A Review of the Clinical Significance of Lumbar Puncture in the Diagnostic Approach of Aneurysmal Subarachnoid Hemorrhage (SAH): A Case Report of CT-Negative and Lumbar Puncture–Positive SAH


Subarachnoid hemorrhage (SAH) constitutes about 5% of strokes and 1%-3% of all headaches. [1,2]


SAH may be uncommon, but it is a life-threatening condition, with mortality rates approaching 50%. It also carries significant risks of serious morbidity, [3-5] which is why prompt and more importantly accurate diagnosis is paramount. Historically, a LP has been used to rule out SAH after a negative CT result. But in more recent years, with the advent of modern CT scans and CT angiography, [6,7] the role of LP as a means to rule out SAH has been questioned.

Other factors that disfavor LP are the risks associated with LP, including postdural puncture headache (PDPH), iatrogenic infections and brainstem herniation. The procedure is also painful and anxiety-provoking for most patients, further shadowing its benefits. [8,9] Because of this, other diagnostic approaches have been suggested as alternatives to LP, such as CT angiography (CTA) or magnetic resonance angiography (MRA). [8,10,11] Despite that, LP is still recommended by the AHA/ASA 2023 Guidelines for the Management of Aneurysmal Subarachnoid Hemorrhage for CT negative patients presenting after 6 hours. [12] Spinal fluid investigation may also help point to an alternative diagnosis in patients with atypical presentations.


Along with this case of CT-negative and LP-positive SAH, we aim to review the clinical significance of LP in the diagnostic approach of aneurysmal SAH, considering its risks and benefits to each patient and different individual circumstances.


Case Report

A 50-year-old female patient was admitted to the hospital with severe throbbing headache which had started three days prior to admission. The headache became severe enough that it interfered with her daily activities and sleep, and was no longer relieved with over-the-counter nonsteroidal anti-inflammatory drugs (NSAIDs). The patient denied any trauma, fever, neck stiffness, nausea or vomiting. She had no significant past medical or family history. She denied taking illicit drugs, smoking or drinking alcohol.


Motor strength and sensory exam were normal for both upper and lower limbs, and no cranial nerve or cerebellar deficits noted. There was no nuchal rigidity.


A cranial CT scan on admission showed no intracranial aneurysms or subarachnoid hemorrhage (SAH).


During the course of the hospital stay, the patient received tricyclic antidepressant, NSAID, muscle relaxants and benzodiazepines. However, her headache worsened, as observed on the pain scale. She also developed nuchal rigidity and light-headedness. Because of her deteriorating condition, the patient was taken for cranial magnetic resonance imaging and magnetic resonance angiography (MRI-MRA).


The MRI/MRA showed mild lateral bilateral ventriculomegaly with hyperintense debris and mild ependymal-leptomeningeal, as well as an arachnoid cyst in the left medial fossa (± 1.8 x 3.1 x 1.8 cm). A suspected saccular aneurysm was seen at the base of A2 (± 4 x 5 x 4 mm) with its dome facing anteriorly.


A LP was then performed, which showed xanthochromic fluid, 730/uL cells, positive Nonne Pandy test, 43 mg/dL glucose, 137 mg/dL protein and 107 mmol/L chloride.


A CT angiography (CTA) was done which showed mild subarachnoid hemorrhage in the chiasmatic cistern and posterior gray column of left lateral ventricle suspected coming from wide neck aneurysm in the segment border of A1-A2 right anterior cerebral artery with two small lumps facing the inferior wall of the aneurysm.


Digital subtraction angiography (DSA) showed a wide neck right anterior cerebral artery aneurysm and coiling of the aneurysm was performed. The headache receded several days after coiling and there were no further episodes of SAH.