What is the appropriate diagnosis and treatment for small circular lesions on the abdomen?

Diagnosis and Management of Small Circular Lesions on the Abdomen

For small circular lesions on the abdomen, the first priority is determining whether these are superficial skin/abdominal wall lesions versus deeper intra-abdominal masses, which fundamentally changes the diagnostic and therapeutic approach.

Initial Diagnostic Strategy

Imaging Confirmation

• High-frequency ultrasound (5-12 MHz) is the first-line imaging modality for palpable abdominal wall lesions, as it can clearly differentiate the layers of the abdominal wall and distinguish superficial from deep lesions with high accuracy 1.
• If ultrasound confirms a superficial abdominal wall mass, contrast-enhanced CT should be performed to fully characterize the lesion, assess its relationship to surrounding structures, and determine if it represents an intramural versus extramural process 2.
• For lesions >5 cm or any deep lesions, imaging must be completed before any surgical intervention 2.

Differential Diagnosis by Location

Superficial Abdominal Wall Lesions:

• The most common abdominal wall lesions are hernias, which can present as circular masses and must be excluded first 1, 3.
• Fat-containing masses (lipomas) are the most common true abdominal wall masses 3.
• Fluid collections (seromas, hematomas, abscesses) appear as cystic lesions 1, 3.
• Solid masses include desmoid tumors, sarcomas, endometriomas, and metastases 3.

Intra-abdominal Subepithelial Lesions:

• If imaging reveals the lesions are within the gastrointestinal tract wall, gastrointestinal stromal tumors (GISTs) are the most common intramural subepithelial masses in the upper GI tract 4, 5.
• Gastric carcinoids (neuroendocrine tumors) present as small circular lesions and are classified into three types based on underlying pathology 6.
• Leiomyomas, granular cell tumors, lipomas, and pancreatic rests are other considerations 6.

Size-Based Management Algorithm

For Lesions <1 cm:

• Gastric subepithelial lesions <1 cm can be surveilled without resection if they appear benign 6.
• Type 1 gastric carcinoids <1 cm that are completely resected do not require further surveillance 6.
• Subcentimeter liver lesions in patients with primary malignancy are metastatic in only 12-22% of cases 6.

For Lesions 1-2 cm:

• Gastric GISTs ≤2 cm without high-risk features should undergo annual endoscopic ultrasound (EUS) surveillance, with initial follow-up at 6 months 6, 5.
• Type 1 gastric carcinoids 1-2 cm should be considered for endoscopic mucosal resection (EMR) 6.
• EUS-guided fine needle biopsy (FNB) should be performed to distinguish GIST from leiomyoma, as asymptomatic leiomyomas do not require surveillance or resection 6.

For Lesions ≥2 cm:

• GISTs ≥2 cm should be considered for resection due to increasing malignant potential 6, 4.
• Gastric GISTs 2-5 cm with low mitotic index have 3% metastasis risk, increasing to 16% with high mitotic index 6.
• For masses >3 cm, core needle biopsy using 14-16 gauge automated cutting needles is the standard approach, obtaining 4-6 cores while varying the angle to ensure adequate sampling 2.

High-Risk Features Requiring Immediate Action

Proceed directly to resection without surveillance if any of the following are present:

• Ulceration, bleeding, or symptomatic lesions 6.
• Irregular borders, cystic spaces, or echogenic foci on EUS 6.
• High mitotic index (>5 per 5 mm²) 5.
• Non-gastric location (small intestinal GISTs have up to 50% metastasis risk even when <2 cm) 6.

Tissue Diagnosis Requirements

When to Biopsy:

• Obtain tissue diagnosis via EUS-guided FNA or core needle biopsy for tumors ≥2 cm or any size with high-risk features before definitive surgery 5.
• Use image guidance (CT or ultrasound) to avoid necrotic areas and target viable tumor tissue 2.
• All diagnostic procedures should be discussed within a multidisciplinary tumor board before proceeding 2.

When to Avoid Biopsy:

• Small superficial masses amenable to simple laparoscopic excision 2.
• Cystic masses at high risk for peritoneal contamination 2.
• Emergency presentations requiring immediate surgical intervention 2.

Essential Pathologic Workup

For suspected GISTs, immunohistochemistry is mandatory:

• CD117 (c-kit) is positive in 95% of GISTs 4, 5.
• If CD117 is negative, immediately perform DOG1 staining, which identifies the remaining 5% of CD117-negative GISTs 4, 5.
• CD34 is positive in 70% of cases, providing supportive evidence 4.
• Tissue samples must be fixed in formalin (never Bouin fixation) to preserve molecular analysis capability 2.

Surgical Principles

For resectable lesions requiring surgery:

• Complete resection with negative (R0) margins is the primary goal 4, 5.
• Wedge resection of the stomach is adequate for most gastric GISTs, preserving gastric function 5.
• Avoid tumor rupture, as intra-abdominal spillage dramatically increases recurrence risk 4.
• Surgery should be performed by appropriately trained surgeons in or linked to a sarcoma specialist center 4.

Common Pitfalls to Avoid

• Do not skip contrast administration on CT unless absolute contraindications exist, as it significantly improves lesion characterization 2.
• Do not perform excessive cold biopsy forceps sampling or partial resection of colonic lesions, as this promotes scarring that makes subsequent curative resection more difficult 6.
• Do not proceed with definitive surgery before obtaining tissue diagnosis for larger masses requiring multivisceral resection, as this allows proper surgical planning and may avoid unnecessary surgery for non-surgical diseases like lymphoma 2.
• For gastric subepithelial lesions with endoscopic appearance consistent with lipoma or pancreatic rest and normal mucosal biopsies, further evaluation or surveillance is not needed 6.