Diagnostic Ultrasound - Abdomen and Pelvis

Appendiceal Mucocele
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Diagnoses: Bowel
• Infiltrative mass ± enlarged nodes
Obstructive Acute Appendicitis
• Peri appendiceal echogenic fat
• Focal tenderness and clinical findings
Mesenteric Cyst
• Usually lymphangioma
• Closely associated with bowel wall
• Septations seen on ultrasound and MR
Distended Meckel Diverticulum
• Appendix identified separately
• Fluid-filled tubular structure with base in antimesenteric
border of distal ileum
PATHOLOGY
General Features
• Etiology
○ Commonly caused by epithelial proliferation, which
could be benign or malignant
○ Less commonly secondary to obstructive causes
– Fecalith or appendicolith
– Inflammatory or fibrotic narrowing
– Rarely from deep infiltrative endometriosis
Staging, Grading, & Classification
• Simple mucocele secondary to inflammation and
nonneoplastic obstruction (simple retention cysts)
○ Rarely exceed 2.0 cm in diameter
• Mucocele secondary to
○ Focal or diffuse mucosal hyperplasia
○ Low-grade mucinous cystadenoma (low-grade
appendiceal mucinous neoplasm [LAMN])
○ Mucinous cystadenocarcinoma
• Classification of appendiceal mucinous neoplasms is
controversial and terminology inconsistent
• Simple mucocele and mucocele secondary to mucosal
hyperplasia are referred to as nonneoplastic mucocele
• Mucocele secondary to LAMN is referred to as benign
neoplastic mucocele
• Mucocele secondary to mucinous cystadenocarcinoma is
referred to as malignant mucocele
Gross Pathologic & Surgical Features
• Round or oval cystic mass with thick fibrous capsule
• Lumen filled with translucent yellowish mucoid fluid
CLINICAL ISSUES
Presentation
• Most common signs/symptoms
○ Frequently discovered incidentally
– Asymptomatic in 25% patients
○ Most common presentation is right lower quadrant pain
or palpable mass
– Found in up to 50% patients
• Other signs/symptoms
○ Superinfection of tumoral mucocele may clinically
resemble nontumoral acute appendicitis
○ Simple mucoceles secondary to obstruction and
inflammation can clinically present as acute appendicitis
○ Rarely presents as intussusception
Demographics
• Age
○ Middle aged or older
• Gender
○ More frequent in females
• Epidemiology
○ Reported prevalence in appendectomy specimens is 0.2-
0.3%
Natural History & Prognosis
• Pseudomyxoma peritonei (PMP): Serious complication of
spontaneous or iatrogenic rupture of appendicular
mucocele, which could be benign or malignant
○ Incidence of perforation and PMP is ~ 20% in benign
mucinous cystadenomas and 6% in malignant
cystadenocarcinoma
• Appendiceal mucocele is associated with increased
incidence of colon adenocarcinoma
Treatment
• Options, risks, complications
○ Treatment of choice for simple mucocele is
appendectomy
○ Cecectomy is performed for benign mucoceles
○ Right hemicolectomy is performed for mucinous
cystadenocarcinoma
– Open laparotomy is preferred to avoid perforation,
which has risk of pseudomyxoma peritonei
○ Preoperative differentiation of benign and malignant
mucoceles challenging
– Irregular wall and internal soft tissue nodularity of
mucoceles suggestive of malignant mucoceles
– Frozen section useful
DIAGNOSTIC CHECKLIST
Consider
• Appendicular mucocele in differential diagnosis of cystic
right lower quadrant mass
Image Interpretation Pearls
• Cystic tubular or pear-shaped cystic structure in right lower
quadrant
• Base indistinguishable from appendix
• Calcification in wall suggestive of appendicular mucocele
• Echogenic contents with onion skin sign on ultrasound
specific for appendicular mucocele
• Appendicolith seen at base in simple appendicular
mucocele of obstructive type
• Irregular wall and internal soft tissue nodularity of
mucoceles suggestive of malignant mucocele
SELECTED REFERENCES
1. Attarde V et al: Sonographic appearance of a giant appendicular mucocele. J
Clin Ultrasound. 39(5):290-2, 2011
2. Caspi B et al: The onion skin sign: a specific sonographic marker of
appendiceal mucocele. J Ultrasound Med. 23(1):117-21; quiz 122-3, 2004
3. Wang H et al: Appendiceal mucocele: A diagnostic dilemma in differentiating
malignant from benign lesions with CT. AJR Am J Roentgenol. 201(4):W590-
5, 2013
4. Pickhardt PJ et al: Primary neoplasms of the appendix: radiologic spectrum
of disease with pathologic correlation. Radiographics. 23(3):645-62, 2003