What is the first line of imaging for suspected postpartum glomerulonephritis (PPGN)?

First-Line Imaging for Suspected PPGL

For suspected pheochromocytoma/paraganglioma (PPGL), biochemical testing precedes imaging, but once biochemical confirmation is obtained, CT abdomen and pelvis with IV contrast is the first-line anatomical imaging modality.

Important Clarification

The provided evidence addresses acute pyelonephritis and postpartum glomerulonephritis, not pheochromocytoma/paraganglioma (PPGL). These are entirely different clinical entities requiring different diagnostic approaches.

Standard Approach to PPGL Imaging

Initial Biochemical Confirmation Required

• Imaging should never be performed before biochemical confirmation of catecholamine excess, as incidental adrenal masses are common and imaging-first approaches lead to unnecessary procedures and patient anxiety
• Plasma or 24-hour urine metanephrines must be elevated before proceeding to anatomical imaging

First-Line Anatomical Imaging: CT with Contrast

• CT abdomen and pelvis with IV contrast is the preferred initial anatomical imaging for localization once biochemical diagnosis is established
• CT provides excellent spatial resolution for detecting adrenal and extra-adrenal tumors
• Sensitivity approaches 90-95% for adrenal pheochromocytomas
• Must include entire abdomen and pelvis to detect paragangliomas along the sympathetic chain from skull base to pelvis

Critical Pitfalls to Avoid

• Never give IV contrast without adequate alpha-blockade - unblocked patients can develop hypertensive crisis from catecholamine release triggered by contrast
• Ensure patients are on phenoxybenzamine or doxazosin for at least 7-14 days before contrast-enhanced imaging
• If alpha-blockade is contraindicated or inadequate, proceed directly to MRI without gadolinium or use non-contrast CT

Alternative and Complementary Imaging

• MRI abdomen and pelvis is an excellent alternative, particularly in:
  • Pregnant patients (without gadolinium)
  • Patients with contrast allergies
  • Young patients to minimize radiation
  • Paragangliomas (which show characteristic T2 hyperintensity - "light bulb sign")
• Functional imaging with ¹²³I-MIBG or ⁶⁸Ga-DOTATATE PET/CT is reserved for:
  • Metastatic disease detection
  • Extra-adrenal or multifocal disease
  • Hereditary syndromes
  • Recurrent disease
  • Not first-line for initial localization

Imaging Algorithm

1. Confirm biochemical diagnosis first (plasma/urine metanephrines)
2. Initiate alpha-blockade (phenoxybenzamine or doxazosin)
3. Perform CT abdomen/pelvis with IV contrast after adequate blockade (7-14 days)
4. If CT negative but biochemistry strongly positive, proceed to MRI or functional imaging
5. Consider functional imaging upfront in hereditary syndromes or suspected metastatic disease

---

Note: The evidence provided in this query pertains to renal pathology (pyelonephritis and glomerulonephritis), not PPGL. The above recommendations are based on standard endocrine tumor imaging protocols, as the provided evidence is not applicable to the PPGL question.