1. Introduction

Inconsistencies in the modeling of concepts related to the congenital absence of all or part of a body structure have been reported to SNOMED International.  The issue appears to stem from the origin of these terms from ICD-9 and ICD-10.  In the ICD classifications, the majority of these terms are classified as “Agenesis, aplasia or hypoplasia of X", and includes index terms "Congenital absence of X" - (Absence (of) (organ or part) (complete or partial)"), and “Agenesis of X".  This is probably the reason that many of the current “Congenital absence of X’ terms include a description of “Agenesis of X”, which is more specific than the overall meaning of the term. While most pediatric professionals use the term "Congenital limb deficiencies", in order to differentiate between longitudinal or transverse and complete vs partial absence, ICD-10 continued to use the term Congenital absence to represent all anomalies of development.  ICD-11 appears to have adopted a more specific approach, using the term "reduction deformities" for limb deficiencies, but still retained some of the older synonymy (e.g. Congenital absence of gallbladder is synonymous to LB20.10 Agenesis, aplasia or hypoplasia of gallbladder).  Many of the terms in question have been in SNOMED CT since the first release, so should be interpreted with that origin in mind. Revisions to the original proposal in red.

E.G.

2. Problem statement

Given the purported history of the origin of this issue, what is it that SNOMED CT means when the FSN says "Congenital absence"?

A number of concepts in this domain were remodeled in 2017 as part of the QI project to represent the notion of complete absence (i.e. agenesis), where this additional synonym was present.  This has lead to an inconsistent representation of "Congenital absence" which was based on the presence or absence of a description that did not necessarily represent the original meaning of the concept.  If the synonym was not present on a concept, then the term was modeled simply as "absence".

According to a number of sources, clinical use of "congenital absence" can represent at least three different classes of absence:

1. Total developmental absence of the affected organ/structure
2. Partial absence of the affected organ/structure
3. In utero amputation of all or part of the affected organ/structure. (e.g., 765206003 |Constriction ring syndrome (disorder)|

Clinically, many professional organizations use the term “Congenital absence” to represent the full range of absences of all or part of a specific body structure.  See:  https://www.cdc.gov/ncbddd/birthdefects/surveillancemanual/chapters/chapter-4/chapter4-5.html. 

As noted in the discussion comments, the conventional use of the terms "Aplasia" and "Agenesis" often regard these as synonymous.  However, proper definitions of these terms suggests a distinction that should be made in the terminology when included in the FSN.

• Aplasia -  Defective development resulting in the absence of all or part of an organ or tissue.
• Agenesis - Absence of an organ due to nonappearance of its primordium in the embryo. (implies complete absence)

Initial proposed guidance resulted in a realignment of the morphologies used in modeling these concepts to the following hierarchy:

418560003 |Absence (morphologic abnormality)|

     45486003 |Aplasia (morphologic abnormality)|

          782173000 |Agenesis (morphologic abnormality)|

It was found that by assigning the finding site of all aplasia concepts to "Part of X", incorrect subsumption occurred as Agenesis concepts did not classify correctly under Aplasia concepts of the same body structure, violating the definition of Aplasia as "all or part of".  Thus, the following revision to the original proposed modeling guidance is submitted. 

In order to conform to the intended meaning of the FSNs as described by the original source, the following modeling patterns are proposed for Congenital absence terms:

3. Congenital absence remodel proposal

3.1. FSNs that specify “Congenital absence of X” (231 concepts) will be modeled using:

ASSOCIATED MORPHOLOGY = 418560003 |Absence (morphologic abnormality)|

OCCURRENCE = 255399007 |Congenital (qualifier value)|

FINDING SITE = “Structure of X”

3.2. FSNs that specify “Aplasia” (92 concepts) 

ASSOCIATED MORPHOLOGY = 45486003 |Aplasia (morphologic abnormality)|or 890175002 |Transverse deficiency (morphologic abnormality)|

OCCURRENCE = 255399007 |Congenital (qualifier value)|

FINDING SITE = “Structure of X”

PATHOLOGICAL PROCESS = "Pathological development process"

3.3. FSNs that specify "Partial absence of X" (5 concepts) will be modeled using: 

ASSOCIATED MORPHOLOGY = 45486003 |Aplasia (morphologic abnormality)|or 890175002 |Transverse deficiency (morphologic abnormality)|

OCCURRENCE = 255399007 |Congenital (qualifier value)|

FINDING SITE = “Part of X”

PATHOLOGICAL PROCESS = "Pathological development process"

3.4. FSNs that specify “Agenesis of X” (85 concepts) or "Complete absence of X" (2 concepts) will be modeled using: 

ASSOCIATED MORPHOLOGY = 782173000 |Agenesis (morphologic abnormality)|

OCCURRENCE = 255399007 |Congenital (qualifier value)|

FINDING SITE = “Entire X” 

PATHOLOGICAL PROCESS = "Pathological development process"

3.5. Additional concepts that use the ASSOCIATED MORPHOLOGY = 24216005 |Congenital absence (morphologic abnormality)| will have the value replaced with 418560003 |Absence (morphologic abnormality)| and an additional OCCURRENCE relationship added, if necessary. 24216005 |Congenital absence (morphologic abnormality)| shall no longer be used to model new content and will be inactivated when all existing occurrences of its use are replaced.

3.6.  Congenital absence of X concepts that contain and additional description of “Agenesis of X” will have the synonym inactivated and pointed to either a new or existing concept representing “Agenesis of X”.

3.7.  Longitudinal limb reduction deformities will be reassigned parent of 22841008 |Phocomelia (disorder)|, where appropriate.

4. Alternative proposal

The inherent ambiguity in the use of the term "Absence" should warrant consideration of replacement with a more specific FSN.  This would allow for a more general representation of limb deficiencies as groupers for the more specific partial or complete absences of structures.  This might be disruptive due to the wide use of the term "Congenital absence" for the full spectrum of body structure deficiencies. Alignment with some of the  more recent limb deficiency classifications may be useful.