imaging of craniopharyngioma

Childs Nerv Syst (2005) 21: 635 639 DOI 10.1007/s00381-005-1245-y SPECIAL ANNUAL ISSUE John G. Curran Erin O Connor Imaging of craniopharyngioma Received: 30 May 2005 Published online: 3 August 2005 # Springer-Verlag 2005 J. G. Curran (*). E. O Connor Department of Medical Imaging, Children s Memorial Hospital, 2300 Children s Plaza, Chicago, IL, 60614, USA e-mail: jcurran@childrensmemorial.org Tel.: +1-773-8803541 Fax: +1-773-8803517 Abstract Background: Craniopharyngiomas are present with a wide range of appearances, but the existence of cysts, calcification, and enhancement in a suprasellar tumor strongly favors the diagnosis. Discussion: There is a significant differential diagnosis that must be considered. The pre- and postoperative imaging of craniopharyngioma is reviewed. Keywords Cerebral angiography. Child. Craniopharyngioma/ diagnosis. Craniopharyngioma/ surgery. Image processing, computerassisted. Magnetic resonance imaging. Pituitary neoplasms/ diagnosis. Tomography, X-ray computed General imaging features of craniopharyngioma The characteristic imaging finding of craniopharyngioma in a child is an enhancing suprasellar mass that is calcified and cystic on CT. When two out of these three features are present, craniopharyngioma is still the most likely diagnosis [1]. The tumor usually demonstrates T1 high intensity on MR, reflecting the protein or cholesterol content of the motor oil-like fluid found in the tumor cysts [2]. Rarely on plain skull film, craniopharyngioma may be suspected by the presence of sellar or suprasellar calcifications. Usually from the initial imaging, a craniopharyngioma can be located in the sella, and/or if partially or entirely suprasellar, can be described as pre- or retrochiasmatic. Determination of size is important at presentation, as tumors greater than 5 cm in diameter have a recurrence rate of more than 80%, whereas in tumors less than 5 cm, the recurrence rate is 20% [2]. Rate of growth is slow, so a rapid interval change in size in the absence of tissue diagnosis may require a reassessment of the etiology of the tumor. By CT examination, approximately 90% of childhood craniopharyngiomas calcify. The percentage drops to approximately 70% in adults. The typical appearance of an adamantinomatous type craniopharyngioma is a mixed cystic and solid mass on CT, usually with a solid focus in the sella, and cystic components arising above it. The papillary type of tumor is more often solid with less common incidence of calcification [2]. By MRI examination, the tumor is of variable T1 signal, often hyperintense. The T1 hyperintensity is usually secondary to high protein content in the cyst fluid. However, other causes of T1 hyperintensity in craniopharyngiomas have been described fat, cholesterol, hemorrhage, or even mild calcification [4]. The mixed solid and cystic nature of the tumor is clearer on MR than on CT. Occasionally with small cysts, even on postcontrast study, the heterogeneous nature of the tumor may not be apparent on CT. This problem does not occur with MR [3]. Even small cysts are identifiable and the smaller solid portion of the tumor is usually heterogeneous or even isointense with brain (Fig. 1). On MR T2-weighted sequences, including Fluid Attenuated Inversion Recovery (FLAIR), the solid portion is again usually heterogeneous, whereas the cysts are invariably hyperintense (Fig. 2). The calcifications, in the solid portion of the tumor or in the peripheral rim, are

636 Fig. 1 Eleven-year-old boy with several week history of vomiting, weight loss, ataxia, and abnormal behavior. a Axial CT noncontrast image demonstrating a sellar mass with an irregular calcified component. b Sagittal noncontrast T1 image demonstrating a large sellar and suprasellar mass with cysts of varying intensity, mainly hyperintense. c Coronal noncontrast T1 image demonstrating multiple cysts of varying intensity. Hydrocephalus is also apparent. d Axial T2 image showing cysts mainly hyperintense, but of varying intensity. e Axial FLAIR image showing cysts more uniformly hyperintense. f Sagittal postcontrast T1 image showing peripheral rim enhancement of the cysts, and heterogeneous enhancement of the solid lower portion of the tumor. g Coronal postcontrast T1 image showing mainly the peripheral rim enhancement of the cysts hypointense on T2. They stand out particularly on a susceptibility sequence such as Gradient Recalled Echo (GRE) [3]. Following contrast, there is almost invariable enhancement of the solid portion and the peripheral rim of the cystic portion on both CT and MR (Fig. 3). Contrast is essential for the diagnosis on CT. In one study, three of nine tumors were not identified on the noncontrast CT [3]. The enhancement of the solid portion may be either uniform or patchy and heterogeneous. Enhancement patterns in a given tumor are similar on both CT and MR [3]. One CT and MR study of 26 patients sought to divide the appearance of craniopharyngioma into patterns, i.e., solid, calcified, proteic-like, CSF-like, hematic-like, and fatty [5] (Table 1). There were no correlations between patterns except that in no case did the CSF-like and the proteic-like pattern coexist. Calcified and proteic-like tumors tended to be large. Hematic-like and CSF-like tumors tended to be small [5]. The most useful radiological findings to describe craniopharyngiomas are lesion size, cyst characteristics, and vessel encasement [5]. On angiography, the tumor is usually avascular with displacement of the major vessels of the circle of Willis. Recommended imaging technique MR is the imaging modality of choice [3]. An MR examination should include thin T1 sagittal and coronal sections both pre- and postcontrast through the sella and suprasellar region. It is useful to include a precontrast fat saturation T1 sequence as it will help to identify the posterior pituitary bright spot. Additional sequences may be helpful in answering specific questions: FLAIR is useful in delineating cystic portions of tumor (which will be hyperintense) vs loculated portions of the third ventricle or other CSF spaces (which will tend to be isointense). GRE is useful as a susceptibility sequence in demonstrating calcification more clearly, or possibly demonstrating blood products if there is a question of hemorrhage. Diffusion Weighted Imaging (DWI) (diffusion imaging) is useful in the differential diagnosis if an epidermoid is suspected. MR spectroscopy demonstrating a significant lipid content may be useful.

637 Imaging in the differential diagnosis of craniopharyngioma The most commonly listed differential diagnoses are: 1. Pituitary adenoma 2. Hypothalamic or optic pathway glioma 3. Rathke s pouch cyst 4. Epidermoid tumor Other considerations would include: 5. Thrombosed aneurysm 6. Simple arachnoid cyst 7. Masses of infectious or inflammatory origin 8. Pituicytoma 9. Colloid cyst of the third ventricle Pituitary adenoma is uncommon in children, whereas the peak age group for craniopharyngioma is 5 15 years, but nonetheless, this tumor is occasionally seen. It is often noncalcified, so a noncontrast CT is a helpful component of the diagnostic workup. Pituitary adenoma often is greater Fig. 2 Nine-year-old girl with acute visual loss in the left eye. Provisional diagnosis of optic neuritis. a Axial noncontrast CT image showing a sellar mass with faint peripheral calcification. b Axial noncontrast CT image showing partially solid, partially cystic tumor. c Sagittal noncontrast T1 image showing mainly hypointense, partly solid, partly cystic tumor with both sellar and suprasellar components. d Coronal T2 image showing a heterogeneous hyperintense sellar and suprasellar mass. e Sagittal postcontrast T1 image demonstrating fairly uniform enhancement of the majority solid portion of the tumor in bulk within the sella and has a tendency to expand the sella. Craniopharyngioma will on the other hand tend to show greater superior expansion, often with a small sellar component without expansion of the bony sella. A pituitary tumor with a cystic component and/or a degree of hemorrhage can be difficult to distinguish from a craniopharyngioma. Factors supporting the diagnosis of pituitary adenoma in a giant intra- and suprasellar mass include infrasellar extension, absence of calcification, and presence of low-signal cysts on T1-weighted images [6]. Hypothalamic or optic pathway gliomas lack two common features of craniopharyngiomas. They rarely have a sellar component (although when large may erode the sphenoid bone) and are rarely calcified. The tumors are usually isointense on T1 and usually lack a cystic component. If a cystic component or necrosis is present, it is usually dominated by the solid component of the tumor, whereas the cystic component is usually dominant in craniopharyngioma.

638 Fig. 3 Two and a half-year-old boy with several month history of polyuria and polydipsia. Now with strange eye movements. a Sagittal noncontrast T1 image demonstrating cysts of mixed hyper- and hypointensity. b Axial noncontrast T1 image demonstrating mixed hyper- and hypointense cysts. c Coronal T2 image demonstrating cysts of varying intensity, mainly hyperintense. d Sagittal postcontrast T1 image demonstrating heterogeneous enhancement of the lower solid portion of the tumor, with peripheral rim enhancement in the cystic portion Table 1 Semiological patterns of craniopharyngioma on MRI and CT Solid pole 100% Cystic component 92.3% Calcification 65.3% Proteic like 53.8% CSF like 23% Hematic like 19.2% Fatty component 15.3% Rathke s cleft cysts may at times be difficult to differentiate from small craniopharyngiomas. However, larger Rathke s cleft cysts are easier to differentiate as they typically do not contain a solid component, do not enhance, and are not calcified [7]. Epidermoid tumors may rarely occur in the suprasellar region. The substance of an epidermoid tumor may be identified by restricted diffusion; hence, the use of diffusion weighted imaging is recommended if that possibility is under consideration. Peripheral rim enhancement is less common in epidermoids [8]. Thrombosed aneurysms are a consideration in an older age group. They typically have an eccentric pattern of concentric circles within the mass. Identification of a residual lumen assists in confirming the diagnosis. Simple suprasellar arachnoid cysts contain neither calcification nor solid portion. They are typically bounded posterior by the membrane of Lilliquist. Inflammatory masses may occur in the suprasellar region. Usually, these are infective in nature such as granulomatous infections, but occasionally, other inflammations such as sarcoid or histiocytosis may manifest as suprasellar disease. Typically, these lesions are infiltrative, layering along the pituitary stalk and the adjacent undersurface of the brain, but occasionally, frank granulomas may occur in the suprasellar region giving rise to diagnostic difficulty. Granulomas are not usually calcified, are somewhat heterogeneous in signal, and often show diffuse enhancement. Lymphocytic hypophysitis, an adult condition, is an inflammation of the anterior pituitary gland and usually presents with an infiltrative appearance including thickened pituitary stalk rather than a mass. Pituicytoma, or granular cell tumor, a rare adult tumor of the neurohypophysis and infundibulum, gives rise to a suprasellar mass without significant compression of adjacent structures. The mass is noncystic and noncalcified and is closely associated with the pituitary stalk. Colloid cyst of the third ventricle may cause confusion with a high third ventricular craniopharyngioma. The tumor is of high signal on all sequences. However, the presence of a heterogenous suprasellar solid component and the noncollapse of the posterior third ventricle, despite a lesion

639 in the anterior, make the diagnosis of craniopharyngioma much more likely [8]. Postsurgical evaluation of craniopharyngioma The main focus of postsurgical evaluation is the determination of the presence and extent of residual tumor. However, in addition, the potential complications of surgery must be borne in mind. These include hypothalamic injury with associated endocrine abnormalities, injury to the pituitary gland, and vascular injury including pseudoaneurysm formation of adjacent structures. MR is essential in the immediate aftermath of craniopharyngioma surgery. Exact timing is not established, but imaging within the first postoperative week is the usual standard. The normal appearance is of interval reduction in tumor size. It is also common to identify residual tumor (best delineated on the postcontrast T1 images), even when there has been no residual tumor identified at the end of surgery [9]. There is usually no change in signal intensity of the cystic or of the solid portion of the tumor between the preoperative and postoperative scans. A fluid collection, isointense to CSF, and usually resolved by the second postoperative scan, is typically seen on all immediate postoperative scans [9]. With intraaxial lesions, luxury perfusion and disruption of the blood brain barrier may give rise to new or more extensive contrast enhancement postoperatively. However, in the case of craniopharyngioma as an extraaxial lesion, no new areas of enhancement are to be expected postsurgery. The emergence of such findings would therefore be a matter of concern [9]. Finally, the postoperative scan should usually demonstrate a resolution of hydrocephalus if present preoperatively and better visualization of the normal structures, such as the chiasm or pituitary stalk, in the suprasellar region, if these are intact. The second postoperative scan may show reduction of residual tumor volume when compared to the first postoperative scan. Although this may be attributed to interval radiation therapy [10], such a volume reduction may be seen in patients who have received no interval therapy [9]. As residual tumor volume reduction over months has also been seen in pituitary adenoma, presumably related to edema resolution, it has been suggested that an accurate estimation of residual tumor volume in craniopharyngioma may be obtained only at 2 3 months postsurgery [9]. The period of tumor shrinkage after radiation therapy is often long and varied (mean 29 months) [10]. Increase in size of residual tumor between the first and second postoperative scan has been identified in certain patients as attributable to interval radiation therapy, with further follow-up scans demonstrating a regression of the tumor [9]. Conclusion The imaging modality of choice for craniopharyngioma is MR. However, CT is very useful in determining the presence of calcification. The tumors present a wide variety of appearances, but the presence of cysts, calcification, and enhancement in a suprasellar tumor strongly favors the diagnosis. There is a significant differential diagnosis that must be considered. Postoperative follow-up with MR is essential, but potential pitfalls such as the relatively frequent presence of residual tumor even in a gross total resection, interval short-term increase in treated tumor, and the potentially long period of tumor shrinkage must be borne in mind. References 1. Fitz CR, Wortzman G, Harwood-Nash DC, Holgate RC, Barry JF, Boldt DW (1978) Computer tomography in craniopharyngiomas. Radiology 127:687 691 2. Osborn AG (2004) Diagnostic imaging brain. Amirsys Inc., Salt Lake City 3. Hald JK, Eldevik OP, Skalpe IO (1995) Craniopharyngioma identification by CT and MR imaging at 1.5 T. Acta Radiol 36(2):142 147 4. Ahmadi J, Destian S, Apuzzo MLJ, Segall HD, Zee CS (1992) Cystic fluid in craniopharyngiomas. MR imaging and quantitative analysis. Radiology 182:783 785 5. Molla E, Marti-Bonmati L, Revert A, Arana E, Menor F, Dosda R, Poyatos C (2002) Craniopharyngiomas: identification of different semiological patterns with MRI. Eur Radiol 12:1829 1836 6. Majos C, Coli S, Aguilera C, Acebes JJ, Pons LC (1998) Imaging of giant pituitary adenomas. Neuroradiology 40:651 655 7. Igarashi T, Saeki N, Yamaura A (1999) Long term magnetic resonance imaging follow-up of asymptomatic sellar tumors their natural history and surgical indications. Neurol Med Chir (Tokyo) 39:592 599 8. Wang YXJ, Jiang H, He GX (2001) Atypical magnetic resonance imaging findings of craniopharyngioma. Australas Radiol 45:52 57 9. Hald JK, Eldevik OP, Quint DJ, Chandler WF, Kollevold T (1996) Pre- and postoperative MR imaging of craniopharyngiomas. Acta Radiol 37:806 812 10. Hamamoto Y, Niino K, Adachi M, Hosoya T (2002) MR and CT findings of craniopharyngioma during and after radiation therapy. Neuroradiology 44:118 122