A 33 year-old woman with a mass that extends from the frontal lobe into the nasal sinus.

Bobbie C. Sutton, M.D., Cheng Z. Liu, M.D., Ph.D., Kar-Ming Fung, M.D., Ph.D., Terrance Dunn, Ph.D. Last update: April 1, 2007.

Department of Pathology, University of Oklahoma Health Science Center, Oklahoma City, Oklahoma

Clinical information: The patient was a 35 year-old woman who presented with sinus congestions, loss of smell, and headache. On MRI scan, an non-enhancong, intra-axial mass that extended from the frontal lobe through the cribiform plate to the nasal sinus. The bulk of tumor is in the frontal lobe. A biopsy of the nasal component was performed and the followings are the representative images from the biopsy material:

Click thumbnails to see pictures. (GFAP: glial fibrillary acidic protein; NFP- neurofilament proteins; Syn: synaptophysin)

At scanning magnification, part of the biopsy material appears polypoid fragments covered by respiratory type epithelium (arrow in Panel A) and the tumor is essentially a densely packed, cellular tumor with clear cell features at scanning magnicfication. On low magnification, there tumor contains some spindle cell area but a substantial amount of the tissue has a clear cell component (arrow in Panel B). Even in the spindle areas, some clear cells are present (Panel C). The spindle cell areas also have poor cytoplasmic membrane and give a glial tissue appearance. The clear cell areas are composed of solid sheets of small, polygonal, monotonous cells with a delicate but rich vascular network (Panel D). On high magnification, the tumor cells lacks anaplastic features. Mitotic figures are not readily seen. Neither endothelial proliferation nor necrosis is present (Panel E and F).

On immunohistochemistry, some cells in the spindle cell area are positive for GFAP (Panel G). Except for some entrapped cytoplasmic processes, the clear cells are negative for GFAP (Panel H). Immunohistochemistry for neurofilament proteins yields a similar staining pattern (Panel I). Immunohistochemistry for synaptophysin demonstrate strong positive staining (Panel J).

Fluorescent in situ hybridization (FISH) is performed and demonstrated deletion of chromosome 1p and 19q (Panel K). Oligodendroglioma tumor cell nuclei stained with the Vysis^® LSI^®1p36/1q25 Dual-Color Probe Set and viewed by fluorescent microscopy. Two distinct hybridization signal colors are seen in these interphase nuclei: two green signals but only one orange signal in cells showing a 1p deletion. Normal interphase nuclei show two copies of both probe signals.

Technical details on Determination of 1p 19q Deletions by Fluorescent in situ Hybridization (FISH).

The Vysis^® LSI^®1p36/1q25 and LSI 19q13/19p13 Dual-Color Probe Set (Cat#32- 231004) consists of two separate probe mixtures each containing two DNA probes. The 1p36 probe is labeled with SpectrumOrange^TM and contains sequences that extend from near SHGC57243 locus, through the TP73 and EGFL3 genes and ends proximally at a point telomeric to the EGFL3 locus. The 1q25 probe is labeled with SpectrumGreen^TM and contains sequences that extend from a point telomeric to the WI-6848 locus, through the ABL2 and ANGPTL1 genes and ends proximally near the SHGC-1322 locus. The 19p13 probe is labeled with SpectrumGreen^TM and contains sequences that extend from a point centromeric to the MAN2B1 locus, through MAN2B1, ZNF443 and ZNF44 genes and ends proximally at a point telomeric to the ZNF44 locus. The 19q13 probe is labeled with SpectrumOrange^TM and contains sequences that extend from a point telomeric to the CRX locus, through the CRX, GLTSCR2 and GLTSCR1 genes and ends proximally at a point centromeric to the GLTSCR1 locus.

TheVysis^® LSI^®1p36/1q25 Dual-Color Probe Set will generally produce four distinct hybridization signals of two different colors in interphase nuclei: two green and two orange. This reflects the presence of two intact copies of 1p and 1q. In abnormal interphase nuclei with a 1p deletion generally two green signals and one orange signal (one being deleted) will be present. See Figure 1. Similar results are obtained with the LSI 19q13/19p13 Dual-Color Probe Set. Different patterns may be generated due to truncation of cell nuclei during sectioning of paraffin embedded tissues. Aneuploidies of chromosomes 1 or 19, which are frequent in gliomas, may also be detected with these probes.

This is an unusual case. Other than meningiomas arising at the cranial base, primary brain tumors do not typically invade the cranial bone and this is particularly true for glial neoplasm. The current tumor is clearly not a meningioma. This raises a question whether this is a primary tumor that arises in the nasal cavity that invades into the brain or a brain tumor that invades through the cribiform plate. Histologically, this tumor does not have feature of a carcinoma, sarcoma, lymphoma or melanoma. The histologic features, particularly the strong immunohistochemical reactivity for synaptophysin is suggestive of a well-differentiated neuroblastoma. This tumor, however, does not have small cell component which is a little uncommon in olfactory neuroblastoma. The possibility of a synaptophysin positive, and possibly an oligodendroglioma with neurocytic differentiation must be serioiusly entertained. As deletion of chromosome 1p and 19q is demonstrated by FISH and the fact that the bulk of the tumor is in the brain, the pathologic features are most consistent with an oligodendroglioma arising in the frontal lobe that invades through the cribiform plate. Although positive for synaptophysin, there is no morphologic evidence of neuronal differentiation to support a diagnosis of oligodendroglioma with neurocytic differentiation.

Although the clinical and imaging characteristics of our case suggest an esthesioneuroblastoma (olfactory neuroblastoma) but the extensive frontal lobe involvement is unusual. Esthesioneuorblastomas can have a range of differentiation Histologically, they can range from a highly cellular, medulloblastoma or neuroblastoma like tumor to a moderately cellular, glioma like tumor. Synaptophysin is typically positive in esthesioneuorblastomas but some oligodendrogliomas are also express synaptophysin. In our case, the demonstration of chromosome 1p and 19q deletion confirmed the oligodendroglial lineage of this tumor. The followings is the according to the Hyams grading system:

Features	Grade 1	Grade 2	Grade 3	Grade 4
Cytoarchitecture	Lobular	Lobular	± Lobular	± Lobular
Mitotic rate	0	Low	High	High
Nuclear pleomorphism	None	Slight	Moderate	Marked
Fibrillary background	Prominent	Present	Slight	None
Rosettes	± Homer-Wright	± Homer-Wright	Flexner-Wintersteiner	None
Necrosis	None	None	Mild	Frequent

Hyams VJ, Batsakis JG, Michaels L. Tumors of the upper respiratory tract and ear. Atlas of Tumor Pathology, 2nd series, Fascicle 25. Armed Forces Institute of Pathology, Washington DC, 1988; 240-248.

There are no specific immunohistochemical markers for the diagnosis of oligodendroglial tumors. Differentiation of these tumors from astrocytic and other tumors can be difficult in some cases. The identification of chromosome 1p 19q deletion in oligodendroglioma is particularly helpful in resolving this dilemma as well demonstrated in the present case.

Gliomas are the most common primary malignancies of the central nervous system in adult. Histologically, most of these tumors have phenotypic properties of astrocytic (astrocytomas), oligodendroglial (oligodendrogliomas), or ependymal differentiation (ependymomas). Some gliomas have mixed glial differentiation. A small number of them are of uncertain origin. In the WHO classification, oligodendrogliomas are of WHO grade II, anaplastic oligodendrogliomas are WHO grade III. Mixed oligoastrocytomas (MOAs) are WHO grade II and anaplastic MOA are WHO grade III. This classification is based predominantly on morphologic features ¹. With the advancement of our understanding on the molecular pathology of these tumors, more and more molecular markers are now available for the evaluation of these tumors ^2,

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Oligodendrogliomas constitute about 10 to 20% of all primary gliomas with most of them found in the middle aged people. Around 60% of all cases occur in between 40 to 70 years old. The peak incidence occurs at the 5th and 6th decades. They occur almost exclusively in the cerebral hemispheres with the frontal lobe as the most common site. In one study, tumors with oligodendrogliaoma component comprise about 25% of diffuse gliomas ⁴. While oligodendrogliomas is an indolent and slow-growing tumor, anaplastic oligodendrogliomas behave in a more aggressive fashion. While distinction of WHO grade II and grade III oligodendorogliomas is not particularly difficult in many cases, a controversial gray zone with considerable inter-observer variability exist.

Macroscopically, oligodendrogliomas infiltrate the cortex diffusely which lead to expansion and an “hypertrophic” appearance of the cortex. In the underlying white matter, large and small mucinous cysts are present. Calcifications within the tumor and in surround tissue are common and a good diagnostic hint on imaging. When the tumor breaks through the leptomeninges, it may form large lumps that project beyond the surface like bluish red mushrooms and tend to adhere to the dura and may be mistaken as meningiomas. Invasion of the leptomeninges is not unusual. Bone erosion has been described but is rather uncommon.

Microscopically, the classic “fried-egg” appearance with a delicate “chicken wire” like vascular network is a faithful and practical description of oligodendrogliomas (WHO grade II). In essence, the classic examples are composed of solid sheets of polygonal clear cells with distinct cell border. The nuclei are rather monotonous, small, bland, round, and without prominent nucleoli. A rich vascular network with delicate, thin walled blood vessels is embedded among tumor cells. It should note that the clearing of cytoplasm is resulted from acute swelling after the tumor is removed from the brain or as post mortem changes. Therefore, it is not an invariable finding, in particular, the clearing is not seen in frozen section fixed with methanol or alcohol. Mitosis is not readily or scant at the most. Calcifications are quite common and entrapped neurons are also classic features. Perineuronal satellitosis in the surrounding cerebral is a common feature. Numerous small microcysts with mucoid content can be seen in some tumors and as a result, these tumors appear as mucoid, paste like tissue on gross examination. The border with the surrounding tissue can be quite discrete in comparison to diffuse astrocytomas. Other pattern and cytologic features other than the “fried-egg” and mucoid-microcystic pattern can co-exists. These include features such as the rhythmic palisading pattern, perivascular papillary pattern, and minigemistocytic cells. [Images of oligodendrogliomas]

Anaplastic oligodendrogliomas (WHO grade III) maintain the basic features of oligodendrogliomas (WHO grade II). There is a decrease in nuclear cytoplasmic ratio. In addition to the increased pleomorphism and hyperchromatasia, the tumor cells tend to have less clearing. Brisk mitotic activity can usually be demonstrated. Small necrosis and endothelial proliferation can be present. The distinction between the two entities, however, is not clear cut. A subset of glioblastoma also have substantial oligodendroglial features and they have a better prognosis than the conventional glioblastoma ⁵.

The majority of oligodendrogliomas show allelic loss of the short arm of chromosome 1 (1p). Sixty to 70% of oligodendrogliomas are characterized by a combined loss of the entire short arm of chromosome 1 and the long arm of chromosome 19, i.e., 1p/19q co-deletion ^{6,

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13}. The 1p/19q codeletion is most commonly encountered in classic oligodendrogliomas. Other oligodendrogliomas show 19q loss only. “Astrocytomas” that recur after more than 10 years are often the result of misclassification at original pathologic review; re-review generally demonstrates oligodendroglial rather than astrocytic features and FISH often reveals combined 1p and 19q deletions. FISH is a useful technique in the study of paraffin embedded tissue sections ^3,

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The following table summarizes FISH results for 1p/19q status in 103 gliomas ³.

Diagnosis	-1p and -19q	+1p or +19q	-19q only

Oligodendroglioma II-IV (n=47)	63%	17%	2%
MOA or Glioma NOS II-IV (n=48)	17%	48%	13%
Astrocytoma III-IV (n=8)	0%	25%	25%

Recently, the importance of accurate diagnosis of oligodendrogliomas has become apparent with the observation that many anaplastic oligodendrogliomas, unlike ependymomas and astrocytomas, are particularly sensitive to chemotherapy. The success of PCV (procarbazine, lomustine (CCNU) and vincristine) regimen in the treatment of oligodendrogliomas is now well-established ^6,

12. Favorable responses appear to be restricted to high-grade (Anaplastic) oligodendrogliomas (WHO Grade III) with specific cytogenetic changes, especially chromosome 1p loss. Several studies have also documented that 1p/19q co-deletion is an independent predictor of chemosensitivity and radiosensitivity. Such deletions also correlate with longer recurrence-free survival in pure oligodenrogliomas irrespective of grade. The mechanism of this enhanced response is poorly understood. In contrast, when these deletions are found in astrocytomas or MOAs, they are apparently not associated with favorable prognosis. Glioblastoma with oligodendroglial features show more frequently 19q deletion only but deletion of 1p or combined 1p19q is relatively infrequent in these tumors ⁵.

Patients with malignant glioma, whose tumor histology demonstrates pure oligodendrogliomal or mixed oligoastrocytomas features, can benefit from molecular analysis of the tumor for 1p and 19q deletions, by using either PCR or FISH methods. Patients with such tumors demonstrating 1p and/or 19q deletion would normally be expected to respond favorably to standard chemotherapy and thus may be spared the adverse effects of radiotherapy to the brain.

Cytoarchitecture

Oligodendroglioma II-IV (n=47)