When confronted by a lesion eccentric to the fossa, what structure is a useful guide to normal but displaced pituitary tissue?
The posterior pituitary bright spot can often be identified. In this case it is elevated and displaced anteriorly.
What is the most likely diagnosis?
A partially sclerotic mass probably arising from, but certainly invading, the skull has a differential which includes metastatic disease (most likely, especially breast cancer), and osteosarcoma. Sinonasal carcinoma with dystrophic calcification or chondrocarcinoma are other possibilities, but less likely.
There is a heterogeneous non-expansive of mass centred on the floor of the pituitary fossa / superior clivus,extending into the posterior sphenoid sinus. The central portion of this mass within the sinus measures 21 x 13 mm in the sagittal plane. This is associated with diffuse pachymeningeal thickening in the prepontine cistern, up to 4 mm thick and extending into the dorsum sella. Normal pituitary tissue is elevated by the mass.
There is in addition, unusually low signal in the marrow cavity of the skull vault, without enhancement. This is a non-specific feature which could represent red marrow regeneration.
In the cerebral parenchyma, there are numerous small T2 hyperintense fossa in the subcortical white matter of both cerebral hemispheres. This is more than would be expected age and could represent chronic microvascular ischaemia or gliosis. None of these lesions demonstrate enhancement or restricted diffusion. No vasogenic oedema is seen. The ventricles and sulci is normal in size of each.
The mastoid cells are fluid filled. There is moderate erosion on the left mandibular condyle evidence of temporomandibular joint synovitis, consistent chronic degenerative joint disease.