When Renal Colic Isn’t Renal Colic: Ruptured Abdominal Aortic Aneurysm Masquerading as Flank Pain

Abstract

Abdominal pain remains one of the most diagnostically challenging presentations in emergency medicine. Although flank pain, dysuria and vomiting commonly suggest renal issues, clinicians must remain vigilant for time-critical vascular emergencies that mimic these conditions.

An independent woman in her seventies with a background of hypertension presented to the emergency department with sudden left flank pain, vomiting, and dysuria. The pain had initially resolved with paracetamol before recurring several hours later. She denied fever, haematuria, or bowel symptoms. As her observations were initially reassuring and she was pain-free at triage, she was allocated Australasian Triage Scale category 3.

Approximately 45 minutes later, medical review identified profound hypotension, with a systolic blood pressure of 82 mmHg, prompting immediate transfer to the resuscitation area. Aggressive intravenous fluid resuscitation was commenced, and routine bloods and urine were sent. Initial venous blood gas analysis demonstrated acute kidney injury, with an estimated glomerular filtration rate of 32 mL/min/1.73 m², and hyperlactataemia of 3.9 mmol/L. Emergency department examination revealed marked tenderness and rigidity to the left of the umbilicus, while renal angle tenderness was absent. Subsequent review by the acute surgical team demonstrated a soft, non-tender abdomen. Despite initial resuscitation, repeat venous blood gas analysis demonstrated a rising lactate of 4.6 mmol/L, indicating worsening tissue hypoperfusion.

The differential diagnosis shifted dramatically from renal colic to catastrophic intra-abdominal pathology, including mesenteric ischaemia, ruptured abdominal aortic aneurysm (AAA), bowel perforation, and obstructive uropathy complicated by sepsis. The patient subsequently developed recurrent hypotension and oxygen desaturation to 88%. Despite concerns regarding iodinated contrast in the setting of impaired renal function, the immediate threat to life outweighed the risk of contrast. Following discussion with radiology, urgent contrast-enhanced CT abdomen and pelvis with CT mesenteric angiography was performed. CTPA was added because of concurrent hypoxaemia to exclude pulmonary embolism and left lower lobe pneumonia.

Imaging confirmed the diagnosis: ruptured abdominal aortic aneurysm.

This case highlights the enduring importance of repeated bedside assessment and clinical judgement. Hypotension, rising lactate, and evolving abdominal findings should never be dismissed, even when the initial presentation appears consistent with a common diagnosis. A normal or reassuring examination by another clinician should not override persistent concern when objective markers indicate deterioration.

In elderly patients presenting with flank or abdominal pain, those with vascular risk factors such as hypertension—ruptured AAA must always remain a critical differential diagnosis, as early recognition and expedited imaging are pivotal to improving survival.