Eval for VP shunt malfunctions

[migm]

Hi guys,

Graduating ED resident here. Had a question about VP shunt taps and their interpretation. I recently had a patient with some transient 3rd ventricular enlargement but subsequent persistent symptoms of Paranauds. An MRI was obtained and did not show evidence of parenchymal disease. A VP shunt had recently been placed and a tap was performed. Opening pressure was zero mmhg however flow was observed. The shunt was initially not felt to be the cause of her dorsal midbrain syndrome, but later on was felt to be at blame as no other cause was identified. She underwent EVD then revision and her symptoms resolved. So my question to you is, can you help me interpret what a tap with flow of 0 mm means? I understand that decreased flow likely lends itself to a proximal limb or possibly a reservoir problem, but what does it mean in the setting of flow? is this normal, reassuring? Why isn't the OP higher?

Thanks y'all
migm

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[neusu]

Hi guys,

Graduating ED resident here. Had a question about VP shunt taps and their interpretation. I recently had a patient with some transient 3rd ventricular enlargement but subsequent persistent symptoms of Paranauds. An MRI was obtained and did not show evidence of parenchymal disease. A VP shunt had recently been placed and a tap was performed. Opening pressure was zero mmhg however flow was observed. The shunt was initially not felt to be the cause of her dorsal midbrain syndrome, but later on was felt to be at blame as no other cause was identified. She underwent EVD then revision and her symptoms resolved. So my question to you is, can you help me interpret what a tap with flow of 0 mm means? I understand that decreased flow likely lends itself to a proximal limb or possibly a reservoir problem, but what does it mean in the setting of flow? is this normal, reassuring? Why isn't the OP higher?

Thanks y'all
migm

I'd have to see the details of the case. If the proximal tubing is patent, but restricted at some point, it may still have flow and low pressure in the shunt system but elevated pressure in the ventricles (think different sbp in right and left arms in aortic stenosis or dissection). Alternatively, user error on the tap and interrogation. Shunts are notoriously difficult to interpret.