DISCUSSION
Pheochromocytoma is a rare cause of hypertension during pregnancy
occurring only in 1 in 50,000 cases and may be clinically challenging to
differentiate from preeclampsia because hypertension and headache occur
with both disorders. It is a catecholamine-producing tumor arising from
chromaffin cells of medullary region of adrenal gland or sympathetic
ganglia. Symptoms specific to pheochromocytoma include paroxysms of
generalized sweating, palpitations, tremor, pallor, shortness of breath,
generalized weakness, and panic attack-type symptoms. Some women with
pheochromocytoma have an elevated blood glucose level (impaired fasting
glucose, apparent type 2 diabetes mellitus). Our patient had an atypical
presentation which was right flank pain. She also developed seizures
which is one of the uncommon presentations of pheochromocytoma. Overall,
antenatal diagnosis of the condition is crucial because intrapartum
maternal and fetal mortality are high without appropriate treatment5 .
While the diagnosis of preeclampsia may overlap with pheochromocytoma
presenting in pregnancy, the distinguishing feature is that preeclampsia
usually develops after 20 weeks gestation and is associated either with
proteinuria or evidence of end-organ damage whereas pheochromocytoma may
present at any time throughout the entire pregnancy and is rarely
associated with proteinuria 6 . In this case,
the patient presented late in pregnancy, around 35 weeks gestation, her
24-hour urine collection was negative for proteinuria and her
investigations did not show any evidence of end-organ damage.
A review of literature has shown that 10% of pheochromocytomas are
bilateral, 10% of them are extra-adrenal in origin and 10% are
malignant. They may be part of multiple endocrine neoplasia (MEN type
IIa) syndrome and, if it is the case, the patient should be screened for
medullary cell carcinoma of the thyroid and parathyroid adenomas by
measuring serum calcitonin and parathyroid hormone (PTH) levels
respectively 7 . Our patient’s tumor was
unilateral (right side), adrenal in origin and benign in nature, as per
postoperative histopathological examination. MEN syndrome was ruled by
taking the patient’s past medical and family histories.
The diagnosis of pheochromocytoma is made by the detection of elevated
24-hour urinary levels of catecholamines (norepinephrine, metanephrines
and vanillylmandelic acid) and/or raised plasma catecholamines.
Non-specific assays may give false-positive results if the patient is on
alpha-methyldopa or labetalol and screening should ideally be performed
before antihypertensive therapy is started. Once the diagnosis has been
confirmed, CT, ultrasound and MRI offer the best methods for localizing
the tumor, although the latter two are preferable in pregnancy. However,
MIBG (131I-meta-iodobenzylguanidine) scan to localize norepinephrine
uptake is contraindicated in pregnancy 8 .
When pheochromocytoma presents in pregnancy, there is a greatly
increased maternal and fetal mortality rate, especially if, as in up to
50% of cases, the diagnosis is not made antenatally, as potentially
fatal hypertensive crises may be precipitated by labor, vaginal or
abdominal delivery, general anesthesia or opiates. Hypertensive episodes
may occur in pregnancy even when patient is in supine position owing to
the pressure caused by the gravid uterus on the tumor. The main causes
of maternal mortality are arrhythmias, cerebrovascular accidents or
pulmonary edema. Its rate may reach up to 17% in undiagnosed cases
while it is only about 4% in diagnosed cases. On the other hand, the
perinatal mortality rate is about 26% in undiagnosed cases and 11% in
diagnosed cases 9 .
The only curative option for pheochromocytoma is surgical removal of the
tumor, either open or laparoscopic. The optimal timing for that depends
on the gestational age at which the diagnosis is made. There is an
increasing vogue to delay tumour resection until the puerperium. If
pharmacological blockade, ideally with α-blockade with phenoxybenzamine,
prazosin or doxazosin to control hypertension followed by β-blockade, if
required, to control tachycardia, has been achieved prior to 23 weeks’
gestation, then resection may be performed in pregnancy especially if
the tumor is small. If the pregnancy is more than 24 weeks’ gestation,
then surgery becomes more hazardous and should be delayed until fetal
maturity, when caesarean section with concurrent or delayed tumour
removal is undertaken 10 .
Expert anaesthetic care is necessary in dealing with these cases and
both perinatal and maternal mortality rates have improved significantly
since the advent of α-blockade, which should be given for at least 3
days prior to the surgery. IV Phenoxybenzamine must be available for
caesarean section. In an emergency if IV α-blockade is not available,
then IV labetalol is the appropriate alternative11 .