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Show / oumal of Cllllical Neuro- ol, hthalmology 12( 2): 77- 81, 1992. Craniopharyngioma: Pitfalls in Diagnosis Michael L. Brummitt, M. D., Lanning B. Kline, M. D., and Edward R. Wilson, M. D. ' 9 1992 Raven Press, Ltd., New York A 28- year old man presented with decreased vision and a bitemporal hemianopia. Magnetic resonance ( MR) imaging demonstrated what appeared to be an enlarged optic chiasm and, on T2- weighted images, hypersignal extending along the optic tracts. This was felt to represent an intrinsic chiasmal mass, most likely a chiasmal glioma. Biopsy specimens from the first craniotomy were nondiagnostic. With continued visual failure, the patient underwent a second operation, and the correct diagnosis of craniopharyngioma was established. This article emphasizes the difficulties encountered with neuroradiologic evaluation and histopathologic study of craniopharyngioma. Key Words: Craniopharyngioma- Chiasmal gliomaOptic nerve glioma. From the Combined Program in Ophthalmology and Department of Pathology, University of Alabama School of Medicine, Birmingham, Alabama, U. S. A. This work was presented in part at the 23rd Frank B. Walsh Society Meeting, February 22- 23, 1991, Salt Lake City, Utah. Address correspondence and reprint requests to Dr. Lanning B. Kline, Children's Hospital Tower, 1600 7th Avenue South, Suite 555, Birmingham, AL 35233, U. S. A. 77 The preoperative differentiation of an intrinsic from an extrinsic chiasmal tumor is of major importance in planning surgery. In the adult population an intrinsic lesion may be a malignant glioma, whereas an extrinsic tumor is likely to be a benign process, such as a pituitary adenoma. Magnetic resonance ( MR) is the imaging procedure of choice in evaluation of the optic chiasm ( 1). The ability of MR to resolve soft tissue detail has assisted greatly in distinguishing intrinsic from extrinsic intracranial tumors. We report a patient with progressive visual loss in whom both MR scanning and initial biopsy specimens suggested an intrinsic chiasmal tumor. However, with further evaluation it proved to be an extrinsic mass, a craniopharyngioma. CASE REPORT A 28- year- old man presented with a 2- week history of blurred vision. Initial evaluation by an optometrist revealed visual acuity of 20/ 25 au, normal pupillary responses, and normal external and funduscopic examinations. Automated perimetry was consistent with bitemporal hemianopia. A neurosurgeon detected no other physical or neurologic abnormalities. A cranial MR scan revealed a 2 cm x 3 cm suprasellar mass arising from the area of the optic chiasm, with hypersignal extending along the optic tracts ( Fig. 1). The MR findings were felt to be most consistent with an intrinsic chiasmal tumor, probably a glioma. At craniotomy, the chiasm was noted to be " markedly enlarged," and " grayish abnormal tissue" was found within its lateral aspect. Multiple biopsies were taken from the junction of the right optic tract and chiasm, and approximately 2 ccs of bloody fluid was aspirated from this area. The clinical impression at the time of the surgery was " optic nerve glioma." 78 M. L. BRUMMITT ET AL. FIG. 1. Preoperative cranial MR imaging. Left, coronal T1- weighted scan with gadolinium enhancement demonstrates hyperintense suprasellar mass. Right. axial T2weighted scan shows hypersignal along both optic tracts ( arrows). After review of the biopsies by several pathologists, the condition was interpreted as " acute and chronic inflammation with reactive gliosis" ( Fig. 2). Diagnostic possibilities included infectious process, multiple sclerosis, chiasmal glioma, and sec-ondary reactive changes near a neoplasm. Postoperatively the patient was placed on systemic steroids ( prednisone, 80 mg/ day). As the steroids were tapered the patient reported further loss of vision. FIG. 2. Initial biopsy specimen. Reactive astrocytosis and lymphocytic infiltrate from region of optic chiasm. H & E x 392. CRANIOPHARYNGIOMA: PITFALLS IN DIAGNOSIS 79 Neuro- ophthalmologic examination revealed visual acuity of 20/ 200 aD and 20/ 20 as. Color vision was diminished on the right. Pupillary testing and the fundi were normal. Visual fields demonstrated an incongruous left homonymous hemianopia, which may, in part, have been due to the previous surgical procedure. MR scanning showed persistence of both the suprasellar mass and hyperintense signal along the optic tracts. The patient underwent a second craniotomy. The chiasm again was found to be markedly swollen. After careful dissection, it became apparent a mass was draped around the chiasm. It was opened and was found to contain viscous fluid with refractile crystals. Frozen sections from the lesion confirmed the diagnosis of craniopharyngioma ( Fig. 3). Total removal of the tumor was achieved. Over the next 6 months the patient experienced recovery of vision to 20/ 30 00 and 20/ 20 as. Visual field testing revealed an incongruous left homonymous hemianopia. The right optic disc demonstrated mild diffuse pallor, whereas the left was normal. Repeat MR showed resolution of the suprasellar mass and changes along the optic tracts ( Fig. 4). DISCUSSION Craniopharyngiomas are thought to be derived from the remnants of Rathke's pouch. They may be cystic, often with high cholesterol content, or solid. The histologic diagnosis is established by identification of stratified squamous epithelium with basal columnar epithelium supported by a collagenous basement membrane. There may be trabeculae of epithelial cells supported by a loose fibrous stroma, reminiscent of the enamel organ of the tooth. Craniopharyngiomas contain calcifications in 75% of cases. At times there may be foci of lymphocytic infiltration within the fibrous stroma of the tumor and in neural parenchyma adjacent to the mass ( 2). As noted by Burger and Vogel ( 3), dense astrocytic gliosis adjacent to a craniopharyngioma may be misinterpreted as a glioma. The initial biopsy in our case was restricted to a small area of optic chiasm because the lesion was pre- and intraoperatively thought to be an intrinsic chiasmal lesion. After the initial pathologic diagnosis of nonspecific reactive changes, this case was sent for expert pathologic consultation. One expert returned a diagnosis of " consistent with viral infection," whereas another indicated that the lesion was a pilocytic astrocytoma. Both of these interpretations underscore the importance of not overinterpreting nonspecific microscopic alterations. Since dense reactive astrocytosis and lymphocytic infiltration can be seen in brain adjacent to craniopharyngioma, the pathologist should exhibit caution in the interpretation of a small sample from the base of the brain. The cystic and solid appearances of craniophar- FIG. 3. Second surgical specimen. Characteristic epithelium of craniopharyngioma overlying stroma with lymphocytic infiltrate. H & E x 392. JClin Neuro- ophthalmol, Vol. 12. No. 2, 1992 80 M. L. BRUMMITT ET AL. FIG. 4. Postoperative cranial MR imaging. Left. coronal Tl- weighted scan with gadolinium enhancement reveals decreased size of suprasellar mass and vIsible portions of the optic chiasm ( arrows). Right, axial T2- weighted scan demonstrates resolution of hypersignal along the optic tracts. yngioma are reflected in its variable MR characteristics ( 4). Most frequently, high intensity on Tlweighted scans is seen with cystic lesions containing high cholesterol content or methemoglobin. However, this tumor also may be of moderate or low Tl signal intensity, and appearance on T2weighted images is also variable. Computed tomography ( CT) has been shown to be superior to MR in the detection of tumoral calcification. Both the rare intrachiasmatic form of craniopharyngioma and an extrinsic mass may appear radiologically as an intrinsic tumor of the chiasm. This was reported before the advent of modern neuroimaging techniques ( 5), but may also occur with CT ( 6) and MR ( 7). Of particular interest is the recent report of Youl and co- workers ( 8). MR scanning in three patients with craniopharyngioma revealed apparent intrinsic tumor of the chiasm with hypersignal along the optic tracts. In two, the lesions were found to be extrinsic to the chiasm, whereas in the third, the tumor lay partly within the chiasm. The extension of swelling and high signal intensity on T2weighted MR images along the optic tracts had not been previously reported with craniopharyngioma. However, similar changes have been observed in cases of chiasma I glioma ( 1,9) and metastatic medulloblastoma ( 10). Youl et al. ( 8) speculate that this hyperintense signal seen with MR is caused by ] Clin Neu, o- aphthalmoL Vol. 12. No. 2. 1992 disruption of the blood- brain barrier and the source of the edema fluid is the lesion itself. Both the pathology and neuroradiology of craniopharyngioma led to diagnostic confusion in our patient. The initial biopsy proved inadequate primarily because of the close association of tumor and chiasm. Only tissue demonstrating reactive changes next to the neoplasm was obtained at the first craniotomy. The neuroradiologic findings influenced the expectation of the neurosurgeon during the first operation. The expanded chiasm seen at surgery was consistent with the MR findings, and a probable intrinsic tumor led to conservative surgical management. This case also emphasizes that MR scanning may on occasion fail to distinguish an intrinsic from extrinsic tumor of the chiasm. REFERENCES 1. Albert A, Lee BCP, Sait- Louis L, Deck MDF. MRI of optic chiasm and optic pathways. AJNR 1986; 7: 255-- 8. 2. Russell OS, Rubinstein LJ. Pathology of tumors of the nervous system, 5th ed. Baltimore: Williams & Wilkins, 1989: 697~. 3. Burger PC, Vogel SF. Frozen section interpretation in surgical neuropathology. I. Intracranial lesions. Am J Surg PathoI1977; 1: 323- 47. 4. Posey E, Kortman KE, Flannigan BO, Tsuruda J, Bradley WG. MR of craniopharyngioma. Am J Radial 1987; 149: 383-- 8. CRANIOPHARYNGIOMA: PITFALLS IN DIAGNOSIS 81 5. Block MA, Goree JA, Jiminez } p. Craniopharyngioma with optic canal enlargement simulating glioma of the optic chiasm. JNeurosurg 1973; 39: 523-- 7. 6. Duff TA, Levine R. lntrachiasmatic craniopharyngioma. J Neurosurg 1983; 59: 176- 8. 7. Brodsky MC, Hoyt WF, Barnwell SL, Wilson CB. lntrachiasmatic craniopharyngioma: a rare cause of chiasmal thickening. JNeurosurg 1988; 68: 300- 2. 8. YouI BD, Plant GT, Stevens JM, Kendall BE, Symon L, Crockard HA. Three cases of craniopharyngioma showing optic tract hypersignal on MR!. Neurology 1990; 40: 1416- 9. 9. Bognanno JR, Edwards MK, Lee TA, Dunn OW, Roos KL, Klatte EC. Cranial MR imaging in neurofibromatosis. AJNR 1988; 9: 461- 8. 10. Barkovich AJ. Paediatric neuroimaging. New York: Raven Press, 1990: 157. JClin Neuro- ophthalmol, Vol. 12, No. 2, 1992 |
