Frontal Lobe Herniation and New Chiasmopathy: Rare Complications of Dopamine Agonist Therapy in Large Prolactinomas

Dopamine agonists (DA) are first line treatment for prolactinomas. Optic chiasm herniation can rarely occur during therapy, while brain herniation is very uncommon.

Case Description:

A 34 yo W presented with oligomenorrhea and galactorrhea 8 years prior. She received intermittent cabergoline (CAB) for the first 4 yrs. She sought attention for headaches (HA) and vision changes (left sided homonymous hemianopsia). Testing indicated a prolactin (PRL) of 4300ng/mL and a 4x3.9x4.5 cm pituitary adenoma, Knosp 3A with chiasm compression. After 2 weeks of CAB 0.5mg twice a week PRL decreased to 1142ng/mL. CAB was increased to 0.75mg twice a week and PRL decreased to 201ng/mL after 3 months. MRI at this time showed a 4x3.5x3.2cm mass (~ 30% reduction) with medial temporal lobe herniation and encephalocoele. The patient had improvement in HA and subjectively stable vision. CAB was stopped for 3 weeks and she underwent surgical debulking and encephalocoele repair. Postoperative MRI showed a 3.2x3.7x4.5cm mass with surgical debulking of sphenoid sinus component, but superior growth. Histopathology confirmed Pit1 positive PRL tumor without increase in proliferation markers. CAB 0.75 mg twice a week was resumed.

A 50 yo M had incidental detection of a sellar mass after trauma. CT showed 3.7x3.9x3.8cm mass and PRL was 10,008ng/mL. He received bromocriptine 2.5mg daily for 3 months and was lost to follow-up. He presented to our institution 9 months later, without HA or vision changes. Mass was 3.6x3.4x3.6cm, Knosp 3A with minimal contact of right optic nerve. PRL 3,318 ng/ML. He received CAB 0.5mg twice a week with PRL improvement to 26ng/mL after 1 month. After 2 months ophthalmology exam showed new left superotemporal depression. PRL was 68ng/mL and MRI showed 35% mass reduction and new inferior displacement tethering of the chiasm. The patient reported mild HA and no subjective vision loss. After consultation with neurosurgery CAB dose was decreased to 0.25mg twice a week with plan for 3-month MRI and ophthalmology follow-up.

Discussion:

Chiasmal herniation as a consequence of DA therapy has been reported in large macroprolactinomas with significant PRL elevation. Options for treatment include chiasmapexy or DA dose reduction with close visual field and imaging follow-up. Frontal lobe herniation has been rarely reported, with only 6 cases identified. We report the first case of temporal lobe herniation. A rapid biochemical response in large tumors seems to increase risk of chiasmal and lobe herniation. Multidisciplinary approach (surgery, ophthalmology and endocrinology), close follow-up and individualized management are important in these cases.