Is cerebral perfusion analysis using computed tomography (CT) with contrast administration, CPT code 0042T, medically indicated for a patient with suspected acute stroke and postsurgical changes related to left temporal tumor resection?

Medical Necessity Determination for CPT 0042T - Cerebral Perfusion CT Analysis

Direct Recommendation

CT perfusion analysis (CPT 0042T) was medically indicated for this patient presenting with suspected acute stroke within the first 24 hours, as the clinical presentation of acute neurological deficit with suspected stroke meets established criteria for cerebral perfusion imaging, regardless of the incidental finding of postsurgical changes from prior tumor resection. 1

Rationale Based on Clinical Presentation

Primary Indication Met: Acute Stroke Evaluation

• The patient presented with acute neurological symptoms (R29.818 - other symptoms and signs involving the nervous system) with clinical suspicion of acute stroke, which is the primary indication for CT perfusion studies 1

• The ACR Appropriateness Criteria (2017) assigns CT head perfusion a rating of 6 ("may be appropriate") for new focal neurologic deficits within 6 hours and a rating of 5 ("may be appropriate") for deficits beyond 6 hours, indicating this is a recognized diagnostic modality in the acute stroke setting 1

• The Aetna criteria explicitly state that cerebral CT perfusion studies are medically necessary for "diagnosis of acute ischemic stroke (within the first 24 hours), hemorrhagic stroke, subdural hemorrhage, and transient ischemic attacks" - this criterion was met 1

Technical and Clinical Utility

• CT perfusion provides quantitative assessment of cerebral blood flow (CBF), cerebral blood volume (CBV), and mean transit time (MTT), which are critical parameters for identifying salvageable brain tissue (penumbra) versus irreversibly damaged core in acute stroke 1

• The technique has been validated as a reliable alternative to MR perfusion in acute ischemia, with the ability to assess collateral flow patterns that predict prognosis 1

• Dynamic CT perfusion can detect perfusion abnormalities even when standard noncontrast CT shows no acute changes, which is particularly relevant given this patient's CT showed "no imaging evidence of acute intracranial abnormality" on standard sequences 1

Addressing the Postsurgical Context

Why Prior Surgery Does Not Contraindicate the Study

• The postsurgical changes from left temporal tumor resection are incidental findings that do not negate the medical necessity of perfusion imaging for acute stroke evaluation 1

• While the surgical bed may show enhancement and altered perfusion patterns, CT perfusion analysis can still assess the remainder of the brain parenchyma for acute ischemic changes 2, 3

• The ACR guidelines do not list prior craniotomy or tumor resection as contraindications to CT perfusion imaging in the acute stroke setting 1

Critical Caveat for Interpretation

• Radiologists interpreting the perfusion study must be aware of the postsurgical changes, as the surgical bed may demonstrate abnormal perfusion parameters (altered CBV, CBF, and MTT) that should not be mistaken for acute ischemia 2, 3

• The presence of postsurgical granulation tissue with enhancement requires careful correlation with the noncontrast CT and CTA findings to distinguish chronic postsurgical changes from acute stroke 1

Clinical Decision Algorithm

When CT Perfusion is Indicated in Acute Stroke:

1. Patient presents with acute neurological deficit suspicious for stroke (✓ Met in this case) 1

2. Presentation is within 24 hours of symptom onset (✓ Appears met based on "acute stroke suspected") 1

3. Noncontrast CT has been performed to exclude hemorrhage (✓ Met - CTA brain and neck completed) 1

4. The study can be obtained expeditiously without delaying potential thrombolytic therapy (✓ Performed as part of comprehensive stroke protocol) 1

Specific Value in This Case:

• Standard CT and CTA showed no acute abnormality, but clinical suspicion remained high - this is precisely the scenario where perfusion imaging adds diagnostic value by detecting subtle perfusion deficits not visible on conventional imaging 1, 2

• The ability to quantify CBF, CBV, and MTT allows identification of tissue at risk that may benefit from intervention, even when structural imaging appears normal 1, 2

Common Pitfalls Avoided

Pitfall 1: Assuming Prior Surgery Precludes Perfusion Imaging

• This is incorrect - prior craniotomy does not contraindicate CT perfusion for acute stroke evaluation; it simply requires informed interpretation 1, 2

Pitfall 2: Relying Solely on Noncontrast CT

• Standard CT has only 61-65% sensitivity for detecting acute stroke within 6 hours, and perfusion imaging significantly improves detection of early ischemic changes 4

• The absence of acute findings on standard CT does not exclude acute stroke - perfusion imaging is specifically designed to detect functional deficits before structural changes become apparent 1, 2, 3

Pitfall 3: Delaying Perfusion Imaging Due to Uncertainty

• When acute stroke is suspected clinically, perfusion imaging should be obtained as part of the initial comprehensive stroke protocol, not deferred pending clinical evolution 1

Documentation Supporting Medical Necessity

The case documentation clearly establishes:

• Acute neurological presentation warranting stroke evaluation 1
• Clinical suspicion of acute stroke despite negative standard imaging 1, 2
• Appropriate timing within the acute stroke window 1
• Integration into comprehensive stroke imaging protocol (CTA already performed) 1

Therefore, CPT 0042T was medically indicated and appropriately utilized in this clinical scenario.