TANAKA INDEX CT SCAN OF INCISIONAL HENIA

TANAKA INDEX CT SCAN OF INCISIONAL HENIA\

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Tanaka index incisional hernia CT scan

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Tanaka index CT scan incisional hernia loss of domain volumetry

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https://www.frontierspartnerships.org/journals/journal-of-ab…

Here is a detailed overview of the Tanaka Index in the context of CT scan assessment of incisional hernias:

Tanaka Index - CT Scan Assessment of Incisional Hernia

Background

The Tanaka Index was introduced by Tanaka EY et al. (2010) in the journal Hernia as a CT-based volumetric method to quantify Loss of Domain (LOD) in complex large incisional hernias. The original paper is: "A computerized tomography scan method for calculating the hernia sac and abdominal cavity volume in complex large incisional hernia with loss of domain." Hernia 14:63-69.

What is Loss of Domain (LOD)?

Loss of domain refers to the condition where a significant portion of the abdominal viscera has herniated out of the abdominal cavity and can no longer be safely returned without risking abdominal compartment syndrome (ACS). The larger the hernia relative to the total abdominal volume, the greater the LOD.

The Tanaka Index Formula

Tanaka Index (TI) = HSV / ACV

Term	Definition
HSV	Hernia Sac Volume
ACV	Abdominal Cavity Volume

Both volumes are measured from CT scan using the ellipsoid volume formula:

V = (π/6) × L × W × H

Where L, W, and H are the three orthogonal diameters (longitudinal, transverse, anteroposterior) of the structure, measured in centimeters on CT.

Abdominal Cavity: measured from the diaphragm superiorly to the pelvic floor inferiorly, bounded laterally by the abdominal wall
Hernia Sac: measured from the neck of the defect to the outermost extent of the sac

Threshold and Clinical Significance

Tanaka Index Value	Interpretation
< 0.25	No significant loss of domain; standard repair feasible
> 0.25	Loss of domain hernia; complex repair required
0.25 - 0.30	Mild LOD - TAR (Transversus Abdominis Release) alone
0.31 - 0.35	Moderate LOD - TAR + peritoneal flap reinforcement
> 0.35	Severe LOD - preoperative preparation required (Botulinum toxin + Progressive Pneumoperitoneum), then TAR + peritoneal flap

Surgical Decision-Making Algorithm (Tanaka Index-based)

CT Abdomen
     |
  Calculate TI = HSV / ACV
     |
  TI < 0.25 ─────────────────────────────────┐
     |                                         |
  TI > 0.25 (Loss of Domain)           Defect size guides:
     |                                    <12cm: Onlay mesh
     ├── 0.25-0.30: TAR alone             >12cm: TAR + retrorectus mesh
     |
     ├── 0.31-0.35: TAR + peritoneal flap
     |
     └── >0.35: BT injections + PPP (Days 1-24)
                  → Surgery Day 24-30
                  → TAR + peritoneal flap

Why CT Scan?

CT (preferably with Valsalva maneuver) provides:

Volumetric measurements of the hernia sac and abdominal cavity
Defect width and location (EHS classification)
Hernia contents (bowel, omentum, solid organs)
Prior mesh position, integrity, migration, or infection
Associated hernias (inguinal, parastomal)
Condition of abdominal wall muscles (atrophy, diastasis recti)

In a 2026 multi-criteria survey of 61 abdominal wall reconstruction specialists, the Tanaka Index was ranked 6th most important CT parameter out of 16, with a mean clinical relevance score of 8.45/10 - Hernia journal survey.

Comparison: Tanaka vs. Sabbagh Method

Feature	Tanaka Method	Sabbagh Method
Formula	HSV / ACV	HSV / (ACV + HSV)
LOD threshold	> 0.25	> 20%
Volume method	Ellipsoid formula	Semi-automated volumetry
Posterior ACV boundary	Anterior aspect of vertebral body	Anterior aspect of vertebral body
Complexity	Simple, manual	More precise, semi-automated

Both methods yield closely correlated hernia sac volumes (r = 0.91).

Clinical Implications

A TI > 0.25 signals that forceful visceral reduction will raise intra-abdominal pressure (IAP) dangerously
Preoperative Botulinum toxin (BT) injections into the lateral abdominal wall muscles cause temporary paralysis and lateral abdominal wall elongation, increasing functional abdominal volume
Progressive Pneumoperitoneum (PPP) gradually re-expands the abdominal cavity to accommodate the herniated contents
These measures, guided by the Tanaka Index severity, reduce the risk of ACS postoperatively and enable safe fascial closure

Key Reference

Tanaka EY, Yoo JH, Rodrigues AJ Jr, Utiyama EM, Birolini D, Rasslan S (2010). A computerized tomography scan method for calculating the hernia sac and abdominal cavity volume in complex large incisional hernia with loss of domain. Hernia, 14:63-69.

PRIVED IMAGES GOW TO MEASURES HSV AND ACV

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CT scan hernia sac volume abdominal cavity volume measurement Tanaka index

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Tanaka index CT scan how to measure HSV ACV hernia sac abdominal cavity volume images diagrams

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Excellent - got two real CT scan examples directly from an ECR 2025 radiology poster. Also pulling a YouTube video that visually demonstrates the measurement technique.

How to Measure HSV and ACV on CT Scan - Tanaka Index

The Core Principle

Both the hernia sac and the abdominal cavity are treated as ellipsoids on CT. You measure 3 diameters of each and plug them into:

Volume = 0.52 × a × b × c

Where a = cranio-caudal (CC), b = transverse (latero-lateral), c = anteroposterior (AP)

CASE 1 - Moderate Loss of Domain

What the arrows show:

Pink arrows (ACV measurements): Axial slice shows ACV transverse = 17.9 cm (top left); ACV AP = measured in sagittal; ACV cranio-caudal = 34.2 cm (sagittal, right panel)
Green arrows (HSV measurements): Hernia sac CC = 15.1 cm, AP = 6.5 cm (sagittal, middle); HSV transverse = 20.5 cm (axial, bottom middle)
Yellow dashed lines = cranial and caudal limits of the abdominal cavity

Result:

HSV = 1046 mL
ACV = 9454.4 mL
LOD = 1046 / 9454.4 = 0.11 (<25%) - No loss of domain

CASE 2 - Massive Loss of Domain

What the arrows show:

Pink arrows = ACV measurements (axial and sagittal)
Green arrows = HSV measurements (axial for transverse + AP; sagittal for cranio-caudal)
Yellow dashed lines = cranial/caudal limits of ACV on sagittal view

Result:

HSV = 7819 mL
ACV = 7003 mL
LOD = 7819 / 7003 = >25% (>1.0) - Massive loss of domain

Step-by-Step Measurement Protocol

STEP 1 - Identify the Landmarks

Structure	Cranial limit	Caudal limit	Anterior limit	Posterior limit
ACV	First slice showing diaphragm	Last slice showing coccyx	Line joining healthy anterior muscle groups	Line through transverse processes of vertebrae
HSV	Parietal peritoneum of sac (cranial)	Parietal peritoneum of sac (caudal)	Outer skin/sac wall	Same posterior line as ACV

STEP 2 - Measure 3 Diameters on CT

On axial slices - measure the widest transverse (b) and AP (c) diameters of each ellipsoid

On sagittal slices - measure the cranio-caudal (a) height of each ellipsoid

Always take the largest single measurement across all slices - do not average; use the maximum diameter found anywhere in the scan.

STEP 3 - Apply Ellipsoid Formula

HSV (mL) = 0.52 × a(CC) × b(Transverse) × c(AP)
ACV (mL) = 0.52 × A(CC) × B(Transverse) × C(AP)

STEP 4 - Calculate Tanaka Index

Tanaka Index = HSV / ACV

< 0.25  → No LOD → Standard repair
0.25-0.30 → LOD → TAR technique
0.31-0.35 → LOD → TAR + peritoneal flap
> 0.35  → Severe LOD → Botox + PPP preoperatively, then TAR

Video Demonstration

This YouTube video walks through the actual CT measurements for both Tanaka and Sabbagh methods with real cases:

Watch "https://www.youtube.com/watch?v=b2vhoKVhOAQ" on YouTube

https://www.youtube.com/watch?v=b2vhoKVhOAQ

Key Points to Remember

Pink/magenta arrows on CT = ACV measurements; Green arrows = HSV measurements (this is the standard color convention used in teaching material)
The yellow dashed lines mark the cranial and caudal limits of the abdominal cavity on sagittal view
The ACV's posterior boundary passes through the transverse processes of vertebrae - NOT the anterior vertebral body (that is the Sabbagh method's boundary)
The formula constant 0.52 comes from simplifying (4/3 × π × r1 × r2 × r3) when using full diameters instead of radii: 4/3 × π × 1/8 ≈ 0.5236 ≈ 0.52
CT with Valsalva maneuver is preferred as it maximally distends the hernia sac, giving a more accurate HSV

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