DECEMBER 2006: 31‐YEAR‐OLD WOMAN WITH HEMIPARESIS

CLINICAL HISTORY

A 31‐year‐old, previously healthy woman experienced a new‐onset generalized seizure with subsequent right‐sided weakness in the 37th week of her pregnancy. She also reported slowly increasing weakness in her right leg over the past several months. Neurologic examination on admission revealed a young woman who was somnolent but easily arousable. She demonstrated a moderate right‐sided hemiparesis and a mild right‐sided facial droop was also present. Babinski sign was present bilaterally, and fundic exam revealed papilledema bilaterally.

Initial evaluation with cranial CT scans demonstrated a large left parasagittal mass with midline shift. MRI of the brain revealed a robustly enhancing 7.8 × 4.6 cm left frontal lobe mass lesion adjacent to the falx cerebri (Figure 1). It effaced the left lateral ventricle and was associated with significant mass effect resulting in 1.5 cm of midline shift. T2 sequences revealed marked vasogenic edema extending throughout most of the left cerebral hemisphere.

Figure 1.

On the day following admission she was brought to the operating room by the obstetrics service for cesarean section under general anesthesia. This was performed without complication to mother or child. Approximately 24 h postoperatively the patient developed recurrent generalized seizure activity and became progressively lethargic and ultimately comatose with non‐reactive pupils. This decline in her neurologic exam was accompanied by persistent hypertension and bradycardia suggestive of increased ICP. Repeat imaging revealed only continued mass effect and midline shift from the tumor without evidence of hemorrhage. She was treated aggressively with mannitol and high‐dose glucocorticoids to which she had a dramatic clinical response—she was once again awake, conversant and able to follow commands.

Six days post cesarean section the patient remained clinically stable on mannitol and steroids and was taken to the operating room for craniotomy. Intra‐operatively, the tumor had the gross appearance and consistency of a meningioma. It was found to arise from the falx cerebri, from which most of its blood supply originated. A gross‐total resection was achieved. By 6 weeks postoperatively the patient was doing extremely well and had made a complete neurologic recovery.

PATHOLOGY

H&E‐stained sections revealed a myxoid, spindle cell tumor with hypocellular and hypercellular areas. There was no evidence of mitoses, necrosis, inflammation, or granulomas (Figures 2 and 3a). One focus with a vague meningothelial pattern and a nuclear pseudoinclusion was found (Figure 3b). The tumor stained diffusely with Alcian blue, pH 2.5, (Figure 3c) and PAS. No keloid‐like collagen or slit‐like vascular pattern was found, and CD34 immunohistochemistry was negative. A reticulin stain demonstrated scattered reticulin fibers within the myxoid extracellular material. Tumor cells exhibited no significant epithelial membrane antigen (EMA) immunostaining at a dilution of 1:400 but did demonstrate immunoreactivity at dilutions of 1:100 and 1:40. There was no AE1/AE3 (repeated), CAM 5.2, smooth muscle actin, muscle‐specific actin, myogenin, CD34, glial fibrillary acidic protein, or S‐100 protein immunoreactivity. CD68 immunohistochemistry demonstrated only rare monocytes. Electron microscopic analysis revealed external lamina around some cells and showed evidence of primitive cell junctions (Figure 3d).

Figure 2.

Figure 3.

DIAGNOSIS

Myxoid meningioma.

DISCUSSION

The metaplastic variants of meningioma are an interesting subgroup that highlight the broad histological repertoire of these neoplasms (8). Of these variants, myxoid meningioma poses a particularly difficult diagnostic challenge. These lesions do not display the usual histological features of more typical meningiomas and have abundant mucoid stroma that mimics other myxoid tumors. Currently, the diagnosis of myxoid meningioma is contingent on: (i) recognition that the tumor arises from the leptomeninges, (ii) discovery of obscure meningioma histology, (iii) extensive Alcian blue staining, (iv) identification of tight junctions and basal lamina, and (v) exclusion of other myxoid tumors 2, 3, 4, 5, 7. Notable among the histologic features of myxoid meningiomas is that they demonstrate little or no immunoreactivity to recommended dilutions of EMA. In addition, immunostaining for other cytokeratins, smooth muscle actin, muscle‐specific actin, and S‐100 protein are all generally negative.

The myxoid variant of meningioma must be differentiated from both other dural‐based lesions that radiographically mimic meningiomas and other myxoid spindle cell neoplasms including schwannomas, fibromyxomas or fibroxanthomas of the dura 6, 8. For instance, if located near cranial nerves, the circumscription, combined spindle cell and myxoid histologic patterns, variable S‐100 immunoreactivity, lack of EMA immunoreactivity, and ultrastructural evidence of basal lamina might suggest a diagnosis of schwannoma. Myxoid meningiomas must also be differentiated from myxoid solitary fibrous tumors (SFT) of the falx or cerebellopontine angle, which present in the same age group as meningiomas (mean age = 57 years) and occur more commonly in females (5:2, F : M ratio) (6). In theory, nerve sheath myxomas (neurothekomas) might be considered in the differential diagnosis but don’t usually occur at this site and rarely develop in this age group (9). Similarly, myxoid liposarcomas may rarely metastasize to the dura but display notably different histologic features (1). Thus, recognition of myxoid variants requires use of all of the histologic tools available to the pathologist.

Our experience suggests that these tumors grow like other metaplastic variants, with similar recurrence rates. Nonetheless, because of the paucity of reported cases and long‐term follow‐up, the behavior of this meningioma variant has yet to be established.

CASE OF THE MONTH: ABSTRACTS

October 2006. Astroblastoma is a rare tumor of glial lineage usually occurring in young adults and involving the supratentorial compartment. Brain stem and cerebellar examples are uncommon. We report a 37‐year‐old patient who presented with 2‐month history of headache and balance impairment. Pre‐operative MR scans showed a cystic, contrast‐enhanced lesion involving the cortex of the left cerebellar hemisphere. Histologically, the tumor showed compressive margins, appeared rich in vessels and featured compact architecture with no fibrillary background. It contained perivascular pseudorosettes composed of columnar cells with short cytoplasmic processes and eccentric nuclei. Mitoses were rare and necrosis was absent. Tumor cells expressed GFAP, S‐100 protein and NSE. Immunoreactions for cytokeratin CAM5.2, cytokeratins AE1/AE3, smooth muscle actin, CD31, EMA, chromogranin and synaptophysin were negative. Electron microscopy showed capillaries with grossly thickened basal lamina. Cell junctions of tumor cells were primitive and intermediate. There were no intracytoplasmic lumina, ciliary bodies and microvilli. A diagnosis of low grade astroblastoma was made. Low grade astroblastoma has an excellent long term survival when gross totally resection. High grade examples have an unfavorable outcome, often similar to glioblastoma. Mitoses, cellular atypia and microvascular proliferation appear to be poor prognostic indicators.

November 2006. A 39‐year‐old man presented to the hospital following new‐onset seizure activity. A CT scan of the head revealed a left temporoparietal mass with prominent surrounding edema, which had a rim‐enhancing wall following administration of contrast media. On the basis of the clinical and neuro‐imaging findings, a brain tumor was suspected, and was considered to be most consistent with a high‐grade glioma. At the time of surgical resection, the mass was found to have a firm and rubbery consistency, with a well‐demarcated plane of resection between it and the surrounding brain parenchyma. Microscopic examination revealed features characteristic of an intracerebral tuberculoma, with a central area of necrotic tissue surrounded by a zone of granulomatous inflammation. Centrally situated giant cells or small areas of caseous necrosis were often found within individual granulomata. Microorganisms were not identified with special stains, including those for acid‐fast bacilli and fungi. However, Mycobacterium tuberculosis complex was isolated in cultures of tissue from the mass. While intracranial tuberculomas remain relatively common in developing nations, they are now rare in industrialized countries. The diagnosis may be difficult to make in the absence of extracranial tuberculosis, and a brain biopsy may be indicated. A definitive diagnosis can be made in this situation following demonstration of acid‐fast microorganisms by stain, culture, immunohistochemistry, or PCR.

December 2006. This 31‐year‐old woman presented with a new‐onset generalized seizure and right‐sided hemiparesis in the 37th week of her pregnancy. Magnetic resonance imaging (MRI) of the brain revealed an 8 × 4.5 cm enhancing left parasagittal mass with marked cerebral edema and mass effect. The baby was delivered via cesarean section under general anesthesia without complication. Postoperatively the woman became progressively lethargic with associated clinical findings of increased intracranial pressure (ICP). She was stabilized and brought to the operating room for craniotomy and gross‐total resection of the tumor. Pathologic examination including immunohistochemistry and electron microscopy was consistent with a myxoid meningioma. Myxoid meningiomas represent a rare variant of meningioma whose diagnosis is often overlooked or mistaken for other myxoid tumors. Careful evaluation of preoperative images, awareness of the relationships between the mass, leptomeninges and surrounding brain at the time of surgery, and thorough histologic characterization, are essential for accurate diagnosis of this rare tumor.