What is the differential diagnosis for a 2 mm movable and firm lump located in the male groin, adjacent to but not on or in the scrotum?

Differential Diagnosis for 2 mm Movable Groin Lump Adjacent to Scrotum

The most likely diagnosis is a benign extratesticular lesion, most commonly a lipoma, adenomatoid tumor, or lymph node, given the small size, mobility, and location outside the scrotum. 1, 2

Initial Diagnostic Approach

Scrotal ultrasound with Doppler is the mandatory first-line imaging study to definitively determine whether this lump is intratesticular, extratesticular, or inguinal in origin. 1, 3 The ACR guidelines emphasize that ultrasound is nearly 100% sensitive for detecting intrascrotal masses and 98-100% accurate for distinguishing intratesticular from extratesticular processes. 1

Key Clinical Distinctions to Assess

• Location specificity: Confirm whether the mass is truly extratesticular/paratesticular versus an inguinal lymph node, as the groin region contains both scrotal and inguinal structures. 1
• Mobility and fixation: Mobile masses favor benign processes like lipomas or lymph nodes, while fixed masses raise concern for malignancy. 1
• Associated symptoms: Absence of pain, skin changes, or systemic symptoms favors benign etiology. 4

Most Likely Differential Diagnoses

Benign Extratesticular Masses (Most Common)

Approximately 90% of extratesticular masses are benign, in stark contrast to intratesticular masses where 90% are malignant. 3, 2

• Lipoma of spermatic cord: The most common extratesticular neoplasm, typically mobile and firm. 2, 5
• Adenomatoid tumor: Most often found in the epididymis, benign mesothelial origin. 2, 5
• Scrotal leiomyoma: Rare benign tumor arising from dartos muscle layer, typically firm and mobile. 6
• Lymphangioma circumscriptum: Rare hamartomatous lymphatic malformation that can occur in scrotal/groin region. 7

Inguinal Lymph Node

• Reactive lymph node: Given the location "adjacent to scrotum" in the groin, this could represent an inguinal lymph node, which can be palpable normally or reactive to minor inflammation. 1
• Size consideration: At 2 mm, this is quite small for clinical significance; inguinal lymph nodes become concerning when >2-4 cm. 1

Less Likely but Important Considerations

• Epididymal cyst or spermatocele: Though typically within scrotal sac, can be palpated at periphery. 4, 5
• Fibrous pseudotumor: Benign reactive fibrous proliferation. 2, 5

Critical Management Algorithm

Step 1: Obtain Scrotal/Inguinal Ultrasound with Doppler

This is non-negotiable for any palpable groin or scrotal mass. 1, 3 The ultrasound will definitively characterize:

• Solid versus cystic nature
• Intratesticular versus extratesticular location
• Vascular flow patterns
• Relationship to surrounding structures

Step 2: Risk Stratification Based on Imaging

If extratesticular and benign-appearing on ultrasound:

• Most require no treatment beyond observation. 4, 5
• Clinical follow-up to ensure stability. 6

If any concern for intratesticular involvement:

• Obtain serum tumor markers (AFP, β-HCG, LDH) before any intervention. 1, 3
• Urgent urology referral, as any solid intratesticular mass must be managed as malignant until proven otherwise. 1, 3

If inguinal lymph node with concerning features:

• Assess for primary malignancy risk factors (cryptorchidism, testicular atrophy, family history). 3
• Consider fine-needle aspiration if node >2 cm or has suspicious characteristics. 1

Critical Pitfalls to Avoid

• Never assume a groin mass is benign without imaging confirmation, even if small and mobile. 1, 3
• Never perform scrotal approach biopsy for any suspected testicular tumor, as this violates lymphatic drainage patterns. 3
• Do not delay evaluation if the mass changes in size, becomes fixed, or develops associated symptoms. 3, 4
• Recognize that malignant extratesticular tumors do exist (rhabdomyosarcoma, liposarcoma, leiomyosarcoma) and are often large at presentation, though rare. 2

Specific Considerations for This Case

Given the 2 mm size, firm consistency, and mobility, this most likely represents either:

1. A small inguinal lymph node (normal or reactive)
2. A small lipoma or other benign extratesticular lesion

The small size (2 mm) is reassuring, as malignant processes typically present larger. 1, 2 However, ultrasound confirmation remains essential to exclude any intratesticular component and provide definitive characterization. 1, 3