This is an article from 1953 about the epi-sacro-iliac lipoma and sciatica (these lipomas are also known as back mice). Sheehan starts presenting 6 illustrative cases with these lipomatous masses and low back pain and sciatica.

Case 1. A 63-year-old man
Case 2. A 23-year-old woman
Case 3. A 38-year-old man
Case 4. A 35-year-old man
Case 5. A 45-year-old man
Case 6. A 48-year-old man

Sheehan was a known surgeon that worked at Our Lady of Lourdes Hospital in Drogheda, Ireland. He uses a very detailed anatomical description of the “basic fat pads”. Unfortunately, he does not support any original drawings or photos, just the “already published drawings” that were originally from Copeman and Ackerman. The lack of images is a problem for many articles from that period, so it makes it difficult to reflect the findings in the anatomical books and to spread the knowledge of these fatty structures.

Epi-sacro-iliac lipoma and sciatica

By Vincent Sheehan, M.Ch., F.R.C.S.

Our Lady of Lourdes Hospital, Drogheda, Ireland

Published in 1953 in the Journal of the Irish Medical Association.

Sheehan presents 6 case histories

Case 1. A 63-year-old man. Presented severe pain over his left sacro-iliac joint for 10 days. No history of trauma. Pain locally on pressure along upper margin of the left sacro-iliac joint, and along the sciatic nerve to level of the mid-calf. Local injection into the nodule of procaine 2% gave immediate relief, but only for one day. Sheehan decided then to remove the nodule surgically under general anesthesia. They removed a 1-1/2 inch-long spindle-shaped fatty swelling, which had herniated through a defect in the DEEP FASCIA at the upper margin of the left sacro-iliac joint. The patient experienced permanent relief since then (1951).
Case 2. A 23-year-old woman. The patient presented 12 months of bilateral sciatica and lumbo-sacral pain. Palpation showed 2 fatty nodules over each sacro-iliac joint at its upper margin. Both masses were removed with good outcome (one was quarter-inch in diameter and the other half an inch long).
Case 3. A 38-year-old man. Patient with 14 months history of left sciatica and lumbo-sacral backache and 2 weeks history of right sciatica. On operation the trigger points were found to be lipomatous swellings (half inch and one-eighth of an inch in diameter). Removal was curative. No recurrence.
Case 4. A 35-year-old man. He presented moderate right-sided sciatica of 2 years duration. And disabling left sciatica of nine months. On removal 2 nodules were found, one in each side (inch and a half and half an inch diameter). Excision was curative, no recurrence.
Case 5. A 45-year-old man. He presented severe right-sided sciatica, which confined him to bed for 2 and a half months. He said that he had wrenched his back lifting the wheel of a truck. Since then, he felt a tender nodule. Procaine 2% test gave relief of the sciatica for 3 days, but the sacro-iliac pain for 6 hours. They performed an excision of a 3/4-inch diameter. There was complete relief and no recurrences.
Case 6. A 48-year-old man. He presented a 6-year history of intermittent attacks of intractable right sciatica and sacroiliac pain. Procaine 2% test gave temporary relief. A 2 1/2 inches of lipomatous mass was removed by surgery. He obtained immediate relief.

Nature of the pain

What do they know about “fibrositis”?

Sheehan states that fibrositis of the back (personal note: another name that received the back mice) is a RECOGNIZED CLINICAL ENTITY although its etiology has been a matter of speculation.

Comroe (1942) in his late work stated that etiology of fibrositis was unknown and that there were not any pathological lesions.

Fibrositis clinically presents as tender nodules or/and localized trigger points in certain typical localizations.

Sheehan definition of the trigger points

The tender points where the referred pain can originate have many names: trigger-points, tender rheumatic nodules, and myalgic spots. These points are clinical entities, when they are found by the palpating finger and pressed, the patient winces involuntarily because of pain. Pressure of the same intensity a few millimeters away will not produce the same response. The patient may also present a certain degree of muscular tenderness. The pressure on the tender point can refer pain to other areas. If a local anesthetic is injected in the center of the tender point, it gives immediate relief.

Sheehan explains Copeman’s study about the typical “pain pattern” of fibrositis

Copeman studied 50 cases of patients with fibrositis.

The dorsal region

The most CONSTANT point of tenderness is over the supraespinatus tendon, just before it passes deep to the acromion.
In the inter-scapular region tender spots may occur anywhere in the vertical plane within 2 1/2 inches of the midline, which presents the width of the sacrospinalis muscle at this level.
Tender spots along the medial border of the scapula from the level of its spine downwards.

The lumbar region

Tender spots along the edge of the sacrospinalis muscle just above the iliac crest.
Tender spots around one inch below the iliac crest.
Tender spots at the level at which the latissimus dorsi crosses the sacrospinalis.

The gluteal region

Tender points may be found along the crest of the ilium and for a distance about 2 inches below it.
Tender spots along the sacro-iliac junction where the deep fascia is attached.

Sheehan comments on Copeman’s theory about etiopathogeny of the trigger points and nodules

He mentions Copeman’s theories, which stated that the causative agent of pain would be the RECURRENT EDEMA painfully distending certain fat lobules in the deep subcutaneous tissue (he also mentions that no evidence of focal infection has been established).

Sheehan explains Copeman’s observation about the new presentation of the nodules

Copeman observed that certain pain in the back which accompanied most pyrexal illnesses (influenza, fevers, malaria, dysentery and infective hepatitis) is of the same characteristics and pattern as fibrositis. Copeman concluded that the nodules form then and, in certain patients, they disappear whereas in certain patients they persist unknown by the person. Later in life, certain infections or injuries may reactivate the condition. These nodules tend to occur in certain predictable cervico/dorsal and lumbo/gluteal areas.

Sheehan explains about Copeman’s “basic fat pattern” and its correlation with the “pain pattern”

In 1944 Copeman reported 10 cases where the surgical removal of the fatty tumor gave a striking relief.

Copeman and Ackerman got intrigued by the clinical entity of fibrositis after being aware of the high prevalence of this clinical entity among young healthy soldiers.

First of all, they plot the exact site of nodules and trigger painful spots in a large number of patients. They presented a “pain pattern chart”.

Later, by cadaveric dissection, they could correlate the painful spots of the pain chart with the FAT DEPOSITS of residual fat that they found even in cadavers with the grossest forms of cachexia. That’s why they named these deposits as BASIC FAT PADS.

Notes about the FASCIAS

Beneath the subcutaneous fat an areolar tissue of the back lies in highly vascular superficial fascia, which forms a continuous sheet from the neck to the gluteal region.

The space between the superficial and deep fascia is mainly potential, containing little or NO fat. In certain well-defined places, however, deposits of pinkish fat constantly occur. These, with equally constant deep areas, constitute the basic fat pattern. These are present in even most wasted bodies in which most of the fat elsewhere has disappeared.

IN OBESE PERSONS, this fat pattern tends to be obscured by more generalized deposition of fat.

The fascias of the back are not of uniform thickness, being notably thinner in certain places and, frequently, there are actual deficiencies in the fascial membranes. In these places the underlying fat tends to bulge through sometimes, resulting in a complete herniation, fat hernia.

These fat pads are better described in regions:

Dorsal region:

The basic fat pad is lying along the tendon of the supra-spinatus muscle running out towards the shoulder, where it becomes incorporated in the synovial sheath of the tendon.
It outlines the borders of the investing fascia of the trapezius.
Also at the medial border of the scapula from its spine downwards.
At the junction of the lower costal margin and the outer border of the sacrospinalis muscle. (The cases where synovial fat was seen lying beneath, it seemed to be under much tension, bulging out when this muscle was divided).

Lumbar region:

The sacrospinalis muscle is edged with fat, some lying superficial to the deep fascia (lumbar fat pad) and some lying within the angle made by the deep fascia as it splits to invest this muscle.
In very wasted bodies, fat is deficient along the upper part where it lies under cover of the latissimus dorsi, but below this strip the fat follows the line of attachment of the deep fascia and the muscle along the sacro-iliac junction.
Small fatty herniae have frequently been observed in both these areas.
It is not uncommon to find at intervals, along the edge of the sacroespinalis muscle, a small BUBBLE OF DEEP FASCIA containing a few LOBULES OF FAT bulging up from the angle in which it is contained, and firm pressure can easily convert it into a true fat hernia. These small herniae tend to occur at points where the fascia is weak and do not give rise to symptoms until some incident such as sudden trauma or some pyrexial illness, which entails lying on the back for several days, produces an increase in the fat pressure and painful degree of distension. This leads to edema, which perpetuates the condition.

Gluteal region:

There is a crescent of pink fat extending along the crest of the ilium and for about two inches below it. It is contended within the superficial fascia and extends from the anterior superior spine back to the sacro-iliac junction, often sending a narrow prolongation down this area.
A similar tongue of fat lies in this region, but at a deeper level, being contained in the angle of the deep fascia. It is thus continuous with the fat along the edge of the sacrospinalis muscle in the lumbar region.
The fat along the iliac crest lies in layers, where it has split the superficial fascia in which it is contained and it is common for lobules of one layer to herniate into a more superficial layer or laterally into an adjoining compartment where the fibrous walls are weak and deficient.
The fact that this pad of fat lies almost directly over the unyielding iliac bone may account for the common occurrence of such lesions in this area.

Copeman’s types of fat herniation

Context. The anatomical studies of Copeman and Ackerman showed that fibrositic pain or trigger points of pain in the back have a topographic relationship to the basic fat pattern.

Herniation of fat lobules through fascial weaknesses, deficiencies or foramina was found in dissections and such herniation was proved to be sites of pain in living patients.

When tender points were explored, herniation of DISTENDING FAT LOBULES through deficiencies in their investing fibrous covering was frequently found.

Removal or disruption of these herniae resulted in lasting relief.

Fat which lies under a fascial covering, as in the angle of the deep fascia where it splits to invest the sacrospinalis muscle or along the crest of the ilium, is always under tension and so it will bulge into any potential space resulting from congenital weakness or trauma. This tendency will be increased by muscular activity.

Copeman and Ackerman differentiated three types of fat herniae:

Non-pedunculated type:

It occurs from the deeper layer of fat through a fascial covering or layer into a more superficial layer. It is most commonly found in the lumbar fat pad, lying within the superficial fascia and in its extension downward along the crest of the ilium and in the gluteal region.

These tense swollen fat nodules are palpable when sufficiently superficial. When a nodule disappears as a result of heat or massage, it seems reasonable to suppose that it has been composed of fat rather than a fibrous tissue (personal note: in my opinion it may not disappear; it may just get not palpable and, therefore, less symptomatic).

A variant of this type is that which protrudes in a horizontal direction, the contents of one of the fibrous compartment herniating through an imperfection in the wall of the neighboring compartment as a result of some extra tension – THIS TYPE OCCURRED MOST FREQUENTLY along the iliac crest.

Pedunculated type:

This type of hernia occurs from the deeper layer of fat through a fascial covering or layer into a more superficial layer.

Copeman and Ackerman found no pedunculated hernia in normal backs dissected post-mortem, but several were found and removed in patients subjected to operation. THE POLYPOID FATTY MASS lies in a layer of fat more superficial than that from which it springs. In each of these cases there had been sudden onset of pain produced by a strain several years previously.

(Personal note: There are later studies by surgeons who excised bilateral polilobulated fatty masses in that lumbar region, which were reported to have a peduncle or stalk that connects them to deeper tissues. This bilaterality would be difficult to explain by a traumatic agent; personally I would suggest that it could have a more congenital origin).

Foraminal type:

The fat hernia occurs along the foramina which exists in the deep fascia of the sacrospinalis muscle along which the lateral branches of the posterior primary divisions of the 1st, 2nd and 3rd lumbar nerves (or superior cluneal nerves) with small artery and vein pass.

Copeman and Ackerman reported that the foramina hernia occurred only along the edges of the sacrospinalis muscles. These muscles are supplied by the lumbar nerves, where the lateral branches BECOME CUTANEOUS and pierce the deep fascia at the spot where the trigger points of pain chiefly occur.

In several cases, a small tuft of fat lobules had herniated through the foramen and was found to be the cause of sudden lumbago and removal of the edematous fat and enlargement of the foramen proved curative.

Though herniation might theoretically occur in any of the nerve foramina, it has been proved to do so only in the cases of the 2nd and 3rd lumbar nerves, whose foramina are not overlapped by the latissimus muscle.

These two nerve foramina were NOT OVERLAPPED in any of the fourteen bodies dissected by Copeman, though reference to Gray’s anatomy would suggest that they generally overlapped.

HERZ’S RESULTS

Of the six cases in Herz’s first report in 1945:

5 were non-pedunculated
1 had discernible pedicle

SHEEHAN’S REPORT

Of the six cases in Sheehan’s report:

5 were non-pedunculated
1 was pedunculated

Pathological findings of the fat herniae:

They found in practically every case nothing but normal fat tissue distended with oedematous fluid.
In Sheehan’s series, Dr. Frank Geoghegan reported “fatty tissue of lipomatous nature”.
Nervous tissue was found in NO case.

Clinical considerations:

-In all of Herz’s cases there was a history of trauma initiating the pain.

-In one of Sheehan’s cases there was definite history of injury.

Sheehan’s main characteristics:

-In all cases pain in the back was severe, mainly localized in the epi-sacro-iliac region on one or both sides.

-There was the presence of a palpable tender mass, which acted as a trigger point for the pain.

-In some instances the pain was referred down the leg along the sciatic distribution.

-Injection of the fatty masses with local anesthetic (procaine or metycaine or xylocaine) provided temporary relief in all instances.

-In some cases, the condition was bilateral, though symptoms were more severe on one side.

TREATMENT

Injection has a limited scope: If very accurate injection of the lobule is done and a large amount of local anesthetic solution injected under high pressure, it is possible to disrupt the lobule by hydrostatic pressure.

UNDERCUTTING or “teasing”. Copeman’s technique while performing the injection used the needle to disrupt the pedicle or the capsule of the fat lobules, with the aim of breaking the pathological structure.

SURGERY: Excision is very satisfactory. No recurrences reported in Sheehan’s cases.

Overall results

–Herz has the largest series. 68 operated cases with 62 free of pain.

–Hucherson has 42 cases all with permanent relief.

-Copeman reported 22 cases all with permanent relief.

-Sheehan reported 6 cases all with permanent relief.

Published in September 2018 by Marta Cañis Parera

References

SHEEHAN V. Epi-sacro-iliac lipoma and sciatica. J Ir Med Assoc. 1953 Jun;32(192):173-7. PubMed PMID: 13052999.
Copeman 1949
Herz 1945