It’s well known that if a CNS lymphoma is suspected, administration of corticosteroids therapy should be delayed until a definitive biopsy has been performed.

The differential diagnosis of a hypothalamic mass includes craniopharyngioma, Rathke cleft cyst, germ cell tumour, granulomatous processes, glioma, hamartoma, germinoma and aneurysm (Samuels and de la Monte 1994; Akhaddar et al. 2001, 2011; Oweity et al. 2002; Chourmouzi et al. 2005; Binning et al. 2008; Rennert J and Doerfler 2007; Raoa et al. 2008; Fadoukhair et al. 2010; Belfquih et al. 2012).

Craniopharyngioma has a heterogeneous appearance with solid and cystic elements tumour in the suprasellar region. Rathke cleft cysts usually have the following imaging features: a sellar epicentre, smooth contour, lack of calcification, lack of internal enhancement and a homogeneous signal intensity within the lesion. The characteristic features of granulomatous diseases are thickening of the pituitary stalk and absence of a normal bright posterior pituitary signal. Imaging of germ cell tumour shows generally an infiltrative, solid, homogeneous mass in the midline with intense contrast enhancement. Hypothalamic glioma tends to be solid with microcyst formation and is iso- or hypointense on T1-weighted images, hyperintense on T2-weighted images and demonstrates enhancement with contrast. Hypothalamic hamartoma presents as precocious puberty in a young child with a nodular mass in the suprasellar cistern. The mass is isointense with normal brain on T1-weighted images and isointense or mild hyperintense on T2-weighted images. These lesions usually do not enhance after contrast administration. Suprasellar germinoma appears as a well-marginated lobulated homogeneous tumour with prolonged T1 and T2 relaxation times which strongly enhances after gadolinium administration. The presence of these imaging findings along with the presence of diabetes insipidus and a suprasellar mass is a clue to the diagnosis of germinoma. Although metastatic tumour could not be ruled out, absence of any primary malignancy on chest, abdominal and pelvic computed tomography scan (CT scan) made it unlikely. Aneurysms of the sellar region usually originate from the cavernous or supraclinoid portions of the internal carotid artery and account for up to 10 % of all cerebral aneurysms. In selected cases, they can mimic other supra-, para- or intrasellar lesions. MRI or CT scan is useful in differentiating tumour from thrombosed and nonthrombosed aneurysms.

The differential diagnosis of primary versus secondary CNS lymphomas may include a complete neurological staging, including cerebrospinal fluid examination and ophthalmological evaluation with slit-lamp examination to exclude vitreous or retinal involvement. In addition, an abdominopelvic CT scan and bone marrow biopsy may be obtained to exclude systemic lymphoma (Giustina et al. 2001).