Inferior petrosal sinus sampling

Inferior petrosal sinus sampling is an infrequently used method of confirming the presence of a hormonally active pituitary microadenoma, when imaging alone has been insufficient. This technique is able to confirm that excess hormone (e.g. ACTH) is being produced by the pituitary and may also help in lateralising the microadenoma (although the later is more contentious). 

Indication

Inferior petrosal sinus sampling is most frequently indicated when patients have confirmed ACTH dependent  Cushing's syndrome. ACTH secreting pituitary microadenomas, which may be inapparent on imaging in 40 to 50% of cases, account for 80% of non-adrenal, non-iatrogenic cases.  

Technique

Although technique varies a standard modern approach would consist of:

1. review prior imaging to try and identify inferior petrosal sinus anatomy
2. bilateral common femoral vein punctures with guiding catheter / microcatheter/microcatheter set-up
   • one sheath should be oversized to allow for peripheral venous sampling, or alternatively a peripheral IV can be located and a non-scrubbed assistant can withdraw the peripheral sample.
3. heparin: given the length of time catheters remain in situ, heparin is administered to prevent venous sinus thrombosis. Typically 5,000 unit bolus⁵.
4. once a catheter is located in the jugular bulb rapid injection of contrast is performed to attempt to reflux contrast into the inferior petrosal sinus to guide placement of a microcatheter
   • if access to the sinus is difficult then an arterial puncture can be performed to enable a common carotid injection and road mapping of the IPS
   • it is important to note that in ~7% of patients the inferior petrosal sinus does not drain into the jugular bulb, but rather directly into the vertebral venous plexus ⁴
5. each sinus is catheterised with the microcatheter, a similar distance from the gland
6. baseline samples are obtained (one or two sets) simutaneously from both catheters and the periphery
7. corticotrophin-releasing hormone (CRH) is administrated (100 mg IV⁵).
8. sequential simultaneous samples (e.g. at 3, 5, 10 and 15 minutes) are then obtained.
   • one of the greatest pitfalls is mislabeling the numerous samples. Ideally 5 personel are required. Three to aspirate, one to transfer into the EDTA tubes and another to keep track of time etc...
9. submit samples for laboratory assays.

Interpretation of results

IPSS is a highly sensitive and specific examination series reporting near 100% values for both. Exact ratio values will vary between institutions. Typical published ratios are:

• Pre CRH
  • > 1;1.7 : 1:1 central : peripheral:peripheral = pituitary source
  • < 1;1.5 : 1:1 central : peripheral:peripheral = ectopic source
• Post CRH
  • > 3;3.3 : 1:1 central : peripheral:peripheral = pituitary source
  • < 1;1.8 : 1:1 central : peripheral:peripheral = ectopic source
• Lateralisation
  • > 1;1.4 : 1:1 interpetrosal gradient

Complications

Complications are rare, but reported, and include:

• deep cerebral venous thrombosis
• pulmonary embolism
• venous subarachnoid hemorrhage (SAH)
• brain stem ischaemic injury

In a large review of 508 patients ² a single complication was observed (0.2%), although a conservative 1% incidence of serious complications has been suggested be quoted.