant
GBMs usually contain variable proportions of small, primitive cells in appearance, with markedly
hyperchromatic nuclei; however, the small cell GBM variant, as outlined recently (Burger 2001), has been
defined as a highly cellular, cytologically monotonous neoplasm with bland nuclei and a brisk mitotic
activity, that can closely mimic anaplastic oligodendroglioma. The small cell phenotype is commonly
associated with EGFR amplification and it is considered an important component of primary GBMs. Given
the improved prognosis and therapeutic responsiveness of patients with oligodendroglial tumors,
particularly for those with the combined deletion of chromosomes 1p and 19q, the distinction between the
two entities is crucial. Recently, Perry et al. (2004) have further characterized this variant in a
clinicopathologic and genetic study of 71 small cell malignant astrocytomas, which included 33% of tumors
that, as in our case, were classified as anaplastic astrocytoma (Grade III) using WHO criteria.
Interestingly, these anaplastic tumors progressed rapidly, with mortality rates that were
indistinguishable from the grade IV astrocytomas. Therefore, small cell astrocytoma is an aggressive
histologic variant that behaves like primary GBM, even in the absence of microvascular proliferation and
necrosis. Grading following the current WHO criteria is problematic but as Perry suggests, such
neoplasms are GBM molecularly, although not yet histologically. None of the 71 small cell astrocytomas
in his series had 1p/19q codeletions, whereas EGFR amplification and 10q deletions were present in 69%
and 97% of tumors, respectively. Small cell GBMs expressed EGFR (83%) and EGFR-vIII (50%) more commonly
than non-small cell GBMs (35% and 21%, respectively).
Granular Cell Astrocytoma/Glioblastoma
Granular cell astrocytoma (GCA) is an uncommon variant of infiltrative glioma, characterized
histopathologically by a prominent population of bland, granular astrocytoma cells and clinically by aggressive behavior. Granular cells are large, round,
with eccentric nuclei, and are packed with eosinophilic, PAS-positive and diastase-resistant granules.
Since upon initial inspection, the granular cells resemble large macrophages, GCA may be mistaken for
non-neoplastic lesions, such as evolving infarct and demyelinating disease (Zagzag 1993), especially
in small biopsy specimens. GCA shares the cytologic features with granular cell tumors of pituitary
stalk and elsewhere in the body. However, despite the morphologic resemblance, granular cell tumors seem
to be biologically heterogeneous (Rickert 1997).
The histopathologic spectrum and biological behavior of GCAs has been recently studied by Brat et al
(2002) in 22 cases, the largest series to date. Of the 22 cases (age range 29-75 y.o.; 17 men), 6 were
pure GCA and the rest showed transition to a more conventional astrocytoma. None of the 22 GCAs showed a
combined small cell glioma component as in our case. Focal GFAP staining of the granular cells was seen
in all but one tumor. The majority of cases were also immunoreactive for S-100 protein, KP-1, ubiquitin,
and EMA. In all cases, MIB-1 labeling index was significantly lower in the granular cell component than
in the conventional astrocytoma cells. Following the WHO 2000 criteria, four tumors were classified
grade II, 7 were grade III, and 11 were grade IV. However, the vast majority of tumors progressed to
death in less than one year, independently of the tumor grade. The cause of this apparent aggressiveness
of GCA is currently unknown. It has been suggested, by analogy to gemistocytic astrocytomas, that
non-proliferative granular cells, which reflect severe abnormalities in cell cycle regulation, could be a
morphologic marker of poor prognosis in diffuse astrocytoma (Chorny 2000). No genetic alterations
specific for GCA were found in a subgroup of 11 tumors in Brat's series (Castellano-Sanchez 2003). In
contrast with our case, EGFR amplification was not observed in any tumor. Either, no specific
chromosomal imbalances were observed in another series of 7 cases studied by CGH (Rickert 2002).
Instead, a high frequency of allelic loss, especially on 9p and 10q, occurred in most of the cases,
including low grade lesions, which could confer aggressive growth potential to these tumors.
Although the distinction from reactive macrophages can be difficult in small biopsy specimens,
a number of traits are useful in recognizing the neoplastic character of the granular cells in the GCA
variant: granular tumor cells are significantly larger than macrophages, show nuclear
atypia or at least nuclear enlargement, and, often, prominent nucleoli. The cytoplasmic granules
are smaller and more uniform than those of macrophages. In some cells, a circular disposition of
granules at the cell periphery produces a "targetoid" appearance. The granular change is due to
accumulation of lysosomes in the cytoplasm and it is currently considered a degenerative phenomenon that
can occur in a wide variety of tumor types (Geddes 1996). In addition to astrocytic neoplasms, granular
cells have been described in other glial and nonglial CNS tumors (Giangaspero 1999). Since CD68 (KP-1)
is an indiscriminant lysosomal marker (Hulette 1992), it is not useful for distinguishing GCA from
macrophage infiltration. GFAP and S-100 proteinreactivities coupled
with the above mentioned morphologic features are strong evidence of glial neoplasia. In the majority of
specimens, a close examination will disclose the presence, at least focally, of conventional infiltrating
atypical astrocytes, obscured by the granular cell component. Another mimic of GCA cells is eosinophilic
granular bodies (EGBs), which are considered a useful diagnostic finding to distinguish pilocytic
astrocytoma and other low-grade astrocytic lesions from malignant gliomas, although an occasional EGB may
be observed in GBM. EGB granules are refringent, irregular in size and usually are seen associated with
This case was seen in consultation and, according the information provided by the referring
pathologist, the patient was treated with postoperative irradiation (60 Gy) and chemotherapy with
carmustine (BCNU), and she is alive and without clinical or radiological evidence of recurrence 16 months
Both small cell and granular cell GBM variants, which were encountered together in this unique tumor,
are highly aggressive neoplasms with morphologic features that overlap with anaplastic oligodendroglioma
and benign conditions, respectively. Given the greatly different treatment and survival of these groups
of patients, accurate diagnosis is critical. Awareness of these variants and careful assessment of
conventional light microscopy, along with ancillary techniques, including immunohistochemistry,
cytogenetics, and in some cases electron microscopy, are keys to avoid misdiagnosis in uncommon GBM
Table 1 - Morphologic variants of glioblastoma (GBM). Pathologic features,
differential diagnoses, and helpful diagnostic markers
|GBM Variant ||Distinguishing Pathologic Features ||Differential Diagnoses ||Diagnostic Markers|
|Granular cell ||Large granular cells, peripheral rims of eosinophilic granularity, nuclear atypia ||Infarct, multiple sclerosis, progressive multifocal leukoencephalopathy, benign granular cell tumors ||Nuclear atypia, GFAP, S-100 protein, electron microscopy|
|Small cell ||Small glial cells, sometimes with bland nuclei ||Anaplastic oligodendroglioma, low-grade glioma (rarely PNET, lymphoma, carcinoma, melanoma) ||Intact 1p/19q, |
EGFR amplification (70%),
10q deletion (>95%)
|Giant cell ||Relatively circunscribed tumor, predominance of bizarre, multinucleated giant cells ||Pleomorphic xanthoastrocytoma ||Mitoses, microvascular proliferation, necrosis, p53 mutations (>75%)|
|Spindle cell ||Bipolar, fusiform cells ||Sarcoma, gliosarcoma, malignant meningioma, carcinoma ||GFAP, S-100 protein|
|Gliosarcoma ||Biphasic tissue pattern (alternating areas of GBM and sarcoma), metaplastic epithelium, bone, muscle, or cartilage ||GBM invading meninges, spindle cell GBM, fibrosarcoma ||GFAP, reticulin, actin|
|Adenoid ||Cohesive small epithelial cells, glandular structures ||Carcinoma ||GFAP|
|Epithelioid ||Superficial, relatively circunscribed tumor, cohesive rounded cells without processes ||Amelanotic melanoma, carcinoma, meningioma ||GFAP|
|Lipid-Rich ||Relatively circunscribed tumor, cohesive epithelioid cells with foamy cytoplasm ||Balloon cell melanoma, pleomorphic xanthoastrocytoma ||GFAP, reticulin|
|Myxoid ||Striking myxoid background ||Sarcoma, chordoid glioma, myxoid meningioma, other myxoid tumors ||Mitoses, microvascular proliferation, GFAP|
|Inflammatory ||Prominent neutrophil or macrophage infiltration ||Abscess and other inflammatory disorders, infarct, demyelinating disease ||Atypical astrocytes, GFAP|
- Brat DJ et al. Infiltrative astrocytomas with granular cell features (granular cell astrocytomas). A study of histopathologic features, grading, and outcome. Am J Surgical Pathol 2002; 26:750-57.
- Burger PC et al. Small Cell Architecture. A Histological Equivalent of EGFR Amplification in glioblastoma Multiforme? J Neuropath Exp Neurol 2001;60:1099-1104.
- Castellano-Sanchez AA et al. Granular cell astrocytomas show a high frequency of allelic loss but are not a genetically defined subset. Brain Pathol 2003;13:185-94.
- Chorny JA et al. Cerebral granular cell astrocytomas: a MIB-1, bcl-2, and telomerase study. Clin Neuropathol 2000;19:170-9.
- Fuller GN. Glioblastoma (Epithelioid Variant). Specialty Conferences, Neuropathology, Case 5, 93rd Annual Meeting of the USCAP, Vancouver , BC , Canada , March 6-12, 2004
- Geddes JF et al. Granular cell change in astrocytic tumors. Am J Surg Pathol 1996;20:55-63.
- Giangaspero F et al. Oncocytic and granular cell neoplasms of the central nervous system and pituitary gland. Semin Diagn Pathol 1999; 16:91-7.
- Hulette CM et al. Macrophage markers in diagnostic neuropathology. Am J Surg Pathol 1992;16:493-99.
- Kleihues P et al. Glioblastoma. In Kleihues P and Cavenee WK, eds., World Health Organization Classification of Tumours: Pathology and Genetics of Tumors of the Nervous System. Lyon: IARC Press, 2000, pp. 29-39.
- Perry A et al. Small cell astrocytoma: an aggressive variant that is clinicopathologically and genetically distinct from anaplastic oligodendroglioma. Cancer. 2004;15:2318-26.
- Reifenberger J et al. Epidermal growth factor receptor expression in oligodendroglial tumors. Am J Pathol 1996;149:29–35.
- Rickert C et al. Morphological and immunohistochemical characterization of granular cells in non-hypophiseal tumors of the central nervous system. Histopathology 1997;30:464-71.
- Rickert C et al. Genetic characterisation of granular cell tumours. Acta Neuropathol 2002;103:309-12.
- Zagzag D et al. Demyelinating disease versus tumor in surgical neuropathology: clues to the correct pathological diagnosis. Am J Surg Pathol 1993;17:537-45.