Imaging for Pilonidal Cyst in the Sacral Area
Imaging is generally not required for pilonidal cyst diagnosis, as this is a clinical diagnosis based on physical examination findings of pits, sinuses, or abscesses in the sacrococcygeal region. 1
When Imaging May Be Indicated
Imaging should be considered only in specific clinical scenarios:
- Complex or recurrent disease where surgical planning requires mapping of sinus tract extent and identification of secondary openings 2
- Suspected complications including abscess formation, malignant transformation (rare but reported in chronic cases), or invasion of adjacent structures 3
- Atypical presentations where the diagnosis is uncertain and other pathology needs exclusion 4
Ultrasound as First-Line When Imaging Is Needed
Point-of-care ultrasound is the preferred initial imaging modality when assessment is warranted, as it can map sinus tract extent, identify abscess formation, and guide surgical approach without radiation exposure. 2
- Ultrasound effectively identifies whether the sinus is infected or has formed an abscess 2
- It helps surgeons tailor the surgical approach to individual cases by mapping disease extent 2
- Ultrasound is readily available, inexpensive, and can be performed at the bedside 2
MRI for Complex Cases
MRI should be reserved for complex cases where ultrasound is inadequate, particularly when there is concern for deep extension, sacral involvement, or malignant transformation. 3
- MRI provides superior soft tissue characterization and can evaluate for sacral bone destruction 3
- It is essential when invasion of adjacent structures (such as rectum) is suspected 3
- MRI can differentiate pilonidal disease from other sacral pathology including sacral cysts, which have characteristic fluid signal on T2-weighted sequences 5
CT Has Limited Role
CT is not routinely indicated for pilonidal cyst evaluation 4
- CT may be useful if malignant transformation is suspected and staging is required 3
- It provides excellent bone detail if sacral destruction is a concern 5
Important Clinical Distinctions
Pilonidal disease must be differentiated from hidradenitis suppurativa, which can coexist with inflammatory bowel disease and has different treatment implications. 4
- Pilonidal disease typically presents in the midline sacrococcygeal region with characteristic pits 1
- Hidradenitis suppurativa shows bilateral involvement, subcutaneous edema, and involvement of inguinal/gluteal areas 4
- When ultrasound is performed, perianal skin lesions should be reported using clock-face nomenclature 4
Common Pitfalls to Avoid
- Do not order imaging routinely for straightforward pilonidal disease—this is a clinical diagnosis requiring only physical examination 1
- Do not confuse pilonidal cysts with sacral cysts—sacral cysts show expansion of sacral foramina on imaging and have fluid density (5-20 Hounsfield units on CT) 5
- Do not miss malignant transformation in long-standing chronic cases—maintain high suspicion if there is rapid growth, bone destruction, or invasion of adjacent structures 3