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Neuroradiology Case of the Week

Case 111

Sarah Goldfeder and Per-Lennart Westesson, MD, PhD, DDS

Clinical Presentation:The patient is a 61-year-old female with a past medical history significant for diabetes mellitus, chronic renal failure, coronary artery disease status post myocardial infarction and PTCA, stroke, hypertension, hyperlipidemia, hypothyroidism, congestive heart failure, who presents with an acute swelling of the right side of her face and jaw in the setting of known staphylococcus bacteremia.

Radiological Findings: Contrast-enhanced CT reveals an enlarged and heterogeneous right parotid gland (arrow) with streaky opacities in overlying fat.  There is no ring enhancement.  There is no significant lymphadenopathy.

Diagnosis: Acute suppurative parotitis of the right parotid gland

Discussion: Acute suppurative parotitis (ASP) is a bacterial infection of the parotid gland that occurs when decreased salivary flow allows for retrograde ascension of bacteria from Stenson’s duct into the gland parenchyma. ASP is distinguished from viral parotitis, most commonly caused by the mumps virus, and chronic parotitis, which may be due to infectious, neoplastic, autoimmune, or systemic processes.
     Bacterial infection occurs more often in the parotid gland than in the submandibular gland for the following reasons. Parotid secretions are serous and thus less bacteriostatic than the mucinous secretions of the submandibular gland. Additionally, the opening of Stenson’s duct of the parotid gland is larger and more prone to injury than the opening of Wharton’s duct of the submandibular gland.
     Most cases of ASP occur in the elderly, although neonatal and premature infants are also at risk. Traditionally, ASP was seen following abdominal surgery. However, contemporary use of antibiotics has decreased its incidence to 0.01% to 0.02% of all hospital admissions and 0.002% to 0.04% of postoperative patients. Factors that increase the risk of developing ASP include post-operative dehydration, debilitating conditions, and immunosuppressive states. Examples of such conditions include diabetes mellitus, alcoholism, malnutrition, poor oral hygiene, HIV infection, Sjogren’s syndrome, renal and hepatic failure, hyperlipoproteinemia, and cystic fibrosis. Medications that can cause dehydration, such as antidepressants, anticholinergics, and diuretics, as well as ductal obstructions from sialolithiasis, tumor, or foreign bodies may also lead to ASP.
     Signs and symptoms of ASP include an erythematous, swollen, indurated, cheek, fever, pain, and expression of purulent discharge from Stenson’s duct. Staphylococcus aureus is the causal organism in more than 80% of all cases of ASP. Streptococcus viridans, Streptococcus pneumonia, Haemophilus influenzae, Streptococcus pyogenes, and Escherichia coli may also be the cause of the infection. The incidence of infection from strict anaerobes, such as Peptostreptococcus and Bacteriodes, is rising.
     CT scan is the imaging modality of choice for diagnosing ASP. CT without contrast will show an enlarged gland with increased attenuation due to cellular infiltration. With contrast, there may be diffuse enhancement due to increased vascularity. If a calcified stone is the cause of the parotitis, CT will reveal sialolithiasis. On MR, the gland is enlarged with obscuration of the normal architecture. T2-weighted imaging will show increased signal if there is mostly edema, but decreased signal if there is more cellular infiltration. Sialography is contraindicated in acute disease because the contrast can cause rupture of the duct as well as exacerbate the infection by pushing bacteria back into the gland.
     The first step in treating ASP is to rehydrate the patient to increase salivary flow and to initiate antibiotic therapy.  If medical therapy fails, if an abscess has developed, or if there is facial nerve involvement, then surgical incision and drainage via a parotidectomy is indicated. Finally, it is important to provide teaching on good oral hygiene to prevent further infection.

References:

1. Som and Curtin: Head and Neck Imaging, 4th ed., Volume One. 2003 Mosby: 2026-2029.
2. Fattahi TT, Lyu PE, Van Sickels JE. Management of acute suppurative parotitis. Journal of Oral and Maxillofacial Surgery. 2002. 60: 446-448. [Medline]
3. Cohen and Powderly: Infectious Diseases, 2nd ed., 2004 Elsevier: 464-466.