Sacrococcygeal Mass

Kevin R. Moore, MD

DIFFERENTIAL DIAGNOSIS

Common

Less Common

Rare but Important

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

Myriad pathologies produce sacrococcygeal masses
- Clinical data directs differential list
Fever, elevated inflammatory markers prompt search for infection source
Identification of tumor matrix narrows differential considerations
Location and relationship of mass to important regional structures impacts tumor resectability
Look for osseous invasion or epidural extension, which may alter surgical planning

Helpful Clues for Common Diagnoses

Sacrococcygeal Teratoma
- Very heterogeneous density/signal intensity, enhancement of solid tumor portions
- AAP grade based on proportion of external and internal tumor
- Worse outcome portended by
  - Male sex
  - Large proportion of internal tumor
  - Older age at diagnosis
- Often detected on routine obstetrical ultrasound elective cesarean section
  - Fetal MR valuable for confirmation of diagnosis, AAP grading
- Sacrum and coccyx usually spared, even when tumor spreads into spinal canal via sacral hiatus
- Coccyx must be resected or recurrence risk high
Presacral Abscess
- Fever, serum inflammatory markers usually elevated, prompting clinical consideration of diagnosis
- Regional soft tissue inflammation, discitis, epidural abscess, or vertebral osteomyelitis
- Rim enhancement and diffusion restriction on DWI MR characteristic

Helpful Clues for Less Common Diagnoses

Neuroblastic Tumor
- Paraspinal location along sympathetic chain (neural crest derivatives)
- Benign (ganglioneuroma) → intermediate grade (ganglioneuroblastoma) → highly malignant (neuroblastoma)
- Frequently calcified, encircles vessels and regional structures
- Important upstaging findings affecting surgical management include bilaterality and epidural extension
  - MR best imaging modality for detecting tumor extension into spinal canal through neural foramen
Plexiform Neurofibroma
- Neurofibromatosis type 1
- Grape-like or botryoid morphology with characteristic distribution along nerves (major or minor peripheral nerves/plexi)
- Hyperintense on STIR MR, T2WI MR
  - “Target” appearance
Lymphoma
- Protean imaging appearances
- Often large at diagnosis
- May be focal or diffuse
- Relatively low signal intensity on T2WI MR ± mild diffusion restriction reflects high tumor cellularity
Ewing Sarcoma
- Usually older child/adolescent presentation age
- Aggressive or permeative bone destruction
- Cellular signal intensity (relatively low signal intensity on T2WI MR)

Helpful Clues for Rare Diagnoses

Rhabdomyosarcoma
- Aggressive soft tissue mass with frequent bone invasion
- Rarely arises primarily in sacrum
  - Usually regional extension from prostate or uterus primary tumor
- Signal characteristics variable
  - Frequently shows cellular characteristics with lower signal intensity on T2WI MR
Osteosarcoma
- Destructive lesion with frank bone destruction and large soft tissue mass
- May arise in preexisting lesion (aneurysmal bone cyst, fibrous dysplasia)
- Osteoid matrix makes diagnosis
Dermoid and Epidermoid Tumors
- Consider previous lumbar puncture with nonstyletted needle, congenital dermal sinus tract
- Contains fat &/or squamous debris
- Epidermoid component diffusion restriction
  
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