Rare Causes of Appendicitis: Beyond the Common Suspects

Appendicitis: Common Causes Overview

Appendicitis represents one of the most common surgical emergencies worldwide, characterized by inflammation of the vermiform appendix. The conventional understanding attributes most cases to two primary mechanisms: fecalith obstruction and lymphoid hyperplasia. Fecaliths, which are hardened accumulations of fecal material, account for approximately 30-40% of appendicitis cases in Hong Kong according to surgical data from the Hospital Authority. These calcified masses effectively block the appendiceal lumen, creating an environment conducive to bacterial overgrowth and subsequent inflammation. Lymphoid hyperplasia, the second major cause, typically occurs in response to viral or bacterial infections elsewhere in thebody, causing swelling of the lymphoid tissue within the appendix wall. This mechanism proves particularly prevalent among younger patients, with Hong Kong's paediatric surgical units reporting lymphoid hyperplasia as the dominant cause of appendicitis in patients under 20 years old.

The pathophysiology of conventional appendicitis follows a predictable pattern: obstruction leads to increased intraluminal pressure, compromised blood flow, bacterial proliferation, and eventual inflammation that can progress to ischemia, perforation, and peritonitis if left untreated. This standard progression explains why the condition demands prompt surgical intervention. However, the medical community increasingly recognizes that not all appendicitis cases conform to this typical presentation. The diagnostic challenge intensifies when patients present with atypical symptoms or belong to demographic groups where appendicitis is less common, such as the very young or elderly populations. Understanding the complete spectrum of potential triggers, including rare causes, becomes crucial for accurate diagnosis and appropriate management. The cause of appendicitis in these unusual scenarios often requires different diagnostic approaches and may significantly alter treatment strategies, particularly when underlying conditions like tumors or systemic diseases are involved.

Focusing on Rarer, Less-Known Causes

While the majority of appendicitis cases stem from the common mechanisms previously described, medical literature and clinical experience reveal a fascinating array of unusual triggers that can initiate the inflammatory cascade. These rare causes collectively account for approximately 5-8% of appendicitis cases in Hong Kong's surgical statistics, yet their identification carries profound implications for patient outcomes. The diagnostic process becomes particularly challenging when these unusual triggers mimic conventional appendicitis in their clinical presentation but demand fundamentally different management approaches. Surgeons and physicians must maintain a high index of suspicion for these atypical etiologies, especially when intraoperative findings contradict the preoperative diagnosis or when patients present with recurrent or persistent right lower quadrant pain despite previous appendectomy.

The clinical significance of recognizing these rare causes extends beyond academic interest. Failure to identify an underlying tumor, parasitic infection, or vascular abnormality as the true cause of appendicitis can lead to incomplete treatment, disease recurrence, or missed opportunities to address potentially serious systemic conditions. For instance, when appendiceal carcinoid tumors masquerade as simple appendicitis, the surgical approach may need modification to ensure complete tumor excision with adequate margins. Similarly, parasitic infections causing appendiceal inflammation require specific antihelminthic therapy in addition to surgical intervention to prevent recurrence. The cause of appendicitis in these scenarios demands careful investigation and often necessitates collaboration between surgeons, pathologists, and infectious disease specialists to ensure comprehensive patient care.

Tumors and Their Impact on Appendiceal Health

Neoplastic processes represent one of the most clinically significant yet underrecognized categories among unusual appendicitis triggers. Appendiceal tumors account for approximately 0.5-1% of all gastrointestinal neoplasms, with Hong Kong Cancer Registry data indicating an incidence of approximately 0.12 cases per 100,000 population annually. Despite their rarity, these tumors frequently present as acute appendicitis, creating diagnostic dilemmas that often only resolve during histopathological examination of the resected specimen. The mechanical effects of tumor growth—including luminal obstruction, wall infiltration, and compromised blood supply—create ideal conditions for secondary inflammation and infection that mimic conventional appendicitis.

Carcinoid tumors constitute the most common primary neoplasm of the appendix, representing about 50-80% of all appendiceal tumors. These neuroendocrine tumors typically arise from enterochromaffin cells in the submucosa and most frequently locate at the tip of the appendix. While most carcinoids measure less than 1 cm and remain asymptomatic, larger lesions (exceeding 2 cm) can obstruct the appendiceal lumen or incite a desmoplastic reaction that compromises appendiceal mobility and blood flow. The clinical presentation often mirrors uncomplicated appendicitis, though some patients may experience carcinoid syndrome symptoms if liver metastases are present. Surgical management depends on tumor size and location, with simple appendectomy sufficing for tumors smaller than 1-2 cm located at the tip, while larger tumors or those involving the base may require right hemicolectomy.

Adenocarcinomas of the appendix, though exceptionally rare, represent another important tumor-related cause of appendicitis. These malignancies can be classified into mucinous and non-mucinous variants, with the former having particular clinical significance due to their potential for pseudomyxoma peritonei. Mucinous adenocarcinomas often produce abundant mucus that distends the appendiceal lumen, creating a mucocele that can secondarily obstruct drainage and initiate inflammation. The diagnostic challenge lies in distinguishing these tumors preoperatively from simple appendiceal inflammation, as imaging findings may be nonspecific. Treatment typically involves right hemicolectomy, especially for tumors demonstrating high-grade features or perforation. Other tumor types including lymphomas, gastrointestinal stromal tumors (GISTs), and secondary metastases from distant primaries can similarly initiate appendicitis through mass effect or wall infiltration, though these occurrences are exceptionally rare in clinical practice.

Parasitic Infections and Appendiceal Inflammation

Parasitic infestations constitute another category of unusual triggers for appendicitis, with geographical variations in prevalence reflecting local sanitation standards and public health infrastructure. In Hong Kong, despite generally high hygiene standards, parasitic infections still account for approximately 1-2% of appendicitis cases according to pathology department reviews from major hospitals. The mechanism by which parasites induce appendicitis typically involves direct luminal obstruction, mucosal irritation, or secondary bacterial infection facilitated by the parasitic presence. The clinical presentation often resembles conventional appendicitis, though some patients may report additional symptoms such as perianal itching, visible worms in stool, or eosinophilia on blood tests that provide diagnostic clues.

Enterobius vermicularis, commonly known as pinworm, represents the most frequently identified parasitic cause of appendicitis in temperate regions including Hong Kong. These small nematodes typically inhabit the cecum and ascending colon, with female worms migrating to the perianal region at night to deposit eggs. When pinworms invade the appendix—occurring in approximately 0.2-4% of appendectomy specimens in endemic areas—they can incite inflammation through several mechanisms. The worms themselves may physically obstruct the narrow appendiceal lumen, while their movement and attachment to the mucosa can cause mechanical irritation and inflammatory responses. Additionally, the presence of dead worms or eggs can serve as nidi for fecalith formation or act as foreign bodies that trigger intense local immune reactions. Histopathological examination typically reveals eosinophilic infiltration of the appendiceal wall, sometimes with visible cross-sections of adult worms containing characteristic laterally-aligned eggs.

Other parasitic infections with documented association to appendicitis include Ascaris lumbricoides (roundworm) and Trichuris trichiura (whipworm), though these occur less frequently in urban settings like Hong Kong. Ascaris can cause appendicitis when individual worms migrate into and obstruct the appendiceal lumen, while heavy Trichuris infestations may extend from the cecum into the appendix, causing mucosal damage and inflammation. Schistosomiasis, though uncommon in Hong Kong, represents another parasitic cause through egg deposition in appendiceal tissues inciting granulomatous inflammation. The diagnostic approach to parasitic appendicitis should include thorough history-taking regarding travel, exposure risks, and household contacts, while treatment necessitates both surgical intervention for the acute inflammation and specific antihelminthic therapy to eradicate the underlying infestation.

Vascular Abnormalities Affecting the Appendix

Vascular pathologies represent perhaps the rarest category among unusual appendicitis triggers, yet their recognition is crucial as they may indicate underlying systemic disorders. The appendix, like other hollow organs, depends on adequate blood supply through the appendicular artery—a branch of the ileocolic artery—for mucosal integrity and normal function. Compromise of this vascular supply, whether through mechanical factors or inflammatory processes, can initiate ischemic changes that progress to inflammation and necrosis indistinguishable from obstructive appendicitis. The clinical challenge lies in identifying these vascular etiologies preoperatively, as they often present with identical symptoms to conventional appendicitis but may require different management strategies.

Appendiceal torsion, though exceptionally rare, represents a dramatic vascular cause of appendicitis characterized by twisting of the appendix around its mesenteric pedicle. This rotation compromises venous outflow and eventually arterial inflow, leading to hemorrhagic infarction and subsequent inflammation. Torsion may occur spontaneously or in association with anatomical variations such as excessively long mesoappendix, appendiceal neoplasms, or adhesions from previous surgeries. The diagnosis is almost invariably made intraoperatively, with findings including a darkened, congested appendix with obvious twisting of its vascular pedicle. Treatment involves detorsion (if viable) followed by appendectomy, though the ischemic damage often renders the organ non-viable by presentation.

Vasculitides affecting medium and small vessels represent another vascular mechanism for appendicitis, with the appendix occasionally serving as the initial presentation site for systemic disorders. Polyarteritis nodosa, Henoch-Schönlein purpura, Behçet's disease, and other vasculitides can involve the appendiceal vessels, causing ischemic changes through inflammation and thrombosis of the vasa vasorum. The histological findings in these cases typically include fibrinoid necrosis of vessel walls, leukocytoclasis, and perivascular inflammatory infiltrates distinct from the changes seen in conventional appendicitis. Patients may have extracolonic manifestations suggesting systemic involvement, such as skin lesions, arthralgias, or renal abnormalities. Management requires both appendectomy for the acute abdominal condition and systemic treatment of the underlying vasculitis, typically with corticosteroids and immunosuppressants. Other vascular causes including thrombosis in hypercoagulable states, embolic phenomena from cardiac sources, or vasculopathy associated with connective tissue disorders have also been rarely reported as initiators of appendiceal inflammation.

Diagnostic Challenges and Specialized Testing

The identification of unusual appendicitis triggers presents significant diagnostic challenges that often require a multidisciplinary approach. Conventional imaging modalities including ultrasound and computed tomography (CT) excel at diagnosing appendicitis generally but frequently fail to delineate the specific underlying cause, particularly for rare etiologies. CT scanning demonstrates approximately 90-95% sensitivity for detecting appendiceal inflammation in Hong Kong hospital studies, but its specificity for determining the precise etiology rarely exceeds 70% for unusual causes. The radiologic features that might suggest an unusual cause of appendicitis include atypical patterns of wall thickening, unexpected calcifications, associated lymphadenopathy, or involvement of other bowel segments.

When clinical suspicion exists for an unusual cause of appendicitis, additional investigations may prove valuable. Serological testing for inflammatory markers including C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) can provide clues to systemic conditions like vasculitis. Eosinophilia on complete blood count may suggest parasitic infestation or certain drug reactions. Stool examinations for ova and parasites should be considered in patients with appropriate epidemiological risk factors or suggestive symptoms. For suspected neoplasms, tumor markers such as carcinoembryonic antigen (CEA) or chromogranin A may offer supportive evidence, though their diagnostic utility in acute presentations remains limited. The definitive diagnosis of unusual appendicitis causes typically requires histopathological examination of the resected specimen, emphasizing the importance of thorough pathological assessment in all appendectomy cases.

Clinical Implications and Management Considerations

Recognizing the possibility of unusual appendicitis triggers carries profound implications for patient management and outcomes. When intraoperative findings suggest an unexpected etiology—such as a palpable mass, unusual appearance, or associated pathological features—the surgical approach may require modification. Frozen section analysis can provide immediate guidance regarding potential neoplasms, while extended resection may be necessary for confirmed malignancies. The identification of parasitic infections should prompt postoperative antihelminthic treatment and consideration of household contact screening. When vasculitis is suspected, rheumatology consultation and appropriate serological testing become essential components of comprehensive care.

The long-term follow-up requirements also differ significantly based on the underlying cause of appendicitis. Patients with appendiceal neoplasms require appropriate oncological surveillance, while those with vasculitis need monitoring for systemic involvement and medication side effects. For parasitic causes, confirmation of eradication through follow-up stool examinations may be indicated. These considerations highlight that appendicitis, while common, should not be viewed as a uniformly straightforward condition. Maintaining awareness of the full spectrum of potential triggers ensures that patients receive appropriately tailored management that addresses not just the acute inflammation but also any underlying pathological processes. This comprehensive approach ultimately leads to improved patient outcomes and reduces the likelihood of missed diagnoses with potentially serious consequences.

Epidemiological Patterns in Hong Kong

Understanding the local epidemiological patterns of unusual appendicitis causes provides valuable context for clinicians practicing in specific regions. Hong Kong's unique position as a densely populated international hub with high healthcare standards creates an interesting epidemiological profile for appendicitis. According to data from the Hospital Authority spanning 2015-2020, the overall incidence of appendicitis in Hong Kong remains consistent with global figures at approximately 100 cases per 100,000 population annually. However, the distribution of unusual causes demonstrates some distinctive patterns:

• Tumor-associated appendicitis: 0.8% of cases, with carcinoids representing 65% of these
• Parasitic appendicitis: 1.2% of cases, predominantly Enterobius vermicularis
• Vascular causes: 0.3% of cases, with vasculitis representing the majority
• Other rare causes (foreign bodies, endometriosis, etc.): 0.7% of cases

These figures highlight that while unusual causes collectively account for only about 3% of appendicitis cases in Hong Kong, their absolute numbers remain significant given the population base. Furthermore, certain subgroups demonstrate different patterns—parasitic appendicitis shows higher prevalence in pediatric populations and recent immigrants from endemic regions, while tumor-associated cases increase with age. This epidemiological understanding helps clinicians maintain appropriate suspicion for unusual causes based on patient demographics and presentation features, ensuring that rare but important etiologies receive consideration in the diagnostic process. The cause of appendicitis in these unusual scenarios often reflects both local epidemiological factors and individual patient characteristics, requiring clinicians to balance population statistics with personalized assessment.