Neurovasculature involvement (iliac and sacral vessels, cauda equina and sacral nerve roots)

Fig 4: Surgical approach based on Imaging findings

TAIL GUT AND RECTAL DUPLICATION CYSTS

• CT/ MR: Thin walled purely cystic usually unilocular retrorectal lesions.
• Rarely can be complicated with secondary hemorrhage, infection or proteinaceous content.
• Tail gut and rectal duplication cysts are identical on imaging and only differentiated histologically, with the later containing organized muscle layer including a well defined muscularis propria.
• The differentiation however is surgically irrelevant, as imaging information is sufficient for excision.
  

  Fig 5: Tail gut cyst

ANTERIOR SACRAL MENINGOCOELE (ASM)

• Congenital defect in the anterior aspect of the spine with herniation of meninges (dura-arachnoid) and CSF anteriorly into the pelvis.
• Homogeneous thin walled unilocular fluid/ CSF containing presacral lesion.
• MRI is the modality of choice providing details of the lesion, nerve roots and complications such as tethered cord, tumours or lipomas.
• CT allows the delineation of sacral alar and foraminal bony anatomy.
  

  Fig 6: Anterior Sacral meningocoele

SACROCOCCYGEAL TERATOMA

• Most common congenital tumor in the fetus and neonates.
• CT/ MR: mixed solid-cystic or predominantly cystic forms, with or without calcifications and fat content.
• Subclassified based on whether the bulk of the lesion is intrapelvic or extrapelvic : Altman system
• Histologically composed of all three germ cells (i.e. ectoderm, mesoderm and endoderm).
  

  Fig 7: Cystic Sacrococcygeal Teratoma

RETRORECTAL LYMPHANGIOMA

• well-defined multilocular cystic masses with typically homogeneous fluid content on CT/ MR.
• often "mesh like pattern" on USG seen due to multiple thin septations.
• usually uncomplicated, but rare secondary hemorrhages or infections may occur.
  

  Fig 8: Retrorectal Lymphangioma

SACROCOCCYGEAL CHORDOMA

• Most common primary malignant sacral neoplastic lesion (origin from the primitive notochord)
• CT : degree of bone lysis / sacral destruction & lesional calcification if present.
• MRI : Characterize the lesion, delineate the anatomy of adjacent structures, and detect internal hemorrhage.
• Typical macroscopic (mucoid-gelatinous) and microscopic (Physaliphorous cells) appearance
  

  Fig 9: Sacro-coccygeal Chordoma

RHABDOMYOSARCOMA

• Most common soft tissue tumor in children, however presacral location is uncommon
• CT/ MR: heterogeneous mixed solid-cystic lesion, with intense post contrast enhancement and relationship with adjacent structures
• Surprisingly often spares the sacral vertebral posteriorly, useful in diagnosis
• Typical microscopic appearance with Rhabdomyoblasts and nuclear pleomorphism
  

  Fig 10: Rhabdomyosarcoma

SACRAL NEUROGENIC TUMOR/ SCHWANNOMA-NEUROFIBROMA

• nerve sheath tumors within the spinal canal, typically arising from dorsal sensory nerve roots
• CT/ MR: solid or solid-cystic well defined lesions with bony remodelling/ foramen widening/ vertebral body scalloping. 
• Schwannoma often associated with internal vascular change or hemorrhage : seen as fluid levels
• Typical microscopic appearance with Antoni type A and B cells
  

  Fig 11: Sacral Neurogenic tumor