Exploring the ‘pars intermedia’: the Rathke’s cleft cyst

A 42-year-old woman presents with intermittent headaches and persistent thirst, as well as increased trips to the bathroom. The ophthalmological assessment was normal and no visual field defects were detected. After a vasopressin (DDAVP) challenge test, central Diabetes Insipidus is suspected and brain MRI is ordered to rule out pituitary lesions.

A dynamic contrast-enhanced MRI examination of the pituitary region is performed with small field of view (FOV) targeting the sella and revealing a midline intra and suprasellar cystic lesion with solid component (arrow). Although the patient did not refer any visual disturbance, it is worth noting the compression of the optic chiasm by the lesion.

The lesion shows slight hyperintensity on T1W sequences with T2W isointensity in the solid component demonstrating significant high T2W signal in the cystic part of the lesion. No significant contrast enhancement was demonstrated along the dynamic study.

A ‘pars intermedia’ or Rathke’s cleft cyst is a common, midline, non-neoplastic and usually incidental sellar or suprasellar lesion proceeding from the embryological remnants of Rathke’s pouch in the hypophysis. These lesions show female predilection (2:1 female to male ratio) and can be found in 11-22% of autopsies [1].

Generally found in adults, the most common clinical presentation includes headaches, pituitary hormonal disturbances and visual abnormalities [2].

From the imaging perspective on MRI, Rathke’s cleft cysts can be either hyper or hypointense on T1W sequences depending on its proteinaceus content [2]. On T2W sequences, the lesion will demonstrate hyperintensity (70%), which can vary relying on cyst’s composition (serous or mucoid) with no contrast enhancement on T1W post-contrast sequences although the surrounding pituitary parenchyma may appear as a thin enhancing rim [3] (arrowhead).

An intracystic solid nodule or ‘intracystic dot’ (arrow), as it is sometimes referred to, can be seen in 65-70% of cases, which usually is hyperintense on T1 and iso-hypointense on T2W sequences compared to the surrounding fluid [4].

Surgical excision is indicated in symptomatic cases, although a recurrence rate of up to 18% may be possible [5]. In this case, the patient refused surgical treatment preferring non-invasive management with Desmopressin and routinary MRI follow-up.