Pediatric Imaging

What Imaging Is Best for a Child with Suspected Invasive Fungal Sinusitis?

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What Imaging Is Best for a Child with Suspected Invasive Fungal Sinusitis?

An 11-year-old girl with acute myeloid leukemia, profoundly neutropenic following her latest round of induction chemotherapy, develops a persistent fever, right-sided facial pain, and a new, dark lesion on her hard palate. You are consulted in the pediatric intensive care unit, and your primary concern is a rapidly progressive, life-threatening infection. The clinical suspicion for invasive fungal sinusitis is high, and the next decision is critical: which imaging study will most accurately and quickly confirm the diagnosis and define the extent of disease to guide emergent surgical and medical therapy? This article details the clinical workflow for this specific, high-stakes scenario. According to the American College of Radiology (ACR) Appropriateness Criteria, an MRI of the paranasal sinuses without and with IV contrast is a Usually Appropriate initial study.

Who Fits the Clinical Scenario of Suspected Invasive Fungal Sinusitis?

This guidance applies specifically to pediatric patients where there is a strong clinical suspicion for invasive fungal sinusitis (IFS). This is not a diagnosis of exclusion; it is a primary consideration in a specific patient population.

Inclusion criteria for this scenario typically involve:

  • A severely immunocompromised state. This is the most critical predisposing factor. Common examples include profound neutropenia from chemotherapy (e.g., for leukemia or lymphoma), status post hematopoietic stem cell or solid organ transplant, chronic granulomatous disease, or advanced HIV infection. Children with poorly controlled diabetes mellitus, particularly with diabetic ketoacidosis, are also at high risk.
  • Suggestive clinical signs and symptoms. These often include fever unresponsive to broad-spectrum antibiotics, headache, facial pain or swelling (cellulitis), and nasal congestion or discharge. The pathognomonic but not universally present finding is a black, necrotic eschar on the nasal turbinates, septum, or palate.

This workflow is NOT for:

  • An immunocompetent child with uncomplicated sinusitis. A healthy child with typical cold symptoms, facial pressure, and purulent nasal discharge falls under the uncomplicated acute sinusitis scenario, where imaging is generally not indicated.
  • A child with persistent or recurrent sinusitis. A patient whose symptoms fail to improve after a standard course of antibiotics or who has multiple episodes of sinusitis per year fits a different clinical variant requiring a distinct workup.
  • A child with clear orbital or intracranial complications without specific suspicion for fungal etiology. While there is overlap, the scenario of sinusitis with orbital or intracranial complications is broader. This article focuses on the specific need to identify angioinvasion and tissue necrosis characteristic of fungal disease.

What Diagnoses Are You Working Up with This Imaging?

When ordering imaging for suspected IFS, you are evaluating a narrow but critical differential for destructive sinonasal disease in a vulnerable patient. The primary goal is to confirm invasion and delineate its extent to guide immediate, aggressive treatment.

Invasive Fungal Sinusitis (IFS)
This is the leading concern and a true medical emergency. Caused by angioinvasive fungi like Aspergillus and Mucorales species, the infection spreads rapidly from the sinus mucosa to invade blood vessels, causing thrombosis, tissue infarction, and necrosis. From there, it can extend directly into the orbits, cavernous sinuses, and brain. Imaging is crucial for detecting the hallmark signs of non-enhancing, devitalized tissue and defining the full extent of spread, which is often far greater than what is visible on physical exam.

Complicated Acute Bacterial Sinusitis
While less common in this specific patient population, a severe, aggressive bacterial infection can also lead to extensive inflammation, bone erosion, and abscess formation (e.g., orbital or epidural abscess). Imaging helps differentiate this from IFS by evaluating tissue enhancement patterns. In bacterial infection, inflamed tissues and abscess walls typically demonstrate avid enhancement, in contrast to the non-enhancement seen with fungal-induced necrosis.

Sinonasal Malignancy
Although rare in children, certain aggressive cancers like rhabdomyosarcoma, lymphoma, or Ewing sarcoma can arise in the sinonasal cavity. In an immunocompromised child, a new or rapidly growing malignancy can mimic infection. Imaging features such as a discrete, enhancing soft tissue mass with bone destruction can suggest malignancy, prompting a biopsy for definitive diagnosis.

Why Is MRI with Contrast the Recommended Initial Study for Suspected Invasive Fungal Sinusitis?

The choice of imaging in suspected invasive fungal sinusitis is driven by the need to visualize soft tissue invasion and vascular compromise with high fidelity. The ACR rates both MRI of the paranasal sinuses without and with IV contrast and CT of the paranasal sinuses with IV contrast as Usually Appropriate. While both are valid first-line options, MRI is often favored for its superior soft tissue resolution.

The primary strength of MRI is its unparalleled ability to characterize soft tissue. It can detect subtle signs of early perineural, orbital, and intracranial spread that may be occult on CT. The administration of intravenous contrast is non-negotiable and is the most critical component of the study. The hallmark of angioinvasive fungal disease is vascular occlusion leading to tissue infarction. On post-contrast MRI, this devitalized, necrotic tissue will appear as areas of non-enhancement surrounded by inflamed, enhancing mucosa. This finding is highly specific for IFS and is the key feature that guides emergent surgical debridement.

Comparing Appropriate and Inappropriate Alternatives:

  • CT paranasal sinuses with IV contrast is also rated Usually Appropriate. It is significantly faster than MRI—a major advantage in an unstable patient—and provides superior visualization of bony erosion. It can also demonstrate soft tissue non-enhancement. The choice between MRI and CT often comes down to patient stability, scanner availability, and institutional preference. However, for assessing early intracranial or cavernous sinus involvement, MRI remains the superior modality.
  • CT paranasal sinuses without IV contrast is rated Usually Not Appropriate. Without contrast, it is impossible to assess for the critical finding of mucosal non-enhancement. While it can show bone destruction and sinus opacification, it cannot reliably differentiate invasive fungal disease from severe bacterial sinusitis or other inflammatory conditions, making it an inadequate study for this specific question.
  • MRI paranasal sinuses without IV contrast is also Usually Not Appropriate. Similar to non-contrast CT, an unenhanced MRI cannot demonstrate the lack of perfusion in necrotic tissue. The key diagnostic information is derived from the post-contrast sequences. Ordering this study without contrast misses the primary pathologic correlate of the disease.

For this pediatric population, MRI offers the significant benefit of avoiding ionizing radiation (0 mSv). While the dose from a pediatric head/sinus CT is managed carefully, eliminating it entirely is always preferable when a non-radiation alternative provides equivalent or superior diagnostic information.

What’s Next After MRI? Downstream Clinical Workflow

The imaging results in a case of suspected invasive fungal sinusitis directly trigger an urgent, multidisciplinary response. The radiologist’s interpretation is not the end of the workup but the beginning of an aggressive treatment pathway.

  • If the MRI is positive for IFS: A finding of non-enhancing sinus mucosa, particularly with evidence of extension into adjacent structures (orbit, brain, cavernous sinus), is a surgical emergency. The immediate next steps are:

1. Urgent surgical consultation: An otolaryngologist (ENT) and potentially a neurosurgeon or ophthalmologist should be consulted immediately for emergent, wide surgical debridement of all necrotic tissue.
2. Initiate or broaden systemic antifungal therapy: High-dose, broad-spectrum antifungal agents (e.g., liposomal amphotericin B) should be started empirically if not already underway.
3. Obtain tissue for pathology and culture: Surgical specimens are critical for definitive histopathologic confirmation of fungal hyphae invading tissue and for culture to identify the specific organism and guide targeted therapy.

  • If the MRI is negative for IFS: If the study shows only simple mucosal thickening and enhancement without signs of invasion or necrosis, the diagnosis of IFS is unlikely. The focus should shift to other causes. This may involve:

1. Re-evaluating for an aggressive bacterial source and optimizing antibiotic therapy.
2. Considering a biopsy if a discrete mass or atypical inflammation is seen, to rule out malignancy.
3. Continuing close clinical monitoring, as early IFS can sometimes have subtle imaging findings.

  • If the MRI is indeterminate: In cases with ambiguous findings, such as diffuse, intense inflammation without clear non-enhancement, the next step is often direct endoscopic evaluation and biopsy by ENT. A tissue sample remains the gold standard for diagnosis.

Pitfalls to Avoid (and When to Get Help)

In this time-sensitive clinical scenario, missteps in the diagnostic process can have devastating consequences. Be aware of these common pitfalls:

  • Delaying imaging: Clinical suspicion of IFS warrants emergent imaging. Do not wait for classic signs like black eschar to appear, as the disease may have already progressed significantly.
  • Ordering a non-contrast study: The most critical diagnostic information comes from the post-contrast sequences. Ordering a CT or MRI without IV contrast is a major diagnostic error in this context.
  • Misinterpreting sinus opacification: On non-contrast imaging, both simple fluid/inflammation and necrotic tissue can appear as sinus opacification. Only a contrast-enhanced study can differentiate them reliably.
  • Underestimating the need for sedation: Young or clinically unstable children will likely require sedation or general anesthesia to obtain a high-quality, motion-free MRI. Plan for this in advance with anesthesiology to avoid delays.

If you see imaging findings suggestive of vascular invasion, cavernous sinus thrombosis, or intracranial extension, escalate immediately to your ENT, neurosurgery, and infectious disease colleagues. This is a multidisciplinary emergency.

Related ACR Topics and Tools

For a comprehensive overview of imaging for all pediatric sinusitis scenarios, from uncomplicated to recurrent, please see our parent topic hub article. For tools to help you select the right study and understand the technical details, the resources below are available.

Frequently Asked Questions

Why is MRI preferred over CT if both are rated ‘Usually Appropriate’ for suspected invasive fungal sinusitis?

While both are excellent and appropriate first-line studies, MRI is often favored for its superior soft-tissue contrast, which allows for better detection of early invasion into the orbit, cavernous sinus, or brain parenchyma. It also avoids ionizing radiation. CT’s main advantages are its speed, which is beneficial for unstable patients, and its superior ability to detail bony erosion.

Is a non-contrast head CT sufficient if I’m worried about intracranial extension?

No. A non-contrast head CT is rated ‘Usually Not Appropriate’ for this indication. While it can show large-scale complications like a brain abscess or hemorrhage, it cannot assess for the key finding of non-enhancing, necrotic tissue within the sinuses, nor can it detect early dural or vascular invasion. A contrast-enhanced study (either CT or MRI) is mandatory.

What if my patient has renal insufficiency and I’m concerned about gadolinium contrast for an MRI?

This is a critical risk-benefit discussion. In a life-threatening condition like suspected invasive fungal sinusitis, the diagnostic benefit of a contrast-enhanced MRI almost always outweighs the risk of nephrogenic systemic fibrosis (NSF), especially with modern macrocyclic gadolinium-based contrast agents which carry a much lower risk. A contrast-enhanced CT is also an excellent alternative in this situation. Consult with your radiologist and nephrologist to make the best decision for the patient.

Can I order a CTA or MRA to look for vascular invasion?

CTA and MRA are rated ‘May be appropriate’ but are not the primary recommended initial studies. The standard post-contrast MRI or CT sequences are typically sufficient to infer vascular invasion by demonstrating non-enhancing tissue. A dedicated angiographic study may be considered as a problem-solving tool or for pre-operative planning if major vessel involvement (e.g., internal carotid artery) is suspected, but it should not replace the initial sinus-focused protocol.

The patient has a black eschar on their palate. Do I still need imaging before taking them to the OR?

Yes. Even with a pathognomonic clinical finding, imaging is essential before surgery. The physical exam cannot determine the full extent of the disease. Pre-operative imaging acts as a roadmap for the surgeon, showing how far the infection has spread into the orbits, cranial fossa, and other deep structures. This information is critical for planning the extent of the surgical debridement.

Reviewed by Pouyan Golshani, MD, Interventional Radiologist — May 29, 2026