Bilateral inferior petrosal sinus sampling (BIPSS) is the gold standard test for distinguishing Cushing's disease from ectopic ACTH syndrome. It involves catheterizing the bilateral petrosal sinuses and sampling blood at baseline and after stimulation with CRH or desmopressin. The diagnostic accuracy for localizing the source of ACTH is well established, but ability to lateralize pituitary tumors is limited. Using a prolactin-adjusted IPS:P ACTH ratio can improve differentiation between central and ectopic sources and may help with lateralization. Anatomical variations can impact accuracy, and a technically skilled interventional radiologist is needed.

1. Inferior Petrosal Sinus
Sampling

3. • Bilateral inferior petrosal sinus sampling (BIPSS) is a gold standard test to distinguish between
Cushing’s disease (CD) and ectopic adrenocorticotropic hormone (ACTH) syndrome.
• The diagnostic accuracy of BIPSS in localizing ACTH source is well established, but its ability to
lateralize side of corticotropinoma in pituitary is limited.
• IPSS is a technically challenging procedure and should be performed by
an experienced interventional or neuroradiologistInferior petrosal sinus
sampling often performed under local anesthesia.
• The femoral veins are cannulated and microcatheters are placed in the
bilateral petrosal sinuses under fluoroscopic guidance.

4. • Venous angiography is used to confirm correct catheter placement,
as demonstrated by retrograde flow of contrast into the
contralateral cavernous sinus.
• Simultaneous venous blood samples are obtained from the petrosal
sinuses and a peripheral vein.
• The blood samples are drawn at baseline and then at 2, 5, 10, and
15 minutes following CRH (1 μg/kg, maximum 100 μg) or vasopressin
(10 μg) administration.

5. • perform IPSS before starting any antihypercortisolemic therapy
• patient on antihypercortisolemic therapy needs IPSS- stop the
medication and schedule the procedure once confirm
hypercortisolemia on biochemical testing.

7. • Some centers use DDAVP (desmopressin) for IPSS because of lower
cost and unavailability of CRH.
• DDAVP stimulates ACTH production via the V2R receptor subtype on
corticotroph adenomas and elicits a response similar to CRH .
• Deipolyi et al. showed comparable diagnostic results using
identical IPS:P ACTH gradients after DDAVP and CRH stimulation
• Tsagarakis et al. demonstrated good IPSS sensitivity and
specificity in 54 patients following administration of combination
CRH and DDAVP .

10. lower accuracy of BIPSS
• Variable venous drainage
• catheter misplacement
• improper sampling
• cyclicity of disease
• mild CD
• low responsiveness to CRH stimulation
• patients on medical therapy can lead to lower accuracy of BIPSS.

11. prolactin-adjusted IPS:P ACTH
ratio
• Growth hormone, thyroid-stimulating hormone, α-subunit of human
chorionic gonadotropin, and prolactin have been measured to assess
catheter placement during IPSS.
• Prolactin is an abundant pituitary hormone least affected by cortisol,
used reliably for success of catheter placement in petrosal sinus, and
prolactin-adjusted ACTH ratio is used to improve its diagnostic
accuracy in lateralizing adenoma.
• Some studies have shown improved accuracy of prolactin-adjusted
ACTH ratios for tumor localization during BIPSS.

12. • improve differentiation between CD and ectopic ACTH syndrome in
the absence of proper IPS venous efflux.
• Findling and colleagues used prolactin as an index of pituitary
venous efflux in 3 cases of surgically proven CD in whom IPSS
failed to demonstrate an appropriate IPS:P ACTH gradient (and an
ectopic source could not be found).
• The authors showed that a prolactin-adjusted IPS:P ACTH ratio
(dominant post-CRH IPS:P ACTH/ipsilateral pre-CRH IPS:P prolactin)
> 0.8 would have identified these 3 patients as having CD. The
ratio was < 0.6 in 5 EAS patients.

14. Anatomical variations
• The anterior pituitary drains from the cavernous into the inferior petrosal
sinuses.
• The inferior petrosal sinuses course posterior and caudal and enter the jugular
veins at the skull base .
• It is not uncommon to have unequal drainage of the cavernous sinuses. Some
literature suggests this anatomical variant may be present in 40% of individuals
• There are other aberrations that make analysis much more difficult.
The most notable variants are as follows:
(1) inferior petrosal anastomosis to vertebral venous plexus;
(2) no connection between the inferior petrosal sinus and the jugular vein; and
(3) a hypoplastic inferior petrosal sinus .

15. Previous studies have suggested that microcatheters can be used to
obtain accurate venous sampling if abnormal anatomy is known or
suspected.
It is also possible to obtain a direct sample from the cavernous
sinuses, but this approach has not proved superior to IPSS
The literature indicates that the prevalence of IPS abnormalities
exceeds that of false-negative IPSS results, meaning that adequate
catheterization is most often feasible.

17. • They diagnosed CD using a prolactin-adjusted IPS:P ACTH
ratio ≥ 1.3. All ratios ≤ 0.8 corresponded to ectopic
ACTH syndrome. Prolactin-adjusted IPS:P ACTH ratios
ranging from 0.8 to 1.3 did not discriminate between CD
and ectopic ACTH syndrome.
• The authors concluded that a prolactin-adjusted IPS:P
ACTH ratio of: (1) ≤ 0.8 suggests EAS; (2) ≥ 1.3
indicates CD; and (3) 0.8 to 1.3 needs further
investigation . These findings are similar to those of
Grant et al .
• The use of the prolactin-adjusted ACTH ratio has
potential limitations. The pre-CRH prolactin value does
not account for erroneous IPS sampling that may occur
after CRH injection because of repositioning of the
catheter tip.
• It is also possible that the prolactin-adjusted IPS:P
ACTH ratio in ectopic ACTH syndrome may mimic CD if
there is unsuccessful IPS cannulation

18. • In case 2, using the baseline sample at -10
minutes, the prolactin-adjusted IPS:P ratio is
0.77 and below the threshold of 0.8, which
could indicate an ectopic source. If we use the
second pre-CRH prolactin value (drawn at the -5
minute timepoint), then the ratio further
decreases to 0.63 (very close to the 0.6 cutoff
suggested by Findling et al.)
• Larger studies are needed to confirm the role
of the prolactin-adjusted IPS:P ACTH ratio in
ACTH-dependent CS and failed IPS cannulation.

19. • What is the value of the intersinus ACTH ratio in tumor lateralization?
• An intersinus ACTH gradient > 1.4 has limited value in predicting
tumor lateralization (8).
• There are limited data on the use of IPSS to lateralize pituitary
adenomas. In 1985, Oldfield and colleagues proposed an intersinus
ACTH gradient of > 1.4 (before CRH administration) for ipsilateral
lateralization of pituitary tumors (8). This ratio has proven less
reliable as more data have emerged, including a large series of
501 patients published by NIH in 2013 (62). The literature reports
correct tumor lateralization using this ratio in 50% to 70% of
cases (62, 67-69). There is no evidence to suggest that
lateralization improves following CRH administration. In later
work from the NIH by Wind et al., the positive predictive value
(PPV) for accurate lateralization peaked at 86% using an
intersinus ACTH gradient of 60:1. The authors acknowledged,
however, a substantive limitation because only 7% of patients who
had a unilateral adenoma reached this ratio. This same paper
showed that left-sided ACTH lateralization was associated with
greater accuracy (reasons unknown).

20. • The highest level of accuracy was observed in patients who had
consistent lateralization before and after CRH administration
(PPV = 72%). These studies reinforce the need for careful
neurosurgical exploration of the pituitary gland to identify an
adenoma, which may be smaller than 1 mm in the largest diameter .
• This patient’s intersinus ACTH ratio suggested a left-sided
lesion. This was inaccurate. Transsphenoidal exploration revealed
a right-sided adenoma. The surgical pathology confirmed a
corticotroph adenoma.

21. • Does the prolactin-adjusted intersinus ACTH gradient improve lateralization?
• The use of a prolactin-adjusted intersinus ACTH gradient > 1.4
improves corticotroph adenoma lateralization during IPSS.
• There have been several attempts to improve the predictive value
of the intersinus ACTH gradient. In 2012, Mulligan et al. (59)
showed improved adenoma lateralization from 54% to 75% using a
prolactin-adjusted intersinus ACTH gradient of > 1.4 in their
series. The combination of data from pituitary MRI and prolactin-
adjusted intersinus ACTH ratio enhanced the lateralization
concordance to 82% (55). When successful bilateral IPS
catheterization was confirmed using an IPS:P ACTH ratio > 1.3
(n = 14), there were no instances in which the prolactin-adjusted
IPS:P ACTH ratio was associated with a contralateral tumor
(adenoma was either ipsilateral or centrally located) (59). A
later analysis by Qiao et al. again supported improved tumor
lateralization using a prolactin-adjusted intersinus ACTH gradient
(53). They increased their lateralization from 65% to 77% using an
intersinus prolactin-adjusted ACTH > 1.4 following DDAVP
administration. They suggested that anatomical variation (such as
preexisting communication between the cavernous sinuses) might
explain sampling failures

22. • They did not comment on the ability of the
intersinus prolactin-adjusted ACTH ratio to
predict lateralization in patients who had
successful bilateral IPS cannulation based on
the IPS:P prolactin ratio. There are certain
(apparent) situations in which this correction
cannot be applied, including rare cases of
corticotroph hyperplasia and ectopic pituitary
tumors (59). In our patient, the intersinus
prolactin-adjusted ACTH ratio correctly
indicated a right-sided adenoma.

23. • A recent report in the Journal of
Neurosurgery discussed a case of CD in which a
7-tesla (T) MRI was able to localize an
otherwise invisible tumor.
• The authors suggest that 7-T imaging may
preempt IPSS in standard and dynamic contrast
1.5-T and 3-T MRI-negative CD .
• This mirrors a previous study that was able to
detect 3 pituitary adenomas on 7-T MRI unseen
on 1.5-T imaging .

24. • Does the prolactin-adjusted intersinus ACTH gradient improve lateralization?
• The use of a prolactin-adjusted intersinus ACTH gradient > 1.4
improves corticotroph adenoma lateralization during IPSS.
• There have been several attempts to improve the predictive value
of the intersinus ACTH gradient. In 2012, Mulligan et al. (59)
showed improved adenoma lateralization from 54% to 75% using a
prolactin-adjusted intersinus ACTH gradient of > 1.4 in their
series. The combination of data from pituitary MRI and prolactin-
adjusted intersinus ACTH ratio enhanced the lateralization
concordance to 82% (55). When successful bilateral IPS
catheterization was confirmed using an IPS:P ACTH ratio > 1.3
(n = 14), there were no instances in which the prolactin-adjusted
IPS:P ACTH ratio was associated with a contralateral tumor
(adenoma was either ipsilateral or centrally located) (59). A
later analysis by Qiao et al. again supported improved tumor
lateralization using a prolactin-adjusted intersinus ACTH gradient
(53). They increased their lateralization from 65% to 77% using an
intersinus prolactin-adjusted ACTH > 1.4 following DDAVP
administration. They suggested that

25. • anatomical variation (such as preexisting communication between
the cavernous sinuses) might explain sampling failures (53). They
did not comment on the ability of the intersinus prolactin-
adjusted ACTH ratio to predict lateralization in patients who had
successful bilateral IPS cannulation based on the IPS:P prolactin
ratio. There are certain (apparent) situations in which this
correction cannot be applied, including rare cases of corticotroph
hyperplasia and ectopic pituitary tumors (59). In our patient, the
intersinus prolactin-adjusted ACTH ratio correctly indicated a
right-sided adenoma.
• There are 2 recent studies that are less supportive of using the
prolactin-adjusted intersinus ACTH gradient for tumor
lateralization but both are small. De Sousa et al. published a
retrospective review of IPSS lateralization in 13 patients (71).
Their predicted and surgical findings were concordant in only 4
patients regardless of whether the intersinus gradient was
corrected for prolactin. The authors concluded that the adjusted
ratio could not be used because of consistent co-lateralization of
prolactin and ACTH. The study however successfully cannulated both
IPSs in only 7 patients (54%). They did not report separately on
patients who had adequate

26. • sampling and pathology-proven CD (71). A second
paper (72) included only 8 patients, 5 of whom
had an adenoma > 6 mm (for whom IPSS may not
have been indicated). Of the 8 patients, only 1
demonstrated discordant intersinus ACTH and
prolactin-adjusted intersinus ACTH ratios. In
summary, further evaluation of the prolactin-
adjusted ACTH ratio is needed to prove reliable
surgical guidance. A careful surgical
exploration of the entire pituitary gland in
cases where sellar imaging does not reveal a
distinct adenoma is needed.

27. • The role of jugular venous sampling in ACTH-dependent CS
• Internal jugular vein sampling (JVS) has been proposed as an
easier and safer alternative to IPSS (80-83). Unfortunately, JVS
is less sensitive for diagnosing CD than IPSS. Current literature
suggests the sensitivity of JVS ranges from 68.7% to 81.3%
compared with 93.8% to 98% for IPSS (81, 83). There are several
factors that improve JVS sensitivity including: (1) CRH
stimulation; (2) positioning catheters against the medial walls of
the jugular veins close to the IPS origins; and (3) performing a
Valsalva maneuver during the procedure (to facilitate mixing of
blood) (82). Erickson et al. enhanced JVS by adjusting the
reference ratios for interpreting the results (81). They maximized
the sensitivity (as described previously) using a pre-CRH IPS:P
ACTH ratio of 1.59 and a post-CRH IPS:P ACTH ratio of 2.47. They
observed, however, that during simultaneous JVS and IPSS, the
former missed the diagnosis of CD in about 30% of cases (83).
Arguably, JVS is less invasive and may be performed by less
experienced radiologists. That said, if JVS must be substituted
for IPSS, negative results (no central/peripheral gradient) should
prompt referral to a tertiary center for IPSS confirmation. In
most institutions, the only indication for JVS is unsuccessful IPS
cannulation.