Missed Subarachnoid Hemorrhage: The Case That Turns on the History

Somewhere between five and twelve percent of patients with aneurysmal subarachnoid hemorrhage are initially misdiagnosed — sent home from the emergency department with migraine, viral syndrome, or musculoskeletal pain, only to return hours or days later after a rebleed that is often fatal and almost always catastrophic.¹² The imaging has improved, the literature is mature, and the guidelines are clear. The misses, overwhelmingly, are not made at the scanner. They are made at the bedside, in the thirty seconds when the provider decides whether the story the patient is telling is the story of a thunderclap.

The Presentation, Classic and Otherwise

The hallmark of aneurysmal SAH is the thunderclap headache — sudden, severe, reaching maximum intensity within seconds to minutes. Patients classically describe it as the worst headache of their life. Neck stiffness, photophobia, nausea, vomiting, altered consciousness, or focal neurological deficits may accompany it.

Two features of the presentation cause the majority of misses.

The first is the sentinel headache — a warning leak days to weeks before the major hemorrhage, often less severe than the subsequent rupture, frequently self-limited. Up to forty percent of patients with aneurysmal SAH report such a headache on retrospective questioning, yet at the time it is often attributed to migraine, tension headache, or sinus pain, and imaging is not obtained.³

The second is atypical presentation. Some patients arrive with neck pain, syncope, a seizure, or confusion without a prominent headache complaint. Elderly patients, patients with altered mental status, and patients who do not speak English fluently may be unable to give the history the classic teaching demands. Small-volume hemorrhages may produce less dramatic symptoms that read, on first impression, as something benign.

The decisive clinical question is not whether the patient uses the words "worst headache of my life." Many patients will not use that phrase unprompted, and the phrase itself has been overrepresented in the teaching. The decisive question is whether the headache was sudden in onset — reaching peak intensity within seconds to minutes — and whether it was different from the patient's usual headaches. Both features have to be elicited. Neither can be assumed from an unadorned chief complaint of "headache."

The Diagnostic Workup

The standard diagnostic approach for suspected SAH has evolved but remains anchored in a small number of well-established principles.

Non-contrast CT of the head is the initial test of choice. Its sensitivity is highly time-dependent. Within six hours of symptom onset, modern third-generation CT scanners approach ninety-eight to one hundred percent sensitivity for aneurysmal SAH when read by an attending-level reader.⁴⁵ At twelve hours sensitivity falls to roughly ninety-three to ninety-eight percent. At twenty-four hours, ninety to ninety-five percent. Beyond five to seven days, blood is reabsorbed and sensitivity drops substantially. The analytical implication is direct: a negative CT obtained promptly after onset effectively excludes SAH; a negative CT obtained twelve or eighteen hours in does not.

Lumbar puncture is the traditional second step when CT is negative and clinical suspicion persists. The findings that matter are not co-equal. Xanthochromia — yellow discoloration of the CSF from bilirubin, a hemoglobin breakdown product — typically develops two to four hours after hemorrhage and may persist for two to four weeks. It is the most reliable LP marker of true SAH and the one on which a defensible interpretation rests. An elevated red blood cell count is suggestive but must be distinguished from a traumatic tap; the traditional heuristic of comparing RBC counts across sequential tubes is widely taught but has weaker evidentiary support than often presumed.⁶ An opinion that rests heavily on RBC clearance without xanthochromia analysis is vulnerable on cross-examination, and should be.

CT angiography identifies cerebral aneurysms with high sensitivity for aneurysms ≥3 mm. An increasing number of institutions now pursue a "CT plus CTA" pathway in lieu of LP for low-risk patients presenting within six hours, on the strength of studies suggesting that this combination approaches near-complete sensitivity.⁶⁷ The 2012 AHA/ASA Guidelines for the Management of Aneurysmal SAH continue to recommend LP when CT is negative and suspicion persists, and the 2023 Neurocritical Care Society guideline frames the CT-plus-CTA strategy as reasonable in selected contexts rather than as a general replacement.⁸ The decision to forgo LP should be made deliberately, with documented reasoning, and not by default.

Where the Diagnosis Is Missed

Case-series analyses of missed SAH identify a small number of recurring failure points.¹²

• Failure to obtain CT. The headache is attributed to a benign cause without imaging, despite history features — sudden onset, peak within minutes, different from prior headaches — that should have triggered a workup. This is the single most common pathway to a missed diagnosis.
• Failure to perform LP after a negative CT obtained outside the six-hour window. The CT is negative and the patient is discharged. The timing of the scan relative to symptom onset is not accounted for, and the clinical suspicion that would justify the LP is not documented.
• Misinterpretation of LP results. Xanthochromia is not recognized; RBCs are attributed to traumatic tap on weak heuristics; the LP is performed too early, before xanthochromia has had time to develop.
• Inadequate history-taking. The decisive features of the headache — time to peak, comparison to prior headaches, sudden-vs-gradual onset — are not elicited or are not documented. A chief complaint of "headache" is allowed to stand as the operative history.
• Anchoring on an alternative diagnosis. The provider commits early to migraine, tension headache, or viral syndrome, and does not reconsider when the clinical picture is atypical or the patient's response to treatment is unexpected.

These are not separate failure modes. They compound. A history that was not carefully taken produces a differential that does not include SAH; a differential that does not include SAH produces a workup that stops at a CT read outside its window; a workup that stops early produces a chart that does not document the reasoning for stopping.

The Stakes and the Causation Question

The clinical stakes in missed SAH are substantial. A patient with an untreated ruptured aneurysm faces a cumulative risk of rerupture that is highest in the first twenty-four to seventy-two hours — the period in which aneurysm securing, by surgical clipping or endovascular coiling, would have most likely prevented deterioration. Rerupture mortality approaches fifty to eighty percent. Patients who survive the initial event remain at risk for delayed cerebral ischemia from vasospasm in the second week, for hydrocephalus, seizures, and the cascade of medical complications that make SAH an ICU disease rather than an ED one.

When SAH is missed and the patient subsequently rebleeds, the causation analysis turns on whether earlier diagnosis would have altered the trajectory. That is rarely a question of whether treatment existed — it almost always did. It is a question of whether this particular patient, with this aneurysm, at this point in time, would have been a candidate for securing, and whether securing would have prevented the subsequent rerupture or the downstream complication. Those are specific questions, answered against specific imaging, specific aneurysm morphology, and the specific interval between the missed presentation and the rerupture. General appeals to "earlier treatment would have helped" do not survive deposition on this disease; the analysis has to be the patient's, not the population's.

Reading the Record

A defensible SAH case — plaintiff or defense — rests on what the record documents and on what it omits. A careful review pins down:

• The history as documented at triage and at physician evaluation. Was the onset characterized (sudden vs. gradual, time to peak)? Was the comparison to prior headaches elicited? Was the sentinel headache history asked about? Or is the record's operative history simply "headache, four hours"?
• The timing of imaging relative to symptom onset, and the CT scanner generation and reader level. A negative CT at four hours on a modern scanner read by a neuroradiology attending is a different finding than a negative CT at eighteen hours on an older scanner read by a senior resident.
• The LP, if performed: the interval between symptom onset and LP; the presence or absence of xanthochromia analysis; the reasoning applied to any RBC findings. If LP was deferred in favor of CTA, the documentation for that decision.
• The return visit, when it occurred: what had changed, what precipitated re-presentation, what the imaging on return showed, and what the interval rebleed or clinical deterioration looks like on the second-look record.
• The aneurysm: its location, size, morphology, and whether it would have been a candidate for treatment at the time of the missed presentation. An aneurysm that could not have been secured safely in the window between the missed presentation and the rerupture cannot anchor a causation theory, even in an egregious miss.

Most missed SAH cases resolve once these elements are placed in order. A case that looked strong on the complaint sometimes dissolves against a sentinel headache history that was genuinely not elicitable because the patient could not provide one. A defense that looked strong sometimes collapses against a chart that documents a classic thunderclap history and a CT obtained at hour nineteen with no LP to follow. The analytical work is not inventing a narrative the record does not support. It is reading the record carefully and declining to supply what is not there.

References

Footnotes

1. Vermeulen MJ, Schull MJ. Missed diagnosis of subarachnoid hemorrhage in the emergency department. Stroke. 2007;38(4):1216–1221. doi:10.1161/01.STR.0000259661.05525.9a ↩ ↩²

2. Kowalski RG, Claassen J, Kreiter KT, et al. Initial misdiagnosis and outcome after subarachnoid hemorrhage. JAMA. 2004;291(7):866–869. doi:10.1001/jama.291.7.866 ↩ ↩²

3. Edlow JA, Caplan LR. Avoiding pitfalls in the diagnosis of subarachnoid hemorrhage. N Engl J Med. 2000;342(1):29–36. doi:10.1056/NEJM200001063420106 ↩

4. Perry JJ, Stiell IG, Sivilotti MLA, et al. Sensitivity of computed tomography performed within six hours of onset of headache for diagnosis of subarachnoid haemorrhage: prospective cohort study. BMJ. 2011;343:d4277. doi:10.1136/bmj.d4277 ↩

5. Dubosh NM, Bellolio MF, Rabinstein AA, Edlow JA. Sensitivity of Early Brain Computed Tomography to Exclude Aneurysmal Subarachnoid Hemorrhage: A Systematic Review and Meta-Analysis. Stroke. 2016;47(3):750–755. doi:10.1161/STROKEAHA.115.011386 ↩

6. Carpenter CR, Hussain AM, Ward MJ, et al. Spontaneous Subarachnoid Hemorrhage: A Systematic Review and Meta-analysis Describing the Diagnostic Accuracy of History, Physical Examination, Imaging, and Lumbar Puncture With an Exploration of Test Thresholds. Acad Emerg Med. 2016;23(9):963–1003. doi:10.1111/acem.12984 ↩ ↩²

7. Mark DG, Hung YY, Offerman SR, et al. Nontraumatic subarachnoid hemorrhage in the setting of negative cranial computed tomography results: external validation of a clinical and imaging prediction rule. Ann Emerg Med. 2013;62(1):1–10.e1. doi:10.1016/j.annemergmed.2012.09.003 ↩

8. Connolly ES Jr, Rabinstein AA, Carhuapoma JR, et al. Guidelines for the Management of Aneurysmal Subarachnoid Hemorrhage: A Guideline for Healthcare Professionals From the American Heart Association/American Stroke Association. Stroke. 2012;43(6):1711–1737. doi:10.1161/STR.0b013e3182587839 ↩