Neurology India Medknow Publications on behalf of the Neurological Society of India ISSN: 0028-3886 EISSN: 1998-4022 Vol. 58, Num. 6, 2010, pp. 833-840

Neurology India, Vol. 58, No. 6, November-December, 2010, pp. 833-840

Original Article

Optic chiasmatic-hypothalamic gliomas: Is tissue diagnosis essential?

Kalyan Bommakanti¹, Manas Panigrahi², Rani Yarlagadda³, C Sundaram⁴, Megha S Uppin⁴, AK Purohit¹

¹ Department of Neurosurgery, Nizam's Institute of Medical Sciences, Hyderabad, India
² Department of Neurosurgery, Krishna Institute of Medical Sciences, Secunderabad, India
³ Department of Radiology & Imageology, Nizam's Institute of Medical Sciences, Hyderabad, India
⁴ Department of Pathology, Nizam's Institute of Medical Sciences, Hyderabad, India
Correspondence Address: Manas Panigrahi, Department of Neurosurgery, Krishna Institute of Medical Sciences, Secunderabad, India, manaspanigrahi@live.com

Date of Acceptance: 13-Jul-2010

Code Number: ni10243

PMID: 21150045
DOI: 10.4103/0028-3886.73738

Abstract

Background: Optic chiasmatic-hypothalamic gliomas are sellar-suprasellar lesions with variable radiological features. The advocated treatment is mainly primary radiotherapy without a histological diagnosis. However, in developing countries, like India infective granulomas (tuberculomas) in the suprasellar region radiologically can mimic optic chiasmatic-hypothalamic gliomas. Hence primary radiotherapy without histological confirmation may have deleterious consequences.

Aim: The aim of the paper was to analyze the sensitivity and specificity of magnetic resonance imaging (MRI) in these lesions and to analyze the feasibility of primary radiotherapy.

Patients and Methods: The magnetic resonance imaging (MRI) characteristics of 24 patients with either histologically proven optic chiasmatic "pilocytic astrocytoma" or radiologically suspected optic chiasmatic-hypothalamic gliomas were analyzed. They were grouped into three groups on the basis of radiological features and treated with a suspected diagnosis. The final diagnosis was correlated with preoperative diagnosis, and the feasibility of managing these lesions without a histopathological confirmation is discussed.

Results: The three radiological groups were: Group-1 solid tumors with or without microcysts in 9 patients (histology: 8 pilocystic astrocytomas and 1 tuberculoma); Group-2 mixed tumors with solid and cystic components in 9 patients (histology: 7 pilocytic astrocytomas and 2 craniopharyngiomas); Group-3 ring enhancing lesions in 6 patients (all the 6 patients initially received antituberculous treatment, in 3 patients the lesion resolved and in the remaining 3 patients the lesion was subjected to biopsy as it did not resolve, the biopsy was suggestive of pilocytic astrocytoma). Thus, MRI was shown to have a sensitivity of 83.33% and a specificity of 50% for diagnosing optic chiasmatic-hypothalamic gliomas.

Conclusions: Various lesions like craniopharyngiomas, tuberculomas can mimic optic chiasmatic-hypothalamic gliomas radiologically, and it is not possible to diagnose them with certainty on the basis of radiological findings alone. Biopsy and tissue diagnosis should always be sought before instituting radiotherapy or chemotherapy for optic chiasmatic-hypothalamic gliomas.

Keywords: Hypothalamic glioma, optic chiasmatic-hypothalamic glioma, optic pathway gliomas, pilocytic astrocytoma, suprasellar tuberculoma

Introduction

Optic pathway gliomas account for approximately 5% of brain tumors ^[1] and 10% to 15% of supratentorial tumors in children. ^[2] Majority of the optic chiasmatic-hypothalamic gliomas (OCHGs) are pilocytic astrocytomas ^[1],[2] and correspond to World Health Organization (WHO) grade I. They have an indolent course. Only a few behave aggressively. ^[3] OCHGs present with visual disturbances, hormonal deficits secondary to hypo-pituitarism, headache, episodes of vomiting due to obstructive hydrocephalus, disturbed cognition and failure to thrive. These clinical features are reflective of their location, rather than their histology. Other sellar-suprasellar lesions like pituitary adenoma, suprasellar meningioma, germinoma, craniopharyngioma, rathke cleft cyst, dermoid, tuberculoma, sarcoidosis may present with similar clinical features, and so differentiating these lesions from OCHGs on the basis of clinical features alone is not always possible. The management of each of these lesions differs considerably from that of OCHGs. So a definitive diagnosis is essential for deciding the line of management. Radiological assessment using computed tomography (CT) and magnetic resonance imaging (MRI) can aid in reaching a probable diagnosis and in formulating an appropriate management strategy. But is it advisable to institute the definitive therapy on the basis of radiological features without histopathological confirmation? A number of studies have been published in the literature, where radiotherapy or chemotherapy was administered only on the basis of clinical and radiological features without a histopathological confirmation. ^{[4],[5],[6],[7],[8],[9],[10],[11],[12],[13],[14],[15],[16],[17]} We have done a "Pubmed" search and we couldn't find articles in English addressing this issue.

The imaging characteristics of OCHGs vary widely and can resemble the pathological entities mentioned above. In the present study, an attempt has been made to describe the radiological features of OCHGs. Other pathological entities which can resemble OCHGs are identified, and we have attempted to analyze the requirement of tissue diagnosis for definitive management of OCHGs.

Patients and Methods

Patients with either a preoperative radiological diagnosis of OCHG or a histopathological diagnosis of pilocytic astrocytoma (of suprasellar region) and operated at the Nizam's Institute of Medical Sciences, India, between January 2004 and December 2008 were included in the study. Their case notes and MR images were retrieved. All the patients underwent MRI with T1-weighted, T2-weighted, FLAIR (fast fluid-attenuated inversion-recovery) and contrast-enhanced T1-weighted spin echo sequences. They were evaluated for location, size, shape and margins of tumor; extent of involvement of optic pathway and hypothalamus; infiltration of surrounding structures; and intensity on T1-weighted, T2-weighted and FLAIR images. The number of cysts and their sizes were also recorded. In contrast-enhanced images, the pattern of enhancement of the solid and cystic components was analyzed. Patients with ring-enhancing lesions were evaluated with MR spectroscopy. The radiological diagnosis was correlated with histopathological diagnosis in operated cases.

Results

A total of 24 patients were included in the study. On the basis of MRI morphology, the lesions were divided into three distinct groups. Predominantly solid lesions were grouped under group 1; mixed lesions with solid and cystic components, under group 2; and ring-enhancing lesions, under group 3.

Group 1

Predominantly solid lesions with or without evidence of microcysts were included in group 1 and this type of lesion was seen in nine patients [Figure - 1] and [Table - 1]. The lesions were round to oval, hypointense or isointense on T1-weighted images; hyperintense on T2-weighted images; and showed enhancement on post-contrast images. Preoperatively, all these nine lesions were considered as OCHGs. However, histopathological examination was OCHGs (pilocytic astrocytomas) in eight and tuberculoma in one. Optic chiasma and hypothalamus were involved in all the eight patients, OCHG extended anteriorly to involve left optic nerve in one patient and extended posteriorly to involve the optic tracts in two patients. In two patients the OCHGs were large enough to indent the medial temporal lobes and infiltrate bilateral capsuloganglionic regions. In all the patients the margins of the tumor were well demarcated. Ventriculomegaly was evident in three patients. On T1-weighted images, the lesions were isointense to the gray matter in two patients and hypointense in six patiens. One patient had specks of hyperintensity. On T2-weighted and FLAIR images, the lesions were hyperintense in seven patients, and one of the OCHG was heterogeneous. In contrast-enhanced images, all the lesions enhanced. The enhancement was intense and heterogeneous in six patients, homogeneous in one patient, minimal and patchy in one patient. The lesion, which was a tuberculoma on histopathological examination, was oval, isointense on T1-weighted images, hyperintense on T2-weighted images, showed heterogeneous enhancement and involved the optic chiasma and hypothalamus, causing ventriculomegaly. Postoperatively this patient was started on anti-tubercular drugs. The lesion showed resolution in the follow-up scans.

Group 2

Lesions with both solid and cystic components were included in group 2 and this type of lesion was seen in nine patients [Figure - 2] and [Table - 2]. Preoperatively, all of the lesions were considered as OCHGs. However, histological examination revealed OCHGs (pilocytic astrocytomas) in seven and craniopharyngiomas in two. In OCHGs, the solid component was hypointense or isointense on T1-weighted images; hyperintense on T2-weighted images and FLAIR images; and enhanced heterogeneously in contrast images. The cysts were hypointense on T1-weighted images; hyperintense on T2-weighted images; and hyperintense or isointense on FLAIR images. The walls of the cysts did not enhance in three patients and enhanced in four patients. Ventriculomegaly was evident in six patients. In the two patients with craniopharyngiomas, solid component was hypointense on T1-weighted images and hyperintense on T2-weighted images. A single large cyst was seen in these two patients, and the cysts were hypointense on T1-weighted images and hyperintense on T2-weighted images. The solid component showed mottled enhancement. The cyst walls also enhanced. No calcification was evident in CT scans. Thus in these two craniopharyngiomas, CT scan was also not useful in differentiating them from OCHGs.

Group 3

This pattern included solid suprasellar ring-enhancing lesions and this type of pattern was seen in six patients [Figure - 3] and [Table - 3]. The lesions were hypointense on T1-weighted images and hyperintense on T2-weighted and FLAIR images. Optic chiasma and hypothalamus were involved in all the six lesions. The lesions demonstrated irregular ring enhancement in contrast images. In one patient, enhancement extended up to the tectum, and the conglomerate ring enhancement resembled a "garland." Ventriculomegaly was seen in five patients. Based on these radiological features, these lesions were all initially managed as tubercular granulomas, as tuberculosis is endemic in India. Corroborative clinical evidence for tuberculosis was sought. Erythrocyte sedimentation rates, total leukocyte counts, chest X-rays were normal in all. Cerebrospinal fluid analysis was performed in two patients, and it was not suggestive of tuberculosis. Two patients underwent MR spectroscopy, which yielded nonspecific results. All of them were started on anti-tuberculosis regimen. Repeat MR imaging after three months showed resolution of the lesion in three patients. The remaining three lesions did not respond to an adequate trial of anti-tubercular drugs. These three patients were subjected to craniotomy and biopsy. On histopathological examination, the lesions in these three patients were OCHGs (pilocytic astrocytomas).

Discussion

Optic pathway gliomas represent 3% to 5% of childhood brain tumors. ^[17],[18] Majority of the OCHGs are pilocytic astrocytomas. They are commonly seen in children and young adults. Approximately 75% of these tumors are diagnosed during the first decade of life, and 60% are diagnosed before the age of 5 years. ^[19],[20] In this series, all the patients were under 35 years of age, with 13 (72.22%) patients aged less than 20 years. The association between OCHGs and neurofibromatosis is well known. In patients with neurofibromatosis, OCHGs most commonly involve the intra-orbital optic nerve (66%), followed by the chiasma (62%). In patients without neurofibromatosis, OCHGs most commonly involve the chiasma (91%), and the optic nerves are involved in 32% of OCHGs. ^[3] None of the patients in our series had stigmata of neurofibromatosis, and hence we couldn't study the radiological features of OCHGs in patients with neurofibromatosis. In our series, in OCHGs, optic chiasma was involved in 100%, hypothalamus in 88.88%, optic chiasma alone in 11.11%, optic tracts in 27.7% and optic nerve in 11.11% of the patients.

OCHGs have variable radiological features. They appear sharply demarcated and smoothly marginated. In plain CT images, majority of OCHGs are hypodense or isodense, and a few are hyperdense. Most often they show moderate-to-marked enhancement. Rarely fleck-like tumor calcifications can be seen. They are isointense to slightly hypointense relative to brain on T1-weighted images and hyperintense on T2-weighted images. Cystic elements, either microcysts or macrocysts, are common. ^[21] The presence of cystic components is significantly more common in patients without neurofibromatosis. ^[3]

In our study Group 1 lesions were predominantly solid tumors with or without evidence of microcysts. Majority of the lesions were hypointense on T1-weighted images; hyperintense on T2-weighted images and FLAIR images; and showed enhancement on contrast administration, as seen in [Figure - 1]. Although pilocytic astrocytomas are benign, they enhance intensely with contrast. This is because of abundant vascularity of the tumor. ^[21],[22] The enhancement can be homogeneous or heterogeneous. Among the nine lesions included in this group, eight were OCHGs (pilocytic astrocytomas) and one was a tuberculoma. Hence tuberculoma should be considered in the differential diagnosis along with other solid sellar-suprasellar enhancing lesions, like pituitary macroadenoma, suprasellar meningioma and germinoma. Tekkok et al.[23] have reported a case of OCHG presenting as a huge intrasellar mass resembling a pituitary adenoma radiologically. Wilson et al.[24] have described a case of suprasellar germinoma mimicking OCHG and have emphasized the requirement of histological confirmation.

In our study Group 2 lesions were mixed tumors with solid and cystic components, as shown in [Figure - 2]. The solid component was isointense to hypointense on T1-weighted images; and heterogeneously hyperintense on T2-weighted images and FLAIR images. The solid component enhanced following contrast administration. The cysts were hypointense on T1-weighted images and hyperintense on T2-weighted images. The walls of cysts showed enhancement in 28% of patients. Cysts represent regressive changes owing to the indolent nature and slow clinical evolution of pilocytic astrocytomas. ^[25] Size of the cysts is variable. In our series, almost all of the cysts, except one, formed <30% of the total tumor volume. But the cysts may be massive, the tumor being a mural nodule ^[26] ; or multiple and small, as seen in some of group-1 OCHGs. The cystic component is apparently rich in factors capable of stimulating vascular proliferation. Glomeruloid vasculature is seen within the tumor, in the cyst walls, and occasionally at a distance from the tumor. ^[21],[22] This explains the narrow band of contrast enhancement seen at the circumference of some cysts. Craniopharyngiomas, rathke cleft cysts, dermoids should be considered in the differential diagnosis of group-2 OCHGs. In Matson's ^[27] large series of tumors in children, craniopharyngiomas were the most common non-glial tumors and constituted 9% of his series. Craniopharyngiomas have a solid component which is isointense or hypointense on T1-weighted images and heterogeneously hyperintense on T2-weighted images. Tumor calcification on plain radiographs is visualized in 85% of pediatric cases. ^[28] It enhances intensely, and the enhancement appears mottled as an indirect result of decreased signal intensity due to tumor calcification. A single large cyst or multiple cysts are seen. The intensity of cysts is ^[29] highly variable and depends on the contents of the cysts. ^[30] They can be hyper on T1-weighted images, hypo on T2-weighted images; hypo on T1-weighted images, hyper on T2-weighted images; hyper on both T1-weighted and T2-weighted images. The walls of the cysts also enhance intensely with contrast. ^[30] In some cases, the craniopharyngioma cysts may be homogeneously enhancing with contrast because of diffusion of contrast into the cyst fluid, giving the appearance of a solid mass. ^[28] Cysts of variable intensity, cysts hyperintense on T1-weighted images and mottled enhancement of the solid portion, favor the diagnosis of craniopharyngioma. But craniopharyngiomas may present with a single cyst which is hypointense on T1-weighted images, hyperintense on T2-weighted images without evidence of calcification and can resemble OCHGs. This was seen in 2 of our patients. Furthermore, craniopharyngiomas may show edema along the optic tracts, that is, the "moustache" sign, ^[31] and this may be confused with optic tract involvement of OCHGs. Bisson et al.[28] have reported 2 cases of OCHGs appearing like craniopharyngiomas on neuroimaging. Thus it is not possible to definitely distinguish craniopharyngiomas from OCHGs with neuroimaging. Rathke cleft cysts have no solid component and do not enhance. Dermoid cysts are common in sellar and parasellar regions. ^[30] On T1-weighted images, high signal intensity is because of fat. Occasionally fat-fluid level is seen. Dermoid cysts have a lining of keratinized squamous epithelium; and adnexia-like hair, sebaceous glands and sweat glands. This complexity results in heterogeneous intensity on T2-weighted images. Rupture of dermoid cysts leads to spillage of its contents into the subarachnoid space, and they are seen as hyperintense droplets on T1-weighted and T2-weighted images.

Group-3 lesions in our series were solid suprasellar ring-enhancing lesions. They were hypointense on T1-weighted images, hyperintense on T2-weighted and FLAIR images and showed irregular ring enhancement in contrast films [Table - 3]. Granulomas, like tuberculomas, show ring enhancement and are to be considered in the differential diagnosis. Although ring enhancement of granulomas is well known, ring enhancement of OCHGs is not reported in the literature. Jain et al.[32] could find, in literature, 3 cases of suprasellar tuberculomas in children, and Ashkan et al.[33] could find 13 cases of sellar and suprasellar tuberculomas in adults. Thus, even though rare, in the wake of increasing spread of tuberculosis worldwide, tuberculomas should be considered in the differential diagnosis. This becomes even more important in countries like India, where tuberculosis is endemic. These patients should be biopsied if they are unresponsive to an adequate course of anti-tubercular drugs. Associated thickening of pituitary stalk, if present, increases the likelihood of sellar tuberculomas. ^[34,35] Other granulomas like sarcoidosis generally present with focal granulomas ^[36] with very few small necrotic areas, ^[37] and they enhance uniformly. Ring enhancement is not seen. In addition, isolated intracranial sarcoid granulomas without lesions in the chest are unusual.

Is tissue diagnosis essential?

The diagnosis of the optic chiasmatic-hypothalamic gliomas on the basis of radiological features is often difficult. This is illustrated in our case series and reports from literature, as discussed above. In 3 (16.66%) out of the 18 patients with biopsy-proven OCHGs, the radiological features were not typical of glioma, and glioma was not suspected preoperatively. On the other hand, 3 (16.66%) out of 18 patients with radiological features suggestive of OCHG had a different pathological lesion on histopathological examination. This shows that MRI has a sensitivity of 83.33% and specificity of 50% for diagnosing OCHGs, as shown in [Table - 4]. In the literature, there are many reports of radiotherapy or chemotherapy having been instituted for OCHGs on the basis of radiological features. ^{[4],[5],[6],[7],[8],[9],[10],[11],[12],[13],[14],[15],[16],[17]} As it is not possible to diagnose OCHGs on the basis of radiological features with certainty, it is not advisable to start radiotherapy or chemotherapy on radiological grounds alone.

Acknowledgments

Many thanks to Dr. A. Praveen, Dr. B. P. Sahu, Dr. M. V. Saradhi, Dr. Suchanda and other members of the Department of Neurosurgery, NIMS, for their valuable support in the management of these patients. Special thanks to Dr. Sree Bhushan Raju for his painstaking efforts in revising this paper.

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