Acute headache is one of the most frequent presenting complaints in emergency and outpatient clinical practice. Although most headaches are attributable to primary headache disorders, acute headache can occasionally represent a serious secondary intracranial condition such as intracranial hemorrhage, ischemic stroke, intracranial mass lesion, hydrocephalus, cerebral infection, or venous thrombosis. Early recognition of these conditions is important because delayed diagnosis may result in significant morbidity and mortality.1,2 Neuroimaging is therefore frequently requested in patients with acute headache, particularly when clinical features raise suspicion for secondary pathology. Computed tomography (CT) of the brain remains an important first-line imaging modality in emergency settings because of its rapid acquisition, widespread availability, and high sensitivity for acute intracranial hemorrhage and several other important abnormalities. Current American College of Radiology criteria consider noncontrast CT of the head usually appropriate in patients with sudden severe headache and in patients with headache accompanied by red flags such as increasing severity, fever, neurological deficit, older age at onset, malignancy, immunocompromise, or trauma.3–5 However, the diagnostic yield of CT among patients presenting with headache varies considerably according to the population studied and the clinical characteristics prompting imaging. A multinational study of emergency department headache presentations reported an overall CT diagnostic yield of approximately 10%, with substantial variation between regions. A retrospective emergency-department study of 501 patients found that abnormal CT findings were associated with older age, very early presentation after headache onset, aphasia, and focal neurological deficits.4 Previous studies have also demonstrated that the presence of focal neurological deficits and increasing age are important predictors of clinically relevant abnormalities on head CT.6,7 A systematic review and meta-analysis found that clinically significant abnormalities on neuroimaging among patients with headache occurred in approximately 8.9% of patients overall, although prevalence varied according to headache characteristics and study population.8 Despite these data, the spectrum of CT findings among patients presenting with acute headache can vary according to patient demographics, referral patterns, and local disease burden. Characterizing the local spectrum of findings may help clinicians and radiologists understand the diagnostic yield of CT and identify clinical characteristics associated with significant abnormalities. The present study was therefore conducted to determine the spectrum of CT brain findings among adult patients presenting with acute headache and to evaluate the association between selected clinical characteristics and abnormal CT findings.

Study design and setting This was a retrospective observational study conducted in the Department of Radiology of a tertiary-care teaching hospital in Haryana, India. Patients who underwent CT brain examination for acute headache during a 12-month study period were evaluated. Study population comprised of all adult patients aged ≥18 years who presented with acute headache and underwent CT brain imaging were considered eligible. Inclusion criteria Patients were included if they: 1. Were aged ≥18 years. 2. Presented with acute headache. 3. Underwent CT brain examination as part of their clinical evaluation. 4. Had adequate clinical and radiological records available for analysis. Exclusion criteria Patients were excluded if they: 1. Had a history of recent major head trauma where trauma was the primary indication for CT. 2. Had previously diagnosed intracranial malignancy or established intracranial pathology for which CT was performed as follow-up rather than evaluation of headache. 3. Had incomplete clinical records. 4. Had technically inadequate CT examinations. Clinical data collection Data were retrieved from electronic medical records and radiology information systems from the medical records department. The variables recorded were age, gender, duration of headache, onset, severity, associated vomiting, fever, altered sensorium, focal neurological deficit, history of malignancy, immunocompromised state and presence of headache red flags which was considered when there was sudden/thunderclap onset, increasing severity or frequency, fever, neurological deficit, age >50 years at new headache onset, history of malignancy/immunocompromise, or other clinical concern for secondary headache. CT examination CT brain examinations were performed using a multidetector CT scanner Siemens Somatom Emotion according to institutional protocols. Noncontrast CT was performed as the initial examination in most patients. Contrast-enhanced CT or additional vascular imaging was performed when clinically indicated. CT images were interpreted by all qualified radiologists with similar experience for the purpose of this study. The following findings were specifically recorded: • Normal CT • Acute ischemic infarction • Intracerebral hemorrhage • Subarachnoid hemorrhage • Subdural hematoma • Epidural hematoma • Intracranial mass lesion • Hydrocephalus • Cerebral edema • Sinusitis • Chronic ischemic changes • Cerebral atrophy • Other abnormalities When multiple abnormalities were present, the clinically dominant finding was recorded as the primary CT diagnosis. Definition of abnormal CT For analysis, CT examinations were categorized into two categories. It was a normal CT if no intracranial abnormality relevant to the presenting headache while it was considered an abnormal CT if there was presence of an intracranial or extracranial abnormality detected on CT. For secondary analysis, acute clinically significant abnormalities included acute infarction, intracranial hemorrhage, mass lesion, hydrocephalus, cerebral edema, and other acute intracranial pathologies requiring clinical intervention or further evaluation. Statistical analysis Data were analyzed using statistical package for social science V26.0 software (IBM, USA). Continuous variables were expressed as mean ± standard deviation or median with interquartile range, as appropriate. Categorical variables were presented as frequencies and percentages. The association between categorical variables and CT abnormalities was assessed using the chi-square test or Fisher's exact test where appropriate. Odds ratios (ORs) with 95% confidence intervals (CIs) were calculated for selected clinical predictors. A two-sided p-value <0.05 was considered statistically significant

A total of 300 patients fulfilled the inclusion criteria. The mean age of the study population was 43.8 ± 19.1 years, with an age range of 18–87 years. Women constituted 54.7% of the study population, while men constituted 45.3%. The largest age group was 40–59 years, comprising 101 patients (33.7%). Table 1. Demographic characteristics of the study population Variable n (%) Total patients 300 (100) Age, mean ± SD (years) 43.8 ± 19.1 Age range (years) 18–87 Age group 18–19 years 30 (10.0) 20–39 years 94 (31.3) 40–59 years 101 (33.7) ≥60 years 75 (25.0) Sex Male 136 (45.3) Female 164 (54.7) Among the 300 patients evaluated for acute headache, nausea/vomiting was the most frequently documented associated symptom, occurring in 82 patients (27.3%). Focal neurological deficits were present in 72 patients (24.0%), while increasing headache severity or frequency was reported in 57 patients (19.0%). Sudden or thunderclap onset was documented in 48 patients (16.0%), and visual symptoms were reported in 39 patients (13.0%). Fever and altered sensorium were observed in 31 (10.3%) and 26 (8.7%) patients, respectively. A history of immunocompromise was present in 11 patients (3.7%), whereas 8 patients (2.7%) had a history of malignancy. Overall, 120 patients (40.0%) had at least one headache red flag. The relatively frequent occurrence of focal neurological deficits, sudden headache onset, and increasing headache severity is clinically relevant because these features may raise suspicion for secondary intracranial pathology and support the use of neuroimaging in appropriately selected patients. It should be noted that the clinical characteristics were not mutually exclusive, and several patients had more than one associated symptom or risk factor; therefore, the individual percentages cannot be summed to derive an overall percentage. Table 2. Clinical characteristics of patients presenting with acute headache Clinical characteristic n (%) Sudden/thunderclap onset 48 (16.0) Increasing severity/frequency 57 (19.0) Nausea/vomiting 82 (27.3) Fever 31 (10.3) Visual symptoms 39 (13.0) Altered sensorium 26 (8.7) Focal neurological deficit 72 (24.0) History of malignancy 8 (2.7) History of immunocompromise 11 (3.7) At least one red flag 120 (40.0) Note: Some patients had more than one clinical feature. Of the 300 patients who underwent CT brain examination for acute headache, 198 (66.0%) had a normal CT examination, whereas 102 (34.0%) demonstrated an abnormal CT finding. Among the abnormal examinations, acute ischemic infarction was the most frequently observed finding, identified in 25 patients (8.3% of the total study population). Intracerebral hemorrhage was observed in 20 patients (6.7%), followed by subdural hematoma in 12 patients (4.0%) and subarachnoid hemorrhage in 10 patients (3.3%). Intracranial mass lesions were identified in 9 patients (3.0%). Sinusitis was detected in 14 patients (4.7%) and represented the most frequent non-intracranial finding. Hydrocephalus and cerebral edema were observed in 5 (1.7%) and 4 (1.3%) patients, respectively, while other CT abnormalities were documented in 3 patients (1.0%). Overall, the majority of patients presenting with acute headache had no significant abnormality on CT brain examination. However, approximately one-third of patients demonstrated an identifiable abnormality, with acute ischemic infarction and intracranial hemorrhagic conditions constituting the predominant clinically important intracranial findings in this cohort. Table 3. Spectrum of CT brain findings among patients presenting with acute headache CT finding n (%) Normal CT brain 198 (66.0) Abnormal CT 102 (34.0) Abnormal CT Acute ischemic infarction 25 (8.3) Intracerebral hemorrhage 20 (6.7) Subdural hematoma 12 (4.0) Subarachnoid hemorrhage 10 (3.3) Intracranial mass lesion 9 (3.0) Sinusitis 14 (4.7) Hydrocephalus 5 (1.7) Cerebral edema 4 (1.3) Other findings 3 (1.0) Total 300 (100) Percentages for individual CT findings were calculated using the total study population (N=300). Individual abnormal CT categories are mutually exclusive and represent the predominant finding in each patient. The “Abnormal CT findings” row is a summary category and is not an additional finding. Among the 102 patients with abnormal CT examinations, 88 had clinically significant acute intracranial abnormalities, while 14 had isolated sinusitis or other non-acute/incidental findings. Table 4. Clinical categorization of CT findings CT category n (%) Normal CT 198 (66.0) Acute clinically significant intracranial pathology 88 (29.3) Non-acute/incidental or extracranial finding 14 (4.7) Total 300 (100) Thus, the overall prevalence of clinically significant acute intracranial pathology was 29.3% in this cohort. This proportion was higher than the diagnostic yields reported in several emergency department-based imaging studies, which may be attributable to the tertiary-care referral nature of the study center, where patients with more complex and clinically suspected intracranial conditions are more likely to be referred for imaging. A significant association was observed between age and CT brain findings. Among patients younger than 50 years, 38 of 160 (23.8%) demonstrated an abnormal CT finding, whereas 64 of 140 (45.7%) patients aged ≥50 years had an abnormal CT examination. Conversely, normal CT findings were more frequent among patients younger than 50 years than among those aged ≥50 years (76.3% vs. 54.3%). The difference in the distribution of normal and abnormal CT findings between the two age groups was statistically significant (χ² = 16.05, p <0.001). Patients aged ≥50 years had approximately 2.7-fold higher odds of demonstrating an abnormal CT finding compared with patients younger than 50 years (OR 2.70, 95% CI: 1.65–4.43). These findings indicate that increasing age was significantly associated with a higher likelihood of abnormal CT findings among patients presenting with acute headache. Table 5. Association between age and CT brain findings among patients presenting with acute headache Age group Normal CT, n (%) Abnormal CT, n (%) Total, n (%) χ² p-value OR (95% CI) <50 years 122 (76.3) 38 (23.8) 160 (53.3) 16.05 <0.001 Reference ≥50 years 76 (54.3) 64 (45.7) 140 (46.7) 2.70 (1.65–4.43) Total 198 (66.0) 102 (34.0) 300 (100) OR, odds ratio; CI, confidence interval. Note: Percentages in the Normal CT and Abnormal CT columns are calculated within each age group. Percentages in the Total column are calculated using the entire study population (N=300). Patients aged <50 years served as the reference category. A significant association was observed between the presence of a focal neurological deficit and abnormal CT brain findings. Among the 72 patients with a focal neurological deficit, 48 (66.7%) demonstrated an abnormal CT examination, whereas 24 (33.3%) had a normal CT. In comparison, among the 228 patients without a focal neurological deficit, 54 (23.7%) had an abnormal CT and 174 (76.3%) had a normal CT. The difference in the distribution of CT findings between patients with and without focal neurological deficits was statistically significant (Pearson's χ² = 45.05, df = 1, p <0.001). Patients presenting with a focal neurological deficit had significantly higher odds of an abnormal CT finding than those without a focal neurological deficit (OR 6.44, 95% CI: 3.62–11.48). Thus, the presence of a focal neurological deficit was strongly associated with abnormal neuroimaging findings in patients presenting with acute headache. Table 6. Association between focal neurological deficit and CT brain findings Focal neurological deficit Normal CT, n (%) Abnormal CT, n (%) Total, n (%) χ² p-value OR (95% CI) Present 24 (33.3) 48 (66.7) 72 (24.0) 45.05 <0.001 6.44 (3.62–11.48) Absent 174 (76.3) 54 (23.7) 228 (76.0) Reference Total 198 (66.0) 102 (34.0) 300 (100) Note: Percentages in the Normal CT and Abnormal CT columns are calculated within each neurological-deficit category. Total percentages are calculated using the entire study population (N=300). OR, odds ratio; CI, confidence interval. A significant association was observed between the presence of headache red flags and abnormal CT brain findings. Among the 120 patients with at least one headache red flag, 66 (55.0%) demonstrated an abnormal CT examination, while 54 (45.0%) had a normal CT. In comparison, among the 180 patients without a documented red flag, only 36 (20.0%) had an abnormal CT finding, whereas 144 (80.0%) had a normal CT examination. The difference between the two groups was statistically significant (Pearson's χ² = 39.30, df = 1, p <0.001). Patients with at least one headache red flag had approximately 4.9-fold higher odds of demonstrating an abnormal CT finding compared with patients without red flags (OR 4.89, 95% CI: 2.93–8.16). These findings indicate that the presence of headache red flags was significantly associated with a higher likelihood of abnormal neuroimaging findings in patients presenting with acute headache. Table 7. Association between headache red flags and CT brain findings Headache red flag Normal CT, n (%) Abnormal CT, n (%) Total, n (%) χ² p-value OR (95% CI) Present 54 (45.0) 66 (55.0) 120 (40.0) 39.30 <0.001 4.89 (2.93–8.16) Absent 144 (80.0) 36 (20.0) 180 (60.0) Reference Total 198 (66.0) 102 (34.0) 300 (100) Note: Percentages in the Normal CT and Abnormal CT columns are calculated within each red-flag category. Total percentages are calculated using the entire study population (N=300). OR, odds ratio; CI, confidence interval. The association between selected clinical predictors and abnormal CT findings is summarized in Table 8. All three evaluated predictors demonstrated a statistically significant association with abnormal CT findings. Patients aged ≥50 years had 2.70-fold higher odds of an abnormal CT finding compared with those younger than 50 years (OR 2.70, 95% CI: 1.65–4.43; p <0.001). The strongest association was observed for focal neurological deficits, with patients presenting with a focal neurological deficit having 6.44-fold higher odds of an abnormal CT finding compared with those without such deficits (OR 6.44, 95% CI: 3.62–11.48; p <0.001). Similarly, patients with at least one headache red flag had 4.89-fold higher odds of an abnormal CT finding compared with patients without red flags (OR 4.89, 95% CI: 2.93–8.16; p <0.001). Among the evaluated predictors, focal neurological deficit demonstrated the strongest association with abnormal CT findings. Table 8. Clinical predictors associated with abnormal CT findings Predictor Abnormal CT / Total, n (%) Odds ratio (OR) 95% CI p-value Age ≥50 years 64/140 (45.7) 2.70 1.65–4.43 <0.001 Focal neurological deficit 48/72 (66.7) 6.44 3.62–11.48 <0.001 ≥1 headache red flag 66/120 (55.0) 4.89 2.93–8.16 <0.001 Note: ORs represent the odds of an abnormal CT finding in patients with the specified predictor compared with those without the predictor. Reference categories were age <50 years, absence of focal neurological deficit, and absence of headache red flags, respectively. CI, confidence interval.

In this retrospective sample, approximately two-thirds of patients presenting with acute headache had a normal CT brain examination, whereas one-third demonstrated an abnormality. Acute ischemic infarction was the most frequent intracranial abnormality, followed by intracerebral hemorrhage, subdural hematoma, and subarachnoid hemorrhage. Older age, focal neurological deficit, and the presence of headache red flags were significantly associated with abnormal CT findings. The relatively high proportion of normal CT examinations is consistent with the observation that headache is frequently caused by primary headache disorders or other conditions without acute intracranial pathology. A systematic review and meta-analysis of neuroimaging in headache patients reported a pooled prevalence of clinically significant abnormalities of approximately 8.9%, although substantial variation existed between study populations.8 Similarly, an international study evaluating CT utilization in emergency department headache presentations reported an overall diagnostic yield of approximately 9.9%.9 The higher abnormality rate in the present cohort may be explained by the tertiary-care setting and selection of patients who underwent CT because of clinical concern for secondary headache. This distinction is important because the diagnostic yield of CT cannot be interpreted independently of the clinical threshold used for imaging. Age was significantly associated with abnormal CT findings. Patients aged ≥50 years had approximately 2.7-fold higher odds of an abnormal examination. This finding is consistent with previous literature. In a retrospective emergency-department study of patients presenting with headache, age ≥50 years was associated with abnormal cranial CT findings.4 Similarly, a large study of non-traumatic emergency head CT examinations demonstrated increasing age as an independent predictor of clinically important abnormalities.6 Focal neurological deficit demonstrated the strongest association with abnormal CT in our sample. Approximately two-thirds of patients with a focal neurological deficit had abnormal CT findings, compared with less than one-fourth of patients without a deficit. The odds of an abnormal CT were more than sixfold higher in patients with focal neurological deficits. This observation is in agreement with previous studies identifying focal neurological deficits as one of the strongest predictors of clinically important CT abnormalities.6,7 The association between headache red flags and abnormal imaging was also significant. Patients with at least one red flag had nearly five times the odds of an abnormal CT. Clinically important red flags include sudden severe headache, increasing headache frequency or severity, fever, neurological deficit, older age at onset, malignancy, immunocompromise, and post-traumatic headache. The ACR Appropriateness Criteria specifically identify these features as scenarios in which neuroimaging may be appropriate.10,11 Intracranial hemorrhage represented an important component of the CT spectrum in our study. This is clinically relevant because noncontrast CT is particularly valuable for rapid assessment of acute hemorrhage. In patients presenting with thunderclap headache, the timing of CT is also important. Evidence synthesized in a systematic review indicates that CT performed within six hours of headache onset has very high diagnostic accuracy for subarachnoid hemorrhage in appropriately selected patients, whereas sensitivity decreases when imaging is performed later.12,13 The identification of acute ischemic infarction as the most common major abnormality in this sample also emphasizes that headache can occasionally accompany cerebrovascular disease. However, noncontrast CT has limited sensitivity for early ischemic changes compared with MRI. Therefore, a normal initial CT should not necessarily be interpreted as excluding ischemia when clinical suspicion remains high. Sinusitis represented the most frequent non-intracranial or incidental finding in the sample. The clinical significance of such findings should be interpreted cautiously because abnormalities detected on CT may not necessarily explain the patient's headache. Radiologists should therefore distinguish clinically meaningful intracranial pathology from incidental or nonspecific findings. The results also support the concept that CT utilization should be guided by clinical risk assessment rather than headache alone. Previous research has demonstrated that indiscriminate imaging can result in a low diagnostic yield, while the presence of selected clinical characteristics can substantially increase the likelihood of clinically relevant abnormalities.7,14 For patients with sudden severe headache, clinical assessment remains essential. CT is commonly used as an initial investigation, particularly when subarachnoid hemorrhage or other acute intracranial pathology is suspected. The appropriate subsequent investigation depends on the timing of presentation, CT findings, neurological examination, and the specific suspected diagnosis. An important implication of this study is that radiology and clinical assessment should be viewed as complementary rather than competing approaches. The radiologist should receive sufficient clinical information regarding headache onset, duration, associated neurological symptoms, and relevant risk factors. Better clinical-radiological communication may improve interpretation and appropriate escalation to additional imaging such as CT angiography, CT venography, or MRI when indicated. The study has several limitations. First, its retrospective design limits the ability to establish causal relationships between clinical features and CT findings. Second, the study was conducted at a single tertiary-care center, limiting generalizability. Third, the decision to perform CT was made by treating clinicians and was not standardized. This introduces selection bias because patients with greater clinical concern for secondary headache were more likely to undergo imaging. Fourth, CT alone may underestimate certain pathologies, particularly early ischemia, small posterior fossa lesions, and some venous or inflammatory conditions that may be better evaluated with MRI or dedicated vascular imaging.

CT brain examination in patients presenting with acute headache demonstrated a broad spectrum of findings, ranging from completely normal examinations to potentially life-threatening intracranial pathology. In this cohort, acute ischemic infarction and intracranial hemorrhage were the most important pathological findings. Older age, focal neurological deficit, and the presence of headache red flags were significantly associated with abnormal CT findings. These findings highlight the importance of appropriate clinical risk stratification when deciding which patients presenting with acute headache are most likely to benefit from neuroimaging. CT remains an important first-line investigation in selected patients with acute headache, particularly when secondary causes are suspected. However, a normal CT should be interpreted in the context of the clinical presentation and should not preclude additional imaging when clinical suspicion remains high. Ethics approval The study was reviewed and approved by the Institutional Ethics Committee. As this was a retrospective study involving routinely collected clinical data and no direct patient intervention, the requirement for individual informed consent was waived by the Ethics Committee.

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