Chiasmal injury in silent pituitary apoplexy without evidence of mass effect

Case 1: A 69-year-old male presented with a 2-year history of progressive blurry vision in the left eye and pain in the left side of his face and forehead. An MRI of the orbits showed an empty sella and a 4.1 x 2.0 x 1.7 cm mass in the left middle cranial fossa lateral to the cavernous internal carotid artery and abutting the left optic nerve (Fig 1a). Initial review of the MRI suggested a normal optic chiasm. Prolactin was found to be elevated at 2815 ng/mL, and the patient was started on cabergoline for prolactinoma. Visual field testing conducted 2 months after initial presentation showed incomplete temporal field loss in the right eye as well as complete temporal field loss in the left eye (Fig 1b). Optical coherence tomography (OCT) revealed nasal ganglion cell complex (GCC) thinning in the right eye and diffuse GCC thinning in the left eye (Fig 1c). This chiasmal pattern of visual field defect and right eye optic nerve damage which were not expected to be affected by the left cranial fossa lesion, prompted repeat imaging of the optic chiasm. A second MRI of the brain performed 4 months after the first showed that the chiasm was distorted with downward displacement, and revealed that the sella contained a tumor-associated cyst (Fig 1d). Although the mass, which was now displaying small areas of liquefactive necrosis, extended to the left superior orbital fissure and displaced the native pituitary gland rightward, it did not appear to be exerting a mass effect on the optic chiasm or tract. Although the patient had received cabergoline between these two MRIs, repeat evaluation of the first MRI showed similar observations of a “sagging” optic chiasm without evidence of mass effect (Fig 1e), indicating that this finding was not a result of treatment.

Fig 1.

Case 1. A: Initial T1-weighted axial MRI. B: 30-2 Humphrey visual field testing. C: Ganglion cell deviation maps on macula OCT. D: Follow-up T1-weighted coronal MRI. E: Initial T1-weighted coronal MRI.

Case 2: A 44-year-old male presented following an incidental finding of a pituitary mass on a CT scan performed for dental evaluation. MRI of the brain showed an expanded sella containing a T2 hyperintense 1.6 x 1.0 cm mass with liquefactive necrosis, abutting the medial aspects of the internal carotid arteries bilaterally (Fig 2a). Like the previous case, the initial read of the MRI reported no compression of the optic chiasm. The patient did not report any vision loss and had normal visual fields (Fig 2b), however, on macula OCT he had focal superonasal GCC thinning in the right eye and mild nasal GCC thinning in the left eye (Fig 2c), consistent with pre-perimetric ganglion cell injury in a chiasmal pattern. A second MRI 4 months later also showed that no elements of the patient’s mass were in contact with the chiasm. On further review both MRIs revealed downward displacement of the chiasm (Fig 2d).

Fig 2.

Case 2. A: Initial T1-weighted coronal MRI. B: 30-2 Humphrey visual field testing. C: Ganglion cell deviation maps on macula OCT. D: Follow-up T1-weighted coronal MRI.

Interpretation of findings

Here we report two cases of pituitary adenoma with MRI showing unexplained sagging or downward displacement of the optic chiasm, without the chiasm coming into contact with the tumor, along with evidence of chiasmal injury on ophthalmic imaging. Nasal GCC thinning on macula OCT confirmed chiasmal injury in both these cases, and visual field deficits in one case. In both these cases imaging demonstrated evidence of either hemorrhage or necrosis as well as cystic components in the pituitary masses, which is radiological evidence of previous hemorrhage¹. These patients likely experienced asymptomatic or silent pituitary tumor apoplexy, leading to regression of a portion of the mass that was previously compressing the chiasm.

Pituitary apoplexy is a clinical syndrome involving either hemorrhage or infarction of a pituitary tumor, which classically presents with a severe acute headache, nausea and visual deficits². However, several studies have found that the majority of cases involving either radiographic or surgical evidence of hemorrhage or infarction of a pituitary tumor were not associated with these symptoms^1,3. This asymptomatic presentation is known as silent or subclinical apoplexy (SPA).

Visual impairment is a leading presenting symptom in patients with SPA. Zhang et al. reported visual disturbances in 142 of 185 SPA patients, of which 46 had visual field defects⁴. Liu et al. also described visual deficit as being a common symptom, present in 70% of cases in another cohort of SPA patients³. Although there have been accounts of such silent pituitary apoplexy presenting with chiasmal injury and bitemporal hemianopia, this is to our knowledge the first report presenting MRI findings of a deviated chiasm without apparent involvement by a mass. Such downward herniation of the chiasm has also been reported to occur following surgical resection of pituitary adenomas⁵. In our two cases, it cannot be determined whether the chiasmal compression occurred because of mass effect prior to apoplexy or the apoplexy event itself. This distinction is significant because acute visual impairment due to apoplexy can often be reversed with surgical removal of the hemorrhage⁶. Our patients were not considered surgical candidates because of the delay between the suspected time of apoplexy and neuroimaging. Nevertheless, these cases demonstrate that pituitary apoplexy should be considered in cases of MRI findings of chiasmal abnormality or clinical evidence of chiasm dysfunction in the setting of known pituitary adenoma. In addition, this case highlights the importance of correlating brain imaging, ophthalmic imaging, and visual testing in cases of suspected chiasmal injury, especially when chiasmal abnormality on MRI is subtle.