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KEY FACTS

Terminology
- Hernia through defect in aponeurosis of internal oblique and transverse abdominal muscles
Imaging
- Hernia occurs along lateral border of rectus abdominis muscles, inferior/lateral to umbilicus, at level of arcuate line - Occurs at or below arcuate line due to lack of posterior rectus sheath at this level - Lies deep to external oblique aponeurosis and muscle - 90% within Spigelian belt, 6-cm transverse band above line joining anterior superior iliac spines
- Most often contains portions of greater omentum, small bowel, or colon - Rarely can involve appendix, bladder, and other abdominal/pelvic structures
- Defect size is usually small (usually < 2 cm), resulting in narrow hernia neck and high risk of strangulation
Top Differential Diagnoses
- Other abdominal wall hernias
- Subcutaneous or intramuscular lipoma
- Subcutaneous masses, fluid collections, or hematoma
Pathology
- Probably multifactorial etiology, including congenital weakness of Spigelian fascia - Usually congenital in children and acquired in adults - Prior history of abdominal surgery and obesity are biggest risk factors in adults - Other risk factors include multiple pregnancies, rapid weight loss, COPD, and trauma
Clinical Issues
- Rare hernia that accounts for 1-2% of anterior abdominal wall hernias
- Difficult to diagnose clinically due to deep anatomic location, especially in obese patients
- Most common symptoms are pain and palpable bulge most apparent when standing
- Surgical treatment indicated in virtually all patients due to high risk of strangulation and incarceration

TERMINOLOGY

Abbreviations
- Spigelian hernia (SH)
Synonyms
- Lateral ventral hernia; anterolateral hernia; hernia through conjoint tendon
Definitions
- Hernia through defect in aponeurosis of internal oblique and transverse abdominal muscles - Spigelian aponeurosis: Aponeurosis of internal oblique and transverse abdominal muscles

IMAGING

General Features

Best diagnostic clue

- Hernia located lateral to rectus muscle and caudal/lateral to umbilicus, which is covered by intact external oblique muscle

Location

- Hernia sac extends through defect in aponeurosis of transverse abdominal and internal oblique muscles
        - Typically at or below level of arcuate line = semicircular line
                  - Occur at or below arcuate line due to lack of posterior rectus sheath at this level
        - Lies deep to external oblique aponeurosis
                  - External oblique aponeurosis usually remains intact (hernial sac is intermuscular)
        - Occurs along lateral border of rectus abdominis muscles, inferior and lateral to umbilicus, at level of arcuate line
        - 90% of SHs are within **Spigelian belt of Spangen**, 6-cm transverse band above line joining both anterior superior iliac spines
- 2 primary types
        - **Interstitial or interparietal SH**: Located below major oblique muscle among muscle layers of abdominal wall
                  - By far most common (98% of cases)
        - **Subcutaneous SH**: Hernia sac crosses major oblique aponeurosis and becomes superficial (crosses beyond muscle layer of wall)
                  - Very rare
- May have slight left-sided predominance, although exact reason is unknown

Morphology

- Defect size range: 1- to 7.5-cm diameter (most defects small and < 2 cm in size)
- Most often contains portions of greater omentum, small bowel, or colon
        - Rarely can involve appendix, bladder, and other abdominal/pelvic structures

CT Findings
- Hernia defect in aponeurosis of transverse abdominal and internal oblique muscles
- Lateral to rectus sheath, caudal to umbilicus, and deep to external oblique muscle and fascia
- Herniation of omentum ± bowel loops
Imaging Recommendations
- Best imaging tool
```
- CECT
```
Ultrasonographic Findings
- Begin at lateral margin of rectus abdominis in transverse plane at umbilicus - As transducer is moved inferiorly, inferior epigastric artery can be identified - SH can be visualized along linea semilunaris
- Cough and Valsalva maneuver during exam may help increase conspicuity of hernia

DIFFERENTIAL DIAGNOSIS

Ventral Hernia
- Majority occur through midline aponeurosis
- Incisional hernia through off-midline incision can mimic SH
- No intact external oblique muscle or fascia
Umbilical Hernia
- Bowel, fat, or ascites protruding through umbilical defect in midline
- SHs occur inferior and lateral to umbilicus
Hernia Through Laparoscopy Port
- Usually smaller defect and tend to be located medial or lateral to spigelian site
Rectus Sheath Hematoma
- Cylindrical, heterogeneous mass within sheath without true fascial defect or hernia
- Easily differentiated from hernia on CT
Subcutaneous or Intramuscular Lipoma
- Should be easily distinguished from hernia on CT

PATHOLOGY

General Features

Etiology

- Probably multifactorial etiology, including congenital weakness of Spigelian fascia
        - Abdominal wall at site of SH intrinsically weak due to lack of posterior sheath behind rectus muscle
        - Usually congenital defect in children and infants
        - Usually acquired defects in adults
- Prior history of abdominal surgery and obesity are biggest risk factors in adults for development of SH
        - Other risk factors include multiple pregnancies, rapid weight loss, COPD, and trauma

Associated abnormalities

- Undescended testis (17%) in children; ipsilateral
- Other anterior wall defects (e.g., omphalocele, bladder extrophy, prune belly)
- Coexisting ventral, inguinal, umbilical hernia

Gross Pathologic & Surgical Features
- Interparietal or interstitial herniation (i.e., hernias cross transversus abdominis and internal oblique muscles but are behind external oblique aponeurosis)
- Contents: Omentum ± short segment of small or large bowel

CLINICAL ISSUES

Presentation
- Can be asymptomatic
- Most common symptoms are pain and palpable bulge or mass, usually most apparent when standing
- Symptoms of bowel obstruction due to high predisposition for incarceration
- Difficult to diagnose clinically due to deep anatomic location, especially in obese patients

Demographics

Age
```
- Patients between 40-70 years of age
```

Sex

- Children: M:F = 2:1
- Essentially equal among adults, although possibly very minimal female predominance

Epidemiology

- Accounts for 1-2% of anterior abdominal hernias
- Bilateral hernia: 15% incidence in children

Natural History & Prognosis
- Omentum within SH may infarct and cause symptoms
- Hernia defect tends to be tight with narrow diameter of hernia neck (usually < 2 cm), making strangulation very common (24% of patients at presentation)
Treatment
- Surgical treatment recommended in virtually all patients due to high risk of strangulation and incarceration
- Surgical treatment can be performed using either open or laparoscopic technique, although laparoscopic treatment has now become preferred option
- Surgical treatment usually performed with primary mesh repair or mesh reinforcement
- Recurrence rates after mesh repair are quite low

DIAGNOSTIC CHECKLIST

Consider
- Pre-/intraoperative US for accurate localization of SH, especially in obese patients - Extensive intraoperative dissection, distortion of tissue planes, and morbidity risks may be avoided
Image Interpretation Pearls
- Incisional hernias lateral to rectus muscle can mimic SH - Incisional hernias have no intact external oblique muscle or aponeurosis

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References

Selected References

Differential diagnosis

Abdominal Wall Mass

DDX:d51e2268-67b6-4a60-9222-f5a86f61ddec

Acute Left Abdominal Pain

DDX:65c32297-ce9e-41dd-80b5-60fd7160f2a6

Defect in Abdominal Wall (Hernia)

DDX:5af046fa-59ef-45b5-952b-acbcdee36196

Cases

{'cases': [{'authors': [{'key': '64470aa4-5429-4786-81fa-be44c86ca020', 'value': 'Kristine S Spinelli, MD'}], 'caseVersionId': 'c5463905-e3f8-4cd0-a8de-0aa0b61e8e55', 'description': 'Classic spigelian hernia on CECT.\n\nA loop of large intestine is seen herniated lateral to the rectus abdominus muscle (arrow, #1-3), consistent with a spigelian hernia.', 'history': None, 'imagePoolId': 'af273cd7-9a32-4a1b-b833-5dac98949716', 'name': 'Classic', 'teachingPoint': None, 'demographics': '65 Years old male'}, {'authors': [{'key': '3d84d682-9451-4b02-99b2-e34970a5b440', 'value': 'Michael P. Federle, MD, FACR'}], 'caseVersionId': 'cc436c73-ea4f-45ce-bd88-4db6ade70016', 'description': 'Axial CECT shows aortic and iliac aneurysms and an incidental spigelian hernia. The hernia (open arrow, #1) contains a segment of ascending colon, but there is no sign of bowel obstruction.', 'history': 'Elderly man being evaluated for an abdominal aortic aneurysm.', 'imagePoolId': '9571e5a8-af45-4e4b-8cd5-6a171815798c', 'name': 'Incidental finding', 'teachingPoint': None, 'demographics': '76 Years old male'}, {'authors': [{'key': '3d84d682-9451-4b02-99b2-e34970a5b440', 'value': 'Michael P. Federle, MD, FACR'}], 'caseVersionId': 'e7340c27-1d19-43a2-917f-e918df5add1c', 'description': 'CT shows a small bowel obstruction and a spigelian hernia.\n\nThe hernia (open arrow, #2) is evident, just lateral to the rectus muscle. A segment of small bowel herniates through the defect, resulting in partial obstruction. The hernia and obstruction were confirmed and corrected at surgery.', 'history': 'Middle-aged woman with distended abdomen and abdominal pain.', 'imagePoolId': 'e81acda9-0fe8-4001-8c86-e483141eeebd', 'name': 'With partial bowel obstruction', 'teachingPoint': None, 'demographics': '62 Years old female'}, {'authors': [{'key': '3d84d682-9451-4b02-99b2-e34970a5b440', 'value': 'Michael P. Federle, MD, FACR'}], 'caseVersionId': 'ea9291ee-372a-4332-b115-a57f974b92d1', 'description': 'CT shows herniation of descending colon through spigelian aponeurosis.\n\nA frontal radiograph (#1) shows the distorted and displaced descending colon (arrow). Note the defect (open arrow, #4) in the abdominal wall lateral to the rectus muscle, through which a portion of the descending colon herniates. Note that the external oblique muscle (curved arrow, #2) and its aponeurosis remain intact, making the hernia sac an intramuscular process, which is classic for a spigelian hernia.', 'history': None, 'imagePoolId': '54664b68-275e-40eb-90aa-a8a8a0fe1aff', 'name': 'Classic, with colon', 'teachingPoint': None, 'demographics': '52 Years old male'}], 'caseType': 'typical', 'name': 'TYPICAL'}
{'cases': [{'authors': [{'key': '3d84d682-9451-4b02-99b2-e34970a5b440', 'value': 'Michael P. Federle, MD, FACR'}], 'caseVersionId': '8fe62ec3-1a09-40ef-b14a-99463fe13e8c', 'description': 'CT shows distended, ischemic bowel, obstructed in a spigelian hernia.\n\nFree air (curved arrow, #1) indicated bowel perforation. The small intestine is dilated and pneumatosis (arrow, #2-4) indicates bowel ischemia. The point of obstruction was a spigelian hernia (open arrow, #4).\n\nComment: Infarcted bowel was resected at surgery, but the patient expired soon after surgery.', 'history': 'Elderly woman with distended abdomen and pain.', 'imagePoolId': '5290ab4d-9f98-4d51-b5b2-1ce3ef0f25ac', 'name': 'With bowel obstruction and ischemia', 'teachingPoint': None, 'demographics': '92 Years old female'}, {'authors': [{'key': '3d84d682-9451-4b02-99b2-e34970a5b440', 'value': 'Michael P. Federle, MD, FACR'}], 'caseVersionId': 'c4d2db95-3bb0-4f9c-9388-b9d0a3ee2490', 'description': 'Axial CECT shows a spigelian hernia, with herniation of omental fat through a defect in the aponeurosis of the transverse abdominal and internal oblique muscles, covered by an intact aponeurosis of the external oblique muscle. Also present within the hernia is a thick-walled tubular structure (arrows, #1-4) (inflamed appendix), seen arising from the tip of the cecum.', 'history': 'Right lower quadrant pain & fever.', 'imagePoolId': '9333dddf-fbad-4976-ba1b-8d74d01ca29b', 'name': 'Inflamed appendix within spigelian hernia', 'teachingPoint': None, 'demographics': '81 Years old male'}, {'authors': [{'key': '3d84d682-9451-4b02-99b2-e34970a5b440', 'value': 'Michael P. Federle, MD, FACR'}], 'caseVersionId': '0a940857-19ac-4e61-89d0-ca2c275d88ab', 'description': 'A series of axial (#1-7) and coronal reformatted (#8-14) CT sections shows an intact external oblique muscle and its aponeurosis (curved arrows, #2-5,10-13), though these are thin and stretched over a subtle fat density bulge in the left lower abdominal wall, caudal and lateral to the umbilicus (open arrows, #1,8). A defect in the aponeurosis of the internal oblique and transverse abdominal muscles (arrows, #6,12-13) is a Spigelian hernia, and the herniated omental fat accounts for the other signs and symptoms.\n\nComment: The intact external oblique muscle is a distinguishing feature not found in cases of incisional hernias, which may occur in the same location.', 'history': 'Pain sharply localized to the left lower quadrant on straining.', 'imagePoolId': '24dd810d-998e-4ae6-8a53-edbd3aaaa6a1', 'name': 'Small and subtle', 'teachingPoint': None, 'demographics': '37 Years old male'}], 'caseType': 'variant', 'name': 'VARIANT'}

Images

Selected Images

Axial CECT demonstrates a Spigelian hernia arising just lateral to the rectus muscle. A segment of small bowel herniates through the defect, resulting in partial obstruction. The hernia and obstruction were confirmed and corrected at surgery.

Axial NECT demonstrates a small Spigelian hernia in the left lower quadrant, inferior and lateral to the umbilicus. Note the layer of the external oblique muscle overlying the hernia sac.

Axial NECT in a patient being imaged for iliac aneurysms demonstrates an incidental spigelian hernia. The hernia contains a segment of ascending colon, but there is no sign of bowel obstruction.

Axial CECT shows a small bowel obstruction and a Spigelian hernia . A segment of small bowel herniates through the defect, resulting in obstruction and dilatation of the upstream bowel .

Additional Images

Axial CECT shows a Spigelian hernia just lateral to the rectus muscle with an obstructed, herniated descending colon.

Axial CECT shows a left Spigelian hernia .

Axial NECT shows a loop of large intestine herniating lateral to the rectus abdominis muscle, consistent with a Spigelian hernia.

Axial NECT shows aortic and iliac aneurysms and an incidental Spigelian hernia . The hernia contains a segment of ascending colon, but there is no sign of bowel obstruction.

Axial CECT shows a Spigelian hernia with herniation of omental fat through a defect in the aponeurosis of the transverse abdominal and internal oblique muscles, covered by an intact aponeurosis of the external oblique muscle. Also present within the hernia is a thick-walled tubular structure (inflamed appendix) seen arising from the tip of the cecum.

Axial T2 MR demonstrates a Spigelian hernia in the left lower quadrant, inferior and lateral to the umbilicus. Note the layer of the external oblique muscle overlying the hernia sac.

Axial CECT in a patient with left lower quadrant pain demonstrates a Spigelian hernia containing a fat-containing lesion , which extends from the surface of the colon with adjacent fat stranding or inflammation. This represents epiploic appendagitis within a Spigelian hernia.

Axial CECT demonstrates a Spigelian hernia containing a fat-containing lesion , which extends from the surface of the colon with adjacent fat stranding or inflammation. This represents epiploic appendagitis within a Spigelian hernia.

26 KiB Raw Permalink Blame History

KEY FACTS

Terminology

Imaging

Top Differential Diagnoses

Pathology

Clinical Issues

TERMINOLOGY

Abbreviations

Synonyms

Definitions

IMAGING

General Features

Best diagnostic clue

Location

Morphology

CT Findings

Imaging Recommendations

Best imaging tool

Ultrasonographic Findings

DIFFERENTIAL DIAGNOSIS

Subcutaneous or Intramuscular Lipoma

PATHOLOGY

General Features

Etiology

Associated abnormalities

Gross Pathologic & Surgical Features

CLINICAL ISSUES

Presentation

Demographics

Age

Sex

Epidemiology

Natural History & Prognosis

Treatment

DIAGNOSTIC CHECKLIST

Consider

Image Interpretation Pearls

References

Selected References

Differential diagnosis

Abdominal Wall Mass

Acute Left Abdominal Pain

Defect in Abdominal Wall (Hernia)

Cases

Images

Selected Images

Additional Images

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Raw Permalink Blame History