Prepared by James M. Larner, MD, and Charles H. Shelton III, MD, Department of Therapeutic Radiology and Oncology; Mark E. Shaffrey, MD, Department of Neurosurgery; Steven A. Newman, MD, Department of Opthamology; and C. Douglas Phillips, MD, Department of Radiology, University of Virginia Medical Center, Charlottesville, VA. Dr. Phillips is also a member of the editorial advisory board of this journal.

CASE SUMMARY:

A 44-year-old left-handed woman presented with a history of headache. Neurological examination revealed left hand incoordination. Imaging on a 1.5-T imager (Magnetom ^® Vision, Siemens, Erlangen, Germany) with T1, T2 and T1 post-gadolinium (Magnevist, Berlex Laboratories, Wayne, NJ) weighting depicted a large 4 cm x 3.5 cm x 3.5 cm enhancing right temporoparietal mass with surrounding edema. The patient had a subtotal resection due to the proximity of the lesion to the Sylvian fissure and to the motor cortex. What is the most likely diagnosis?

DIAGNOSIS:

Glioblastoma multiforme (GBM) with infiltration along the optic tract. Radiographic features included an inhomogeneous mass with nodular, peripheral enhancement, and an infiltrative pattern of growth. Lesions which could potentially be included in the differential diagnosis are primary optic chiasmal glioma, meningioma, abscess, and metastases.

IMAGING FINDINGS:

Postoperatively, an incomplete left homonymous hemianopsia was evident. During radiotherapy, the patient developed new onset left-sided weakness. MR imaging demonstrated progressive disease, and she underwent a second debulking procedure. Radiotherapy was completed; however, following two cycles of BCNU, the patient developed worsening left-sided paresis and a central cranial nerve VII palsy. The ophthalmologic examination revealed a dense left homonymous hemianopsia, a new relative left afferent pupillary defect, and normal visual acuity but no evidence of band atrophy OS (figure 1). MR imaging confirmed worsening disease with involvement of the right optic tract and chiasm by tumor (figures 2,3). Procarbazine was offered for salvage chemotherapy but the patient continued to decline neurologically, expiring eight months from the time of her diagnosis.

DISCUSSION:

Glioblastoma multiforme and other infiltrative astrocytomas account for the majority of adult primary CNS malignancies. ¹ Direct involvement of the afferent pathways, such as the optic nerve, chiasm, optic tract, lateral geniculate body, radiations, and occipital cortex may result in focal visual loss. ² Visual loss may progress slowly or be sudden in onset.

Cases of primary GBMs involving the optic pathways have been described, although they are much less common than the childhood benign variant of optic gliomas. ³ The chiasm is most frequently involved; GBMs of the optic nerve and posterior pathways are rare. ³ In view of their aggressive growth, rapid progression to blindness and death is common. ³

Visual symptoms are found at presentation in approximately 30% of cases of primary brain tumors. ⁴ Visual impairment from central nervous system tumors generally can be attributed to either local effects (mass effect, edema, or direct infiltration) or to increased intracranial pressure. Increased intracranial pressure itself may be due to a rapidly expanding tumor, peritumoral edema, or to obstruction of cerebrospinal fluid outflow. ⁵ On rare occasions, distal vascular effects can occur, either due to local involvement of the vascular supply or related to herniation syndrome secondary to increased intracranial pressure.

Classically, malignant astrocytomas spread along white matter tracts. Spread of GBM along the corpus callosum results in a "butterfly" pattern, leading to bihemispheric involvement. Other common patterns of white matter spread include temporal lobe with ipsilateral basal ganglia, occipital lobe with splenium of corpus callosum, and basal ganglia with extension by way of the crus cerebri to the mesencephalon or contralateral thalamus. ²

This case presents an unusual pattern of spread along the optic tract post-chiasmatically, with evidence of continued spread to the level of the chiasm (figures 2,3). While it is interesting to note that the patient initially presented with no visual deficits, she later developed a progressive homonymous hemianopsia. The initial visual findings were consistent with reports of visual field cuts described for temporal lobe lesions, with homonymous hemianopsia or quadrantanopsia occurring in 67% cases. ⁵ Ultimately, the patient showed evidence of a right optic tract syndrome, including complete left homonymous hemianopsia and a contralateral afferent pupillary defect without any loss of visual acuity or color vision. ^2,6 The lack of optic atrophy (figure 1) is indicative of the rapid growth of this GBM.

Magnetic resonance imaging has been demonstrated to be the imaging modality of choice for diagnosis and demonstration of the progression of intracranial neoplasms, including malignant gliomas involving the visual pathways. ⁷ In particular, MR is superior in visualizing the intracanalicular portions of the optic nerve, chiasm, hypothalamus, and optic tract pathways due to elimination of bone artifacts and improved contrast enhancement resulting from subtle differences in fat content and hydration of neural tissue. ⁸