Continuing Education Activity

Mesenteric adenitis is a syndrome characterized by right lower quadrant pain secondary to an inflammatory condition of mesenteric lymph nodes. This condition is classically mistaken for acute appendicitis due to their similarity in presentation. This activity describes the evaluation and management of mesenteric adenitis, and highlights the role of the physician in diagnosing and managing patients with this condition.

Objectives:

• Describe the etiology of mesenteric adenitis.
• Understand the key diagnostic criteria to correctly diagnose mesenteric adenitis.
• Describe the correct management of a patient diagnosed with mesenteric adenitis.
• Describe the clinical presentation of a patient with mesenteric adenitis.

Introduction

Mesenteric adenitis is a syndrome characterized by right lower quadrant pain secondary to an inflammatory condition of mesenteric lymph nodes. Lymph nodes are collections of tissue found throughout the body that are responsible for filtering bacteria, viruses, and waste products of the bloodstream. The clinical presentation of sudden onset right lower quadrant abdominal pain is similar to that of appendicitis and has classically been mistaken for it. This article will delineate the key differences between these two syndromes and provide a detailed discussion on the syndrome of mesenteric adenitis.

Etiology

The etiologies of mesenteric adenitis include several causes of inflammatory response within mesenteric lymph nodes. These include viral infections, bacterial infections, inflammatory bowel disease, or lymphoma. Two common gram-negative bacteria that are known to cause mesenteric adenitis include Yersinia pseudotuberculosis and Yersinia enterocolitica.[1] 

Other known culprits include salmonella, E coli, and streptococci. The etiology can further classify as primary versus secondary. Primary etiology occurs when the lymphadenopathy is the result of an unidentifiable inflammatory process. Secondary mesenteric adenitis occurs secondary to an intra-abdominal inflammatory process with a known source or etiology.

Epidemiology

The prevalence of mesenteric adenitis is largely unknown due to its self-resolving nature and rarity. However, there is a case series study in which 70 children were diagnosed with acute appendicitis clinically, but 16% of these had a final diagnosis of mesenteric adenitis later via surgery, imaging, or clinical course.[2]

Pathophysiology

Primary mesenteric adenitis is most commonly lymphadenopathy in the mesentery near the terminal ileum without a discoverable underlying cause for the inflammation.[1]  Mesenteric adenitis also presents secondary to bacterial or viral gastroenteritis. The pathophysiology for such infection to occur takes place as follows:  The bacteria/virus is ingested orally and able to enter the body's bloodstream via invasion through the intestinal epithelium.  The organism then localizes to the nodal lymph tissue of the body surrounding intestinal mucosa; this commonly occurs in Peyer's patches.  From there, the organism can spread regionally through lymphatic pathways to mesenteric lymph nodes resulting in mesenteric adenitis.

Histopathology

The lymphoid tissue of mesenteric adenitis, when examined under a microscope, will show an increased density of plasma cells and immunoblasts in the cortical and paracortical regions, capsular edema, and thickening, lymphocyte accumulation within dilated sinuses, and hyperplasia of germinal centers.[1]

History and Physical

Mesenteric adenitis most commonly presents in pediatric and young adult populations. A child under ten years of age who presents with acute onset right lower quadrant abdominal pain is more likely to have mesenteric adenitis rather than acute appendicitis. Mesenteric adenitis commonly follows recent gastroenteritis or upper respiratory infection. Common symptoms include fever, vomiting, change in bowel habits, periumbilical, and/or right lower quadrant abdominal pain. Many surgeons will note that pain from palpation during a physical exam is notably less in the presentation of mesenteric adenitis when compared to acute appendicitis.[3][4][5]

Evaluation

Labs

The clinician should obtain a complete blood count, C-reactive protein (CRP), and urine analysis. The WBC and CRP will generally be elevated, but the diagnosis cannot be ruled out even if they are within normal limits. The urinalysis is helpful to rule out a urinary tract infection. However, these laboratory studies will not help the clinician delineate between diagnoses of appendicitis, intussusception, or mesenteric adenitis.

Imaging

Abdominal ultrasonography is the gold standard for the diagnosis of mesenteric adenitis. Ultrasound that shows enlarged, hypoechoic mesenteric lymph nodes and the absence of a thickened blind-ending tubular structure (inflamed appendix) is diagnostic of mesenteric adenitis. The current radiological definition defines mesenteric adenitis as at least one abnormally enlarged lymph node measuring 8 mm or more in its short-axis diameter.[6][7] 

Lymph node enlargement can also present in acute appendicitis and perforated appendicitis, adding to the difficulty of correctly diagnosing the disease process; however, the lymph nodes tend to be less enlarged and numerous in cases of appendicitis. Recently, the use of superb microvascular imaging Doppler ultrasound has been studied in the pediatric population for achieving a diagnosis of mesenteric lymphadenitis.  This new technique of Doppler ultrasound has proven to show low-velocity blood flow with better image resolution when compared to color Doppler flow imaging.[8][9] 

A recent retrospective study compared the use of superb microvascular imaging (SMI) in addition to ultrasound with ultrasound alone in the pediatric patient population diagnosed with mesenteric lymphadenitis. The authors demonstrated increased sensitivity, specificity, and accuracy with the addition of SMI to ultrasound compared to ultrasound alone, 81.5% v. 63%, 76.7% v. 66.7%, and 78.9% v. 64.9%, respectively.[10]

Treatment / Management

A diagnosis of mesenteric adenitis is self-limiting and requires no treatment. Hence, the first step in management is to rule out the diagnoses, which require surgical intervention. After establishing the diagnosis of mesenteric adenitis, the treatment is as follows: supportive care with IV hydration and pain control with nonsteroidal anti-inflammatory medications. 

It is essential to explain the diagnosis clearly to the patient and family, as there is often no apparent cause; this can cause anxiety and concerns for patients and their families, so it is vital to warn them that improvement may take time and can happen slowly over several weeks.  It is appropriate to schedule office visits during this window to monitor their progress and discuss concerns.

Differential Diagnosis

The differential diagnosis includes appendicitis, intussusception, ovarian cyst rupture, ovarian abscess, ectopic pregnancy, endometriosis, ovarian torsion, testicular torsion, epididymitis, pelvic inflammatory disease, mesenteric ischemia, chronic abdominal pain, inflammatory bowel diseases such as Crohn's or ulcerative colitis, systemic lupus erythematous, malignancy, HIV, zoonotic infections, infectious mononucleosis, and tuberculosis.

Prognosis

The pain typically resolves within four weeks without sequelae.  Again, patients/families should be instructed about the length of this recovery and may be followed in the clinic to monitor for the resolution of symptoms.

Complications

There are no complications associated with mesenteric adenitis as it resolves without intervention.

Pearls and Other Issues

These patients are oftentimes misdiagnosed with appendicitis and historically have undergone an unnecessary appendectomy.  This misdiagnosis occurs less often nowadays, thanks to improved diagnostic imaging and better clinical understanding of the disease.  

Enhancing Healthcare Team Outcomes

Achieving the correct diagnosis in these patients is vitally important and can help avoid unnecessary surgery.  It is important to take a detailed history and physical exam and be vigilant when evaluating for possible appendicitis and confirm on diagnostic imaging whether or not the appendix is well visualized and if it appears abnormal.  An incorrect diagnosis can lead to unnecessary invasive interventions to the patients with subsequent morbidities.