What is the diagnosis and treatment for a painful cyst on the left side of the buttocks area, causing inability to sit and severe pain?

Differential Diagnoses for Painful Cyst on Left Buttock

The most likely diagnosis is a pilonidal cyst or abscess, which requires incision and drainage as the primary treatment, with antibiotics reserved only for systemic infection signs. 1

Primary Differential Diagnoses

Pilonidal Cyst/Abscess (Most Likely)

• Pilonidal disease classically presents as a painful, inflamed cyst in the gluteal cleft or buttock area that prevents sitting due to severe pain 1
• Look for a draining tract or "tail" (sinus opening) near the midline, which is pathognomonic for pilonidal disease 1
• The cyst originates from hair follicles and typically occurs in the sacrococcygeal region or upper buttock 1
• Pain severity that prevents sitting is characteristic of acute pilonidal abscess formation 1

Epidermoid Inclusion Cyst

• Can occur in the perineal and buttock region as a rare entity 2
• Presents as a protruding, painful mass when inflamed or infected 2
• May originate from deeper tissue planes including the intersphincteric space 2

Perirectal/Perianal Abscess

• Consider if the cyst is located closer to the anal verge rather than the upper buttock 3
• Presents with severe localized pain, swelling, and inability to sit comfortably 3
• May have associated fever, erythema, and fluctuance on examination 3

Gluteal Abscess (Soft Tissue Infection)

• Can present as a painful, fluctuant mass in the buttock area 3
• Look for signs of cellulitis: erythema, warmth, induration extending beyond the cyst 3
• Systemic signs include fever >38°C, tachycardia >90 bpm, leukocytosis >12,000 cells/µL 1

Critical Clinical Features to Evaluate

Signs Requiring Urgent Intervention

• Fever, tachycardia, tachypnea, or leukocytosis indicate systemic infection requiring antibiotics in addition to drainage 1
• Fluctuance on palpation confirms abscess formation requiring immediate incision and drainage 1
• Erythema and warmth extending >2 cm beyond the cyst margin suggests cellulitis 3

Anatomic Location Details

• Midline sacrococcygeal or gluteal cleft location strongly suggests pilonidal disease 1
• Lateral buttock location may indicate epidermoid cyst or soft tissue abscess 2
• Proximity to the anus (<5 cm) raises concern for perirectal abscess 3

Immediate Management Algorithm

Step 1: Clinical Assessment

• Measure vital signs to detect fever (>38°C), tachycardia (>90 bpm), or tachypnea (>20/min) 1
• Examine for fluctuance by palpating the mass for fluid wave 1
• Identify any draining tracts, sinus openings, or visible "pits" in the skin 1
• Assess extent of surrounding erythema and induration 3

Step 2: Laboratory Evaluation (If Systemic Signs Present)

• Complete blood count to evaluate for leukocytosis >12,000 cells/µL 1
• C-reactive protein if concern for deep infection or osteomyelitis 4
• Gram stain and culture are NOT routinely recommended for simple pilonidal abscess 1

Step 3: Definitive Treatment

• Incision and drainage is the cornerstone treatment for acutely inflamed, draining pilonidal cyst 1
• Thoroughly evacuate all pus and probe the cavity to break up loculations 1
• Cover with dry sterile dressing only—avoid packing with gauze as it increases pain without improving healing 1
• Prescribe antibiotics ONLY if systemic infection signs are present (fever, tachycardia, tachypnea, leukocytosis) 1

Step 4: Imaging (Only If Diagnosis Uncertain)

• Ultrasound can confirm cystic nature and assess for deeper extension 4
• MRI is reserved for complex cases with suspected deep tissue involvement or recurrent disease 1
• CT is generally not necessary for straightforward pilonidal disease 4

Common Pitfalls to Avoid

• Do NOT prescribe empirical antibiotics without clear signs of systemic infection or cellulitis 1
• Do NOT pack the wound with gauze after drainage—this increases pain and does not improve outcomes 1
• Do NOT obtain routine cultures of drainage fluid—reserve for treatment failures or immunocompromised patients 1
• Do not assume all buttock cysts are benign—if there is fixation to deeper tissues, firm consistency, or duration >2 weeks without improvement, consider imaging to exclude malignancy 1
• Do not delay drainage in favor of antibiotic trial—abscess requires source control first 1

Follow-Up Considerations

• Arrange surgical consultation for definitive excision after acute inflammation resolves (typically 4-6 weeks post-drainage) 1
• Counsel patient on hygiene measures: keep area clean and dry, consider hair removal in the gluteal cleft 1
• Warn about recurrence risk (10-30% after simple drainage alone) and need for potential definitive surgical excision 1