Letter

J.-F. Bonneville
Department of Radiology and Endocrinology
University Hospital of Liège, University of Liège
Liège, Belgium

Iread with interest the article of Park et al¹ published in the October issue of theAmerican Journal of Neuroradiology. Differentiation with MR imaging of a cystic or hemorrhagic pituitary adenoma from a Rathke cleft cyst (RCC) remains a common issue. In daily practice, this situation may be particularly confusing in a young woman with mild hyperprolactinemia whose symptoms are frequently hidden by taking contraceptive pills. Moreover, parallelism between the prolactin level and tumoral volume is missing in hemorrhagic microprolactinomas. Then, diagnosis of hemorrhagic microprolactinoma versus T1 hyperintense intrasellar mucoid RCC is challenging.

Park et al reported that the main differentiating features of pituitary adenomas are off-midline location, tilting of the pituitary stalk, fluid-fluid level, T2 hypointense hemosiderin rim, and septations, while Rathke cleft cysts are more likely located on the midline and frequently present with a T2 hypointense characteristic nodule.

Nevertheless, pituitary adenomas may be on the midline, for instance corticotroph adenomas. The fluid-fluid level is inconstant, particularly with fresh hemorrhage and a peripheral hemosiderin rim because of the absence of blood-brain barrier in the pituitary gland; septations are inconstant. On the other hand, Rathke cleft cysts may be, rarely, in an off-midline location, and their T2 hypointense waxy nodules are detected in no more than 70% of cases.

Moreover, the diagnostic tree model proposed by Park et al seems difficult to apply to the strictly intrasellar infracentimetric lesions, which are more and more frequently seen with high- resolution 3T scanners, either discovered fortuitously or in the assessment of hyperprolactinemia.

Ancillary signs are then welcome to differentiate RCCs from cystic or hemorrhagic pituitary adenomas.

The axial T1-weighted sequence is optimal for making the diagnosis of such RCCs: Strict midline location, regular convex symmetric anterior surface, and close contact with the posterior lobe are characteristic features.²

Furthermore, while intrasellar pituitary adenomas, even tiny ones, give rise to mass effect, such as bulging of the sellar diaphragm and eroding of the bony contours of the sella, intrasellar RCCs of equal volume give rise to a less important mass effect or even to no mass effect, most probably because of intracystic low pressure, at least with an asymptomatic RCC (Fig 1).

This observation is helpful in the presence of the not-so-rare concomitant intrasellar pituitary adenoma and RCC, in which the soft RCC is deformed by the firmer pituitary adenoma, even if the latter is smaller (Fig 2).

References

1. Park M, Lee SK, Choi J, et al. Differentiation between cystic pituitary adenomas and Rathke cleft cysts: a diagnostic model using MRI. AJNR Am J Neuroradiol 2015;36:1866–73
2. Bonneville JF, Bonneville F, Cattin F. Magnetic resonance imaging of pituitary adenomas. Eur Radiol 2005;15:543–48

Reply

M. Park, S.S. Ahn
Department of Radiology, Research Institute of Radiological Science
Yonsei University, College of Medicine
Seoul, Korea

We appreciate the comments from Jean-François Bonneville on our study entitled “Differentiation between Cystic Pituitary Adenomas and Rathke Cleft Cysts: A Diagnostic Model Using MRI.”¹ As Dr Bonneville mentioned, differentiating cystic or hemorrhagic adenoma and Rathke cleft cyst (RCC) is sometimes challenging, and preoperative differentiation of these conditions is important for treatment planning^2,3; therefore, we suggested a diagnostic tree model for differentiating cystic pituitary adenoma from RCC by using preoperative MR imaging and reported an improved diagnostic accuracy when using the diagnostic tree model.¹

We agree with Dr Bonneville that pituitary adenomas, especially corticotroph-secreting adenomas, may be on the midline as seen in Fig 5, and 16.7% of pituitary adenomas in our study were also located on the midline.¹ In addition, other imaging findings were seen with various frequencies: fluid-fluid levels in 68.5%, T2-hypointense rims in 75.9%, septations in 38.9% of pituitary adenomas, and intracystic nodules in 67.9% of RCCs. Therefore, we tried to develop a diagnostic tree model that included several imaging features because differential diagnoses are sometimes inconclusive with only 1 or 2 imaging findings. By applying the diagnostic tree model, we were also able to attain high diagnostic accuracy in the validation group (91.7%).¹

Dr Bonneville also raised concerns about applying the diagnostic tree to subcentimeter lesions. In our study, we included cystic pituitary adenomas and RCCs that were confirmed histopathologically. Small asymptomatic RCCs showing typical imaging features were not treated surgically; therefore, they were not included in our study. Although this omission can be considered a limitation of our study, we think that preoperative differentiation between cystic adenoma and RCC is important in patients who are considered for surgery due to hormonal or nonhormonal symptoms because different surgical procedures are required according to the different diagnoses. The diagnostic tree model may provide guidance to neurosurgeons for appropriate surgical planning.

We agree with Dr Bonneville that intrasellar pituitary adenoma can show mass effects such as a bulging sellar diaphragm and erosion of the body contours of the sella,⁴which we did not include in our diagnostic tree. Therefore, further studies that add these imaging features to the diagnostic tree model will be helpful in the differential diagnosis of cystic pituitary adenoma and RCC.

References

1. Park M, Lee SK, Choi J, et al. Differentiation between cystic pituitary adenomas and Rathke cleft cysts: a diagnostic model using MRI. AJNR Am J Neuroradiol 2015;36:1866–73
2. Mehta GU, Jane JA Jr.. Pituitary tumors. Curr Opin Neurol 2012;25:751–55
3. Nishioka H, Haraoka J, Izawa H, et al. Magnetic resonance imaging, clinical manifestations, and management of Rathke’s cleft cyst. Clin Endocrinol (Oxf) 2006;64:184–88
4. Bonneville JF, Bonneville F, Cattin F. Magnetic resonance imaging of pituitary adenomas. Eur Radiol 2005;15:543–48

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